Driving circuit and semiconductor device

Abstract

To provide a driving circuit that can prevent the occurrence of undershoot in the driving voltage of a transistor, and a semiconductor device including such a driving circuit.SOLUTION: A driving circuit performs normally-off driving of a transistor circuit in which a normally-on type first transistor and a normally-off type second transistor are connected in series. Power supply voltage wiring is connected between the first transistor and the second transistor. The driving circuit has: a diode arranged between a driving terminal of the first transistor and the second transistor; a third transistor arranged between the power supply voltage wiring and the driving terminal of the first transistor; a fourth transistor arranged between the ground and the driving terminal of the first transistor; a fifth transistor arranged between the driving terminal of the first transistor and the fourth transistor; and a control circuit unit that switches the states of the second, third, fourth, and fifth transistors.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD Embodiments of the present invention relate to a drive circuit and a semiconductor device. [Background technology]

[0002] A known technique involves connecting a normally-off transistor in series with a normally-on transistor to form a transistor circuit and operating the transistor circuit in a normally-off mode. For example, when two such transistor circuits are connected to form a half-bridge circuit and the half-bridge circuit is operated in a switching mode, there is a problem that undershoot occurs in the drive voltage of the transistor included in the high-side transistor circuit when the low-side transistor circuit is turned off. To address this problem, a Zener diode is known to be used to suppress undershoot in the drive voltage. However, the Zener diode has a limited response time, making it difficult to sufficiently suppress undershoot. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-118630 Summary of the Invention [Problem to be solved by the invention]

[0004] The problem to be solved by the present invention is to provide a drive circuit capable of suppressing undershoot from occurring in the drive voltage of a transistor, and a semiconductor device including such a drive circuit. [Means for solving the problem]

[0005] A drive circuit according to an embodiment of the present invention is a drive circuit for normally-off driving a transistor circuit configured by connecting a normally-on first transistor and a normally-off second transistor in series. A power supply voltage wiring, to which a power supply voltage is applied, is connected between the first transistor and the second transistor. The drive circuit according to the embodiment includes: a diode having an anode connected to a drive terminal of the first transistor and a cathode connected to an output terminal of the second transistor; a third transistor disposed between the power supply voltage wiring and the drive terminal of the first transistor; a fourth transistor disposed between the drive terminal of the first transistor and a ground having a reference potential that serves as a reference for the power supply voltage; a fifth transistor disposed between the drive terminal of the first transistor and the fourth transistor; and a control circuit configured to switch each of the second transistor, the third transistor, the fourth transistor, and the fifth transistor between an ON state and an OFF state. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a circuit diagram showing a semiconductor device according to a first embodiment. [Figure 2] FIG. 1 is a circuit diagram showing a semiconductor package according to a first embodiment. [Figure 3] 10 is a diagram showing a current flowing through an external load when a transistor circuit in a high-side semiconductor package is in an OFF state and a transistor circuit in a low-side semiconductor package is in an ON state in the first embodiment. FIG. [Figure 4] 10 is a diagram showing a current flowing through an external load when a transistor circuit in a high-side semiconductor package is in an ON state and a transistor circuit in a low-side semiconductor package is in an OFF state in the first embodiment. FIG. [Figure 5] 4 is a timing chart showing an example of the relationship between the power supply voltage and the gate voltage of each transistor when the transistor circuit of the first embodiment is switched between an ON state and an OFF state. [Figure 6]FIG. 10 is a diagram showing the current flowing in the high-side semiconductor package when a voltage is applied between the drain terminal and the source terminal of the high-side transistor circuit before the power supply of the semiconductor device of the first embodiment is turned on. [Figure 7] 10 is a diagram showing a current that flows when the high-side transistor circuit of the first embodiment is in the OFF state and the low-side transistor circuit is switched from the ON state to the OFF state. FIG. [Figure 8] FIG. 10 is a circuit diagram showing a part of a semiconductor device according to a second embodiment. [Figure 9] FIG. 10 is a circuit diagram showing a part of a semiconductor device according to a third embodiment. [Figure 10] FIG. 2 is a circuit diagram showing a part of a semiconductor device according to a first comparative example. [Figure 11] FIG. 10 is a circuit diagram showing a part of a semiconductor device according to a second comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, a driving circuit and a semiconductor device according to an embodiment will be described with reference to the drawings.

[0008] (First embodiment) FIG. 1 is a circuit diagram showing a semiconductor device 100 according to a first embodiment. The semiconductor device 100 shown in FIG. 1 is a semiconductor device for supplying power to an external load 60. The semiconductor device 100 is used as a power conversion circuit such as a power supply circuit or an inverter circuit by connecting a power source, the external load 60, and a coil 70. The method of connecting the external load 60 and the coil 70 is not limited to the method shown in FIG. 1. The semiconductor device 100 is controlled by a controller 80. Pulse signals PSA and PSB are input to the semiconductor device 100 from the controller 80 via an insulating transmission circuit unit 81.

[0009] As shown in FIG. 1, in the first embodiment, the semiconductor device 100 includes two semiconductor packages 10A and 10B. The semiconductor packages 10A and 10B are connected in series between a power supply VDC that supplies power to an external load 60 and ground GND. The semiconductor package 10A is a high-side semiconductor package connected to the power supply VDC. The semiconductor package 10B is a low-side semiconductor package connected to ground GND. In the first embodiment, the external load 60 is connected in parallel to the semiconductor package 10A with respect to the power supply VDC. A coil 70 is disposed between a wiring portion 71 that connects the semiconductor packages 10A and 10B and the external load 60. The wiring portion 71 connects a transistor circuit 30A to a transistor circuit 30B, which will be described later.

[0010] In the circuits disclosed herein, "another element is disposed between a certain element and another element" means that the other element is disposed on the circuit between the certain element and the other element, tracing from one to the other.

[0011] In the first embodiment, the semiconductor package 10A and the semiconductor package 10B have the same structure, although they differ in the timing of operation of the semiconductor device 100. Therefore, in the following description, the configuration of the high-side semiconductor package 10A will be described as a representative, and a description of the configuration of the low-side semiconductor package 10B may be omitted.

[0012] The semiconductor package 10A includes a transistor circuit 30A and a drive circuit 40A. The semiconductor package 10B includes a transistor circuit 30B and a drive circuit 40B. The semiconductor packages 10A and 10B are configured by encapsulating drive circuits 40A and 40B and transistor circuits 30A and 30B, respectively, in a single package. The drive circuit 40A and the transistor circuit 30A do not necessarily have to be encapsulated in a single package, and the drive circuit 40B and the transistor circuit 30B do not necessarily have to be encapsulated in a single package. The two transistor circuits 30A and 30B are connected in series. The two transistor circuits 30A and 30B form a half-bridge circuit 30H. The transistor circuit 30A and the transistor circuit 30B are connected to each other by a wiring portion 71.

[0013] FIG. 2 is a circuit diagram illustrating a semiconductor package 10A. As shown in FIG. 2, the transistor circuit 30A is configured by connecting a first transistor 31A and a second transistor 32A in series. The first transistor 31A is a normally-on transistor. The first transistor 31A is a field effect transistor (FET). The first transistor 31A is, for example, a high electron mobility transistor (HEMT) using gallium nitride (GaN). The first transistor 31A is a high-voltage element having a withstand voltage of, for example, about 600 V or more. A drain terminal 31d of the first transistor 31A is connected to a power supply VDC. A source terminal 31s of the first transistor 31A is connected to a source terminal 32s of the second transistor 32A. The first transistor 31A is in an ON state when the potential difference between the gate terminal 31g and the source terminal 31s is 0 V. The threshold voltage of the first transistor 31A is a negative voltage value. In the following description, the threshold voltage of the first transistor 31A is −Vth, and the absolute value of the threshold voltage of the first transistor 31A is Vth. The first transistor 31A is turned off when the gate voltage becomes smaller than −Vth with respect to the source terminal 31s.

[0014] The second transistor 32A is a normally-off transistor. The second transistor 32A is a field-effect transistor. In the first embodiment, the second transistor 32A is a P-channel field-effect transistor. More specifically, the second transistor 32A is a P-channel MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). The withstand voltage of the second transistor 32A is lower than the withstand voltage of the first transistor 31A. The second transistor 32A is a low-voltage MOSFET with a withstand voltage of, for example, about 50 V or less. A source terminal 32s of the second transistor 32A is connected to a source terminal 31s of the first transistor 31A. A drain terminal 32d of the second transistor 32A is connected to a wiring portion 71 that connects the two transistor circuits 30A and 30B.

[0015] The transistor circuit 30A, which is composed of the first transistor 31A and the second transistor 32A, can be regarded as a single normally-off field-effect transistor. When the transistor circuit 30A is regarded as a single field-effect transistor, the gate terminal G of the field-effect transistor is the gate terminal 31g of the first transistor 31A, the drain terminal D of the field-effect transistor is the drain terminal 31d of the first transistor 31A, and the source terminal S of the field-effect transistor is the drain terminal 32d of the second transistor 32A.

[0016] In this disclosure, the gate terminal of a field-effect transistor corresponds to the "drive terminal." The drive terminal of a transistor is a terminal to which a voltage is applied to drive the transistor. Of the drain terminal and source terminal of a field-effect transistor, the terminal from which current flows when the field-effect transistor is turned on corresponds to the "output terminal." In other words, in a P-channel field-effect transistor, the drain terminal corresponds to the "output terminal," and in an N-channel field-effect transistor, the source terminal corresponds to the "output terminal."

[0017] In the first embodiment, the drain terminal D of the transistor circuit 30A corresponds to the "first terminal" provided on the first transistor 31A. The source terminal S of the transistor circuit 30A corresponds to the "second terminal" which is the output terminal of the second transistor 32A. In the first embodiment, the transistor circuit 30A functions as a transistor having a gate terminal G which is the drive terminal of the first transistor 31A, a drain terminal D which is the first terminal provided on the first transistor 31A, and a source terminal S which is the second terminal which is the output terminal of the second transistor 32A.

[0018] The drive circuit 40A is a drive circuit that drives the transistor circuit 30A in a normally-off mode. The drive circuit 40A is a gate drive circuit that applies a voltage to the gate terminal G of the transistor circuit 30A, i.e., the gate terminal 31g of the first transistor 31A. The drive circuit 40A includes a semiconductor chip 20A, a resistive element 43, and a capacitor 44. The semiconductor chip 20A includes a power supply voltage terminal 41A, a ground terminal 42A, connection terminals 21, 22, 23, and 24, a power supply voltage wiring 48, a ground 91, a third transistor 33A, a fourth transistor 34A, a fifth transistor 35A, a diode 45, and a control circuit unit 50A.

[0019] The power supply voltage terminal 41A is exposed to the outside of the semiconductor chip 20A. A power supply that drives the drive circuit 40A is connected to the power supply voltage terminal 41A. A power supply voltage VDDA is applied to the power supply voltage terminal 41A. A power supply voltage wiring 48 is connected to the power supply voltage terminal 41A. The power supply voltage VDDA is applied to the power supply voltage wiring 48. The power supply voltage wiring 48 is connected between the first transistor 31A and the second transistor 32A. The power supply voltage wiring 48 is connected to the source terminal 31s of the first transistor 31A and the source terminal 32s of the second transistor 32A.

[0020] The ground terminal 42A is exposed to the outside of the semiconductor chip 20A. A ground having a reference potential VSSA that serves as a reference for the power supply voltage VDDA is connected to the ground terminal 42A. The reference potential VSSA is a potential that serves as a reference when the drive circuit 40A operates. As a result, the potential of the ground 91 of the drive circuit 40A that is connected to the ground terminal 42A becomes the reference potential VSSA. There are no particular limitations on the reference potential VSSA, as long as it is a potential that serves as a reference for the power supply voltage VDDA.

[0021] The connection terminals 21, 22, 23, and 24 are exposed to the outside of the semiconductor chip 20A. A resistive element 43 is connected to the connection terminal 21. A gate terminal 31g of the first transistor 31A is connected to the connection terminal 22. A gate terminal 32g of the second transistor 32A is connected to the connection terminal 23. A drain terminal 32d of the second transistor 32A is connected to the connection terminal 24.

[0022] The third transistor 33A and the fourth transistor 34A are normally-off field effect transistors. In the first embodiment, the third transistor 33A is a P-channel MOSFET. In the first embodiment, the fourth transistor 34A is an N-channel MOSFET. The third transistor 33A and the fourth transistor 34A are connected in series to each other and disposed between a power supply voltage wiring 48 and ground 91. A source terminal 33s of the third transistor 33A is connected to the power supply voltage wiring 48. A drain terminal 33d of the third transistor 33A is connected to a drain terminal 34d of the fourth transistor 34A. A source terminal 34s of the fourth transistor 34A is connected to ground 91.

[0023] The gate terminal 31g of the first transistor 31A is connected between the third transistor 33A and the fourth transistor 34A via the resistive element 43. As a result, the third transistor 33A is disposed between the power supply voltage wiring 48 and the gate terminal 31g of the first transistor 31A. The fourth transistor 34A is disposed between the ground 91 and the gate terminal 31g of the first transistor 31A. The resistive element 43 is disposed between the gate terminal 31g of the first transistor 31A and the third transistor 33A. One end of the resistive element 43 is connected to the gate terminal 31g of the first transistor 31A. The other end of the resistive element 43 is connected to the drain terminal 33d of the third transistor 33A.

[0024] The fifth transistor 35A is a normally-off field-effect transistor. In the first embodiment, the fifth transistor 35A is an N-channel MOSFET. The fifth transistor 35A is disposed between the gate terminal 31g of the first transistor 31A and the fourth transistor 34A. A source terminal 35s of the fifth transistor 35A is connected to the gate terminal 31g of the first transistor 31A. A drain terminal 35d of the fifth transistor 35A is connected to the drain terminal 34d of the fourth transistor 34A.

[0025] The anode of the diode 45 is connected to the gate terminal 31g of the first transistor 31A and the source terminal 35s of the fifth transistor 35A, and the cathode of the diode 45 is connected to the drain terminal 32d of the second transistor 32A.

[0026] The capacitor 44 is disposed between the power supply voltage wiring 48 and the ground 91. One electrode of the capacitor 44 is connected to the power supply voltage wiring 48. The other electrode of the capacitor 44 is connected to the ground 91.

[0027] The control circuit unit 50A is a circuit unit that switches each of the second transistor 32A, the third transistor 33A, the fourth transistor 34A, and the fifth transistor 35A between an ON state and an OFF state. The control circuit unit 50A is disposed between a power supply voltage wiring 48 and a ground 91. A power supply voltage VDDA is input to the control circuit unit 50A. The reference potential in the control circuit unit 50A is a reference potential VSSA. The control circuit unit 50A has a switching circuit unit 51A and a voltage comparison circuit unit 52A.

[0028] The switching circuit unit 51A is disposed between the power supply voltage wiring 48 and ground 91. A power supply voltage VDDA is input to the switching circuit unit 51A. The reference potential of the switching circuit unit 51A is a reference potential VSSA. A pulse signal PSA is input to the switching circuit unit 51A from the controller 80 via the insulating transmission circuit unit 81. An output from the voltage comparison circuit unit 52A is input to the switching circuit unit 51A. A gate terminal 33g of the third transistor 33A, a gate terminal 34g of the fourth transistor 34A, and a gate terminal 35g of the fifth transistor 35A are connected to the switching circuit unit 51A.

[0029] In the first embodiment, the switching circuit unit 51A switches each of the third transistor 33A, the fourth transistor 34A, and the fifth transistor 35A between an ON state and an OFF state based on the pulse signal PSA and the output from the voltage comparison circuit unit 52A. More specifically, the switching circuit unit 51A applies voltages to the gate terminal 33g of the third transistor 33A, the gate terminal 34g of the fourth transistor 34A, and the gate terminal 35g of the fifth transistor 35A based on the pulse signal PSA and the output from the voltage comparison circuit unit 52A, thereby switching the state of each transistor.

[0030] The voltage comparison circuit unit 52A is disposed between the power supply voltage wiring 48 and ground 91. The power supply voltage VDDA is input to the voltage comparison circuit unit 52A. The reference potential of the voltage comparison circuit unit 52A is the reference potential VSSA. The gate terminal 32g of the second transistor 32A is connected to the voltage comparison circuit unit 52A. The voltage comparison circuit unit 52A is a circuit unit that compares the voltage of the power supply voltage wiring 48, i.e., the power supply voltage VDDA, with a voltage higher than the absolute value Vth of the threshold voltage of the first transistor 31A, and outputs the comparison result. The threshold voltage of the normally-on first transistor 31A is a negative value. The comparison result of the voltage comparison circuit unit 52A is output as a voltage value. The comparison result of the voltage comparison circuit unit 52A is output to the switching circuit unit 51A and the gate terminal 32g of the second transistor 32A.

[0031] As shown in FIG. 1, the transistor circuit 30B in the low-side semiconductor package 10B is configured by connecting a first transistor 31B and a second transistor 32B in series. The first transistor 31B is a transistor similar to the first transistor 31A in the high-side semiconductor package 10A. The second transistor 32B is a transistor similar to the second transistor 32A in the high-side semiconductor package 10A. The drain terminal 31d of the first transistor 31B is connected to the drain terminal 32d of the high-side second transistor 32A. The drain terminal 32d of the second transistor 32B is connected to ground GND. In the first embodiment, the transistor circuit 30B corresponds to a "switching element" connected in series to the transistor circuit 30A.

[0032] Similar to the transistor circuit 30A, the drain terminal 31d of the first transistor 31B in the transistor circuit 30B is the drain terminal of the transistor circuit 30B, which is considered to be one field-effect transistor. The drain terminal 32d of the second transistor 32B in the transistor circuit 30B is the source terminal of the transistor circuit 30B, which is considered to be one field-effect transistor. The source terminal S of the transistor circuit 30A, i.e., the drain terminal 32d of the second transistor 32A, is connected to the drain terminal of the transistor circuit 30B, i.e., the drain terminal 31d of the first transistor 31B. This connects the source terminal S of the transistor circuit 30A to the transistor circuit 30B, which is a switching element.

[0033] The drive circuit 40B is a drive circuit that drives the transistor circuit 30B in a normally-off mode. The drive circuit 40B is a gate drive circuit that applies a voltage to the gate terminal of the transistor circuit 30B, i.e., the gate terminal of the first transistor 31B. The drive circuit 40B includes a semiconductor chip 20B, a resistive element 43, and a capacitor 44. The semiconductor chip 20B includes a power supply voltage terminal 41B, a ground terminal 42B, a third transistor 33B, a fourth transistor 34B, a fifth transistor 35B, and a control circuit unit 50B. The control circuit unit 50B includes a switching circuit unit 51B and a voltage comparison circuit unit 52B. A pulse signal PSB is input to the switching circuit unit 51B from the controller 80 via an insulating transmission circuit unit 81.

[0034] A power supply for driving the drive circuit 40 B is connected to the power supply voltage terminal 41 B. A power supply voltage VDDB is applied to the power supply voltage terminal 41 B and a power supply voltage wiring 48 connected to the power supply voltage terminal 41 B.

[0035] A ground having a reference potential VSSB, which is the reference for the power supply voltage VDDB, is connected to the ground terminal 42B. The reference potential VSSB is a potential that serves as a reference when the drive circuit 40B operates. As a result, the potential of the ground 91 connected to the ground terminal 42B of the drive circuit 40B becomes the reference potential VSSB.

[0036] Next, the operation of the semiconductor device 100 will be described. The semiconductor device 100 is controlled based on pulse signals PSA and PSB input from the controller 80. The semiconductor device 100 is controlled so that the ON / OFF state of the transistor circuit 30A in the high-side semiconductor package 10A and the ON / OFF state of the transistor circuit 30B in the low-side semiconductor package 10B are alternately switched. FIG. 3 is a diagram showing the current Ie1 flowing through the external load 60 when the transistor circuit 30A in the high-side semiconductor package 10A is in the OFF state and the transistor circuit 30B in the low-side semiconductor package 10B is in the ON state. FIG. 4 is a diagram showing the current Ie2 flowing through the external load 60 when the transistor circuit 30A in the high-side semiconductor package 10A is in the ON state and the transistor circuit 30B in the low-side semiconductor package 10B is in the OFF state.

[0037] 3, when the high-side transistor circuit 30A is in the OFF state and the low-side transistor circuit 30B is in the ON state, a current Ie1 flows from the power supply VDC to ground GND. The current Ie1 flows from the power supply VDC through the external load 60, the coil 70, and the transistor circuit 30B in that order, and then to ground GND. In this case, energy is stored in the coil 70.

[0038] 4, when the high-side transistor circuit 30A is in the ON state and the low-side transistor circuit 30B is in the OFF state, a current Ie2 flows circulating through a closed circuit formed by the external load 60, the coil 70, and the transistor circuit 30A. At this time, the current Ie2 flows through the external load 60, the coil 70, and the transistor circuit 30A in this order. At this time, the stored energy is released from the coil 70.

[0039] FIG. 5 is a timing chart showing an example of the relationship between the power supply voltages VDDA and VDDB and the gate voltages of the transistors when the transistor circuits 30A and 30B are switched between the ON state and the OFF state. In the following description, the power supply voltages VDDA and VDDB may be collectively referred to as the power supply voltage VDD. Furthermore, the reference potentials VSSA and VSSB may be collectively referred to as the reference potential VSS. VG1A is the gate voltage of the first transistor 31A. VG2A is the gate voltage of the second transistor 32A. VG3A is the gate voltage of the third transistor 33A. VG4A is the gate voltage of the fourth transistor 34A. VG5A is the gate voltage of the fifth transistor 35A. VG1B is the gate voltage of the first transistor 31B. VG2B is the gate voltage of the second transistor 32B. VG3B is the gate voltage of the third transistor 33B. VG4B is the gate voltage of the fourth transistor 34B. VG5B is the gate voltage of the fifth transistor 35B. The gate voltage is the voltage of the gate terminal when the potential of the source terminal is used as a reference. The gate voltage corresponds to the "drive voltage" for driving a field effect transistor.

[0040] The horizontal axis in FIG. 5 represents time t. FIG. 5 illustrates an example in which the semiconductor device 100 is powered on at time t1. When the semiconductor device 100 is powered off, the potential of the power supply voltage wiring 48 is the same as the reference potential VSS, so the power supply voltage VDD is 0 V. When the semiconductor device 100 is powered off, the potential of the gate terminals 31g of the first transistors 31A and 31B is the reference potential VSS, and the potential of the source terminals 31s of the first transistors 31A and 31B is also the potential of the power supply voltage wiring 48, i.e., the reference potential VSS. Therefore, when the semiconductor device 100 is powered off, the normally-on first transistors 31A and 31B are in the ON state. When the semiconductor device 100 is powered off, the other normally-off transistors are in the OFF state. Note that the circuit may be configured so that the fourth transistors 34A and 34B are in the ON state when the semiconductor device 100 is powered off.

[0041] When the semiconductor device 100 is powered on, the power supply voltage VDD rises from 0V to a constant voltage Vd. As the power supply voltage VDD rises, the potential of the source terminal 31s of the first transistors 31A and 31B connected to the power supply voltage line 48 rises. Therefore, the gate voltages VG1A and VG1B of the first transistors 31A and 31B fall by the amount of the rise in the potential of the source terminal 31s. At time t2, after time t1, the value of the power supply voltage VDD becomes equal to the absolute value Vth of the threshold voltage of the first transistors 31A and 31B. At time t2, the gate voltages VG1A and VG1B become the threshold voltage of the first transistors 31A and 31B, i.e., −Vth. After time t2, when the gate voltages VG1A and VG1B become smaller than −Vth, the first transistors 31A and 31B are turned off. At time t4, which is later than time t2, the power supply voltage VDD becomes the constant voltage Vd, and the gate voltages VG1A and VG1B become negative values ​​whose absolute values ​​are the same as the constant voltage Vd, that is, −Vd.

[0042] The voltage comparison circuit units 52A and 52B apply the same voltage as that applied to the source terminal 32s to the gate terminals 32g of the second transistors 32A and 32B to set the gate voltages VG2A and VG2B to 0 V and keep the second transistors 32A and 32B in the OFF state until the power supply voltage VDD exceeds the absolute value Vth of the threshold voltages of the first transistors 31A and 31B. In the first embodiment, the voltage comparison circuit units 52A and 52B short-circuit the power supply voltage wiring 48 and the gate terminals 32g of the second transistors 32A and 32B to set the gate voltages VG2A and VG2B to 0 V until the power supply voltage VDD exceeds the absolute value Vth of the threshold voltages of the first transistors 31A and 31B.

[0043] When the power supply voltage VDD reaches or exceeds a value Vh, which is higher than the absolute value Vth of the threshold voltage of the first transistors 31A and 31B, the voltage comparator circuits 52A and 52B lower the voltage applied to the gate terminals 32g of the second transistors 32A and 32B, turning on the P-channel second transistors 32A and 32B. In the example of FIG. 5, at time t3 between times t2 and t4, the power supply voltage VDD reaches a value Vh. When the power supply voltage VDD reaches or exceeds Vh, the voltage comparator circuits 52A and 52B connect the gate terminals 32g of the second transistors 32A and 32B to ground 91, for example. This causes the gate voltages VG2A and VG2B of the second transistors 32A and 32B to drop by the absolute value of the power supply voltage VDD. When the power supply voltage VDD reaches a constant voltage Vd, the gate voltages VG2A and VG2B of the second transistors 32A and 32B become −Vd. The threshold voltages of the second transistors 32A and 32B are higher than −Vd. Therefore, in the first embodiment, the P-channel second transistors 32A and 32B are turned on when the gate voltages VG2A and VG2B reach −Vd. The second transistors 32A and 32B are always maintained in the on state when the power supply voltage VDD is at a constant voltage Vd. In this way, the control circuit 50A turns on the second transistor 32A when the voltage of the power supply voltage line 48 is higher than the absolute value Vth of the threshold voltage of the first transistor 31A.

[0044] 5, when the switching circuit units 51A and 51B determine based on the output from the voltage comparison circuit units 52A and 52B that the power supply voltage VDD exceeds the absolute value Vth of the threshold voltage of the first transistors 31A and 31B, they apply a voltage equal to or greater than the threshold voltage of each transistor to the gate terminals 34g of the fourth transistors 34A and 34B and the gate terminals 34g and 35g of the fifth transistors 35A and 35B, respectively, to turn on the fourth transistors 34A and 34B and the fifth transistors 35A and 35B. In the example of FIG. 5, when the power supply voltage VDD reaches a value Vh higher than the absolute value Vth at time t3, the switching circuit units 51A and 51B set the gate voltages VG4A and VG4B of the fourth transistors 34A and 34B to Vb and the gate voltages VG5A and VG5B of the fifth transistors 35A and 35B to Vc, thereby turning on the fourth transistors 34A and 34B and the fifth transistors 35A and 35B. The values ​​Vb and Vc are not particularly limited as long as they are gate voltage values ​​that can turn each transistor ON, and may be the same or different values. The values ​​Vb and Vc may also be the same value as the constant voltage Vd.

[0045] When the power supply voltage VDD reaches the constant voltage Vd at time t4, the semiconductor device 100 enters an operable state. At time t4, when the semiconductor device 100 enters an operable state, the first transistors 31A, 31B and the third transistors 33A, 33B are in an OFF state, and the second transistors 32A, 32B, the fourth transistors 34A, 34B, and the fifth transistors 35A, 35B are in an ON state. At time t4, a voltage equal to the power supply voltage VDD is applied to the gate terminals 33g of the third transistors 33A, 33B from the switching circuit units 51A, 51B. As a result, the gate voltages VG3A, VG3B of the third transistors 33A, 33B are 0V at time t4, and the normally-off third transistors 33A, 33B are in an OFF state. When the third transistors 33A and 33B are turned off, the switching circuit sections 51A and 51B short-circuit the gate terminals 33g and source terminals 33s of the third transistors 33A and 33B via the power supply voltage wiring 48, for example.

[0046] The transistor circuit 30A, which can be considered as a single normally-off transistor, is in the ON state when both the first transistor 31A and the second transistor 32A are in the ON state, and is in the OFF state when at least one of the first transistor 31A and the second transistor 32A is in the OFF state. The same applies to the transistor circuit 30B. Therefore, at time t4 when the semiconductor device 100 is in an operable state, each of the transistor circuits 30A and 30B is in the OFF state. While the semiconductor device 100 is supplied with the constant voltage Vd and in an operable state, the second transistors 32A and 32B are always in the ON state. Therefore, the transistor circuits 30A and 30B can be turned ON and OFF by turning the first transistors 31A and 31B ON and OFF, respectively.

[0047] When the semiconductor device 100 is in an operable state, the semiconductor device 100 starts a switching operation that alternates between the ON and OFF states of the transistor circuits 30A and 30B based on pulse signals PSA and PSB input from the controller 80. In the example of FIG. 5 , at time t5, which is after time t4, a pulse signal PSB is input to the low-side switching circuit unit 51B to turn the low-side transistor circuit 30B ON. Based on the pulse signal PSB, the switching circuit unit 51B turns the third transistor 33B ON and the fourth transistor 34B OFF. Specifically, the switching circuit unit 51B applies a voltage to the gate terminal 33g of the third transistor 33B to turn the third transistor 33B ON, and applies a voltage to the gate terminal 34g of the fourth transistor 34B to turn the fourth transistor 34B OFF. In the example of Figure 5, at time t5, the switching circuit unit 51B sets the value of the gate voltage VG3B of the P-channel third transistor 33B to -Va to turn the third transistor 33B on, and sets the value of the gate voltage VG4B of the N-channel fourth transistor 34B to 0V to turn the fourth transistor 34B off.

[0048] When the third transistor 33B is turned on and the fourth transistor 34B is turned off, the gate terminal 31g of the first transistor 31B is shorted to the power supply voltage line 48 via the third transistor 33B, and the gate voltage VG1B of the first transistor 31B becomes 0 V. This turns the first transistor 31B on. When the first transistor 31B is turned on, the low-side transistor circuit 30B is turned on, and a current Ie1 flows as shown in FIG. 3.

[0049] The switching circuit unit 51B switches the fifth transistor 35B between ON and OFF states in accordance with the switching of the fourth transistor 34B between ON and OFF states. Therefore, when switching the fourth transistor 34B to the OFF state at time t5 based on the pulse signal PSB, the switching circuit unit 51B switches both the fourth transistor 34B and the fifth transistor 35B to the OFF state. Specifically, the switching circuit unit 51B applies a voltage to the gate terminal 35g of the fifth transistor 35B to switch the fifth transistor 35B to the OFF state. In the example of FIG. 5, the switching circuit unit 51B sets the gate voltage VG5B of the N-channel fifth transistor 35B to 0 V at time t5 to switch the fifth transistor 35B to the OFF state.

[0050] When the switching circuit unit 51B turns on the fourth transistor 34B based on the pulse signal PSB, it also turns on the fifth transistor 35B along with the fourth transistor 34B. In this way, each of the control circuits 50A and 50B turns on the fifth transistors 35A and 35B when the voltage of the power supply voltage wiring 48 is higher than the absolute value Vth of the threshold voltages of the first transistors 31A and 31B and when the fourth transistors 34A and 34B are on.

[0051] At time t6, a predetermined time after the low-side transistor circuit 30B is turned on, the controller 80 inputs a pulse signal PSB to the switching circuit unit 51B to instruct the low-side transistor circuit 30B to be turned off. At time t6, the switching circuit unit 51B turns the third transistor 33B off and the fourth transistor 34B and the fifth transistor 35B on based on the pulse signal PSB. This causes the first transistor 31B to be turned off again, and the transistor circuit 30B to be turned off.

[0052] At time t6, the controller 80 turns the transistor circuit 30B to the OFF state, and then, after a predetermined dead time, outputs a pulse signal PSA at time t7 to turn the high-side transistor circuit 30A to the ON state. The pulse signal PSA is input to the high-side switching circuit 51A, which turns the high-side transistor circuit 30A to the ON state in the same manner as the switching circuit 51B described above. This causes the current Ie2 to flow, as shown in FIG. 4. Thereafter, the state of the transistor circuit 30A and the state of the transistor circuit 30B are alternately switched in the same manner.

[0053] When the semiconductor device 100 is powered off, the power supply voltage VDD drops from the constant voltage Vd to 0 V. The example in FIG. 5 shows a case where the semiconductor device 100 is powered off at time t8. When the semiconductor device 100 is powered off, the power supply voltage VDD drops, and the gate voltages VG1A and VG1B of the first transistors 31A and 31B rise by the amount of the drop in the power supply voltage VDD. At time t9, which is after time t8, the value of the power supply voltage VDD reaches a value Vh that is higher than the absolute value Vth of the threshold voltages of the first transistors 31A and 31B. The voltage comparator circuits 52A and 52B apply a voltage to the gate terminals 32g of the second transistors 32A and 32B to turn the second transistors 32A and 32B off. The voltage comparison circuit units 52A, 52B, for example, short-circuit the gate terminal 32g and the source terminal 32s via the power supply voltage wiring 48 to set the gate voltages VG2A, VG2B of the second transistors 32A, 32B to 0 V, thereby turning the second transistors 32A, 32B to the OFF state. When the power supply of the semiconductor device 100 is turned off, the second transistors 32A, 32B turn off before the power supply voltage VDD becomes equal to the absolute value Vth of the threshold voltages of the first transistors 31A, 31B.

[0054] As described above, when the semiconductor device 100 is powered on, the control circuit units 50A, 50B turn on the second transistors 32A, 32B after the power supply voltage VDD exceeds the absolute value Vth of the threshold voltages of the first transistors 31A, 31B, and when the semiconductor device 100 is powered off, they turn off the second transistors 32A, 32B before the power supply voltage VDD becomes equal to or lower than the absolute value Vth of the threshold voltages of the first transistors 31A, 31B. This prevents the transistor circuits 30A, 30B from being turned on when the semiconductor device 100 is powered on and when the semiconductor device 100 is powered off, thereby preventing unintended current from flowing through the external load 60.

[0055] When the power supply voltage VDD drops to Vh when the semiconductor device 100 is turned off, the switching circuit units 51A and 51B turn off the fourth transistors 34A and 34B and the fifth transistors 35A and 35B. At this time, the switching circuit units 51A and 51B may keep the fourth transistors 34A and 34B in the on state.

[0056] At time t10, which is later than time t9, the power supply voltage VDD drops to the absolute value Vth of the threshold voltage of the first transistors 31A and 31B. When the power supply voltage VDD falls below the absolute value Vth of the threshold voltage of the first transistors 31A and 31B, the gate voltages VG1A and VG1B of the first transistors 31A and 31B rise above the threshold voltage, and the first transistors 31A and 31B turn on. As described above, because the second transistors 32A and 32B are in the off state before the power supply voltage VDD reaches the absolute value Vth, the transistor circuits 30A and 30B remain in the off state even when the first transistors 31A and 31B turn on. When the power supply voltage VDD falls to 0 V at time t11, the semiconductor device 100 stops operating.

[0057] Next, a description will be given of a current Is1 that flows when a voltage is applied between the drain terminal D and the source terminal S of the high-side transistor circuit 30A before the semiconductor device 100 is powered on. FIG. 6 is a diagram showing a current Is1 that flows through the high-side semiconductor package 10A when a voltage is applied between the drain terminal D and the source terminal S of the high-side transistor circuit 30A before the semiconductor device 100 is powered on. A case in which a voltage is applied between the drain terminal D and the source terminal S of the high-side transistor circuit 30A before the semiconductor device 100 is powered on refers to, for example, a case in which the power supply VDC is turned on before the semiconductor device 100 is powered on. In the following description, a case in which a voltage is applied between the drain terminal D and the source terminal S of the high-side transistor circuit 30A before the semiconductor device 100 is powered on will be described using startup of the power supply VDC as an example.

[0058] 6, when the power supply VDC is started, a current Is1 flows from the drain terminal D between the drain terminal 31d and the source terminal 31s of the first transistor 31A, which is in the ON state. The current Is1 flows from the source terminal 31s through the capacitor 44, the body diode of the fourth transistor 34A, the resistor element 43, and the diode 45, in that order, to the source terminal S of the transistor circuit 30A. At this time, the current Is1 flows through the resistor element 43, and the value of the current Is1 decreases according to the resistance value of the resistor element 43, thereby suppressing the occurrence of an inrush current when the power supply VDC is started. The current Is1 flows from the drain terminal D of the transistor circuit 30A through the drive circuit 40A and toward the source terminal S of the transistor circuit 30A.

[0059] Before the capacitor 44 is charged by the voltage applied between the drain terminal D and the source terminal S, a potential difference occurs between the electrodes of the capacitor 44, causing a current Is1 to flow through the capacitor 44. The current Is1 is generated until the capacitor 44 is charged.

[0060] Next, a description will be given of the current Is2 that flows when the high-side transistor circuit 30A is in the OFF state and the low-side transistor circuit 30B is switched from the ON state to the OFF state during the switching operation of the semiconductor device 100. Fig. 7 is a diagram showing the current Is2 that flows when the high-side transistor circuit 30A is in the OFF state and the low-side transistor circuit 30B is switched from the ON state to the OFF state.

[0061] As shown in FIG. 7, when the low-side transistor circuit 30B is switched to the OFF state, a current Is2 flows from the source terminal S of the transistor circuit 30A to the second transistor 32A. The current Is2 flows from the drain terminal 32d to the source terminal 32s of the second transistor 32A. The current Is2 that flows through the second transistor 32A flows from the source terminal 32s through the capacitor 44, the fourth transistor 34A, the fifth transistor 35A, and the gate-drain capacitance of the first transistor 31A in that order, and then to the drain terminal D of the transistor circuit 30A. At this time, the high-side transistor circuit 30A is in the OFF state, and the fourth transistor 34A and the fifth transistor 35A are in the ON state. Therefore, even if the current Is2 flows through the fourth transistor 34A and the fifth transistor 35A, a voltage drop is suppressed. This prevents the voltage at the gate terminal 31g of the first transistor 31A, which is connected to the source terminal 35s of the fifth transistor 35A, from dropping significantly, thereby preventing undershoot from occurring in the gate voltage VG1A of the first transistor 31A. The current Is2 flows from the source terminal S of the transistor circuit 30A through the drive circuit 40A and the gate terminal 31g of the first transistor 31A to the drain terminal D of the transistor circuit 30A.

[0062] As shown in FIG. 4, when the low-side transistor circuit 30B is turned off, a current Ie2 flows from the source terminal S to the drain terminal D of the high-side transistor circuit 30A. The current Ie2 also flows during the dead time immediately after the low-side transistor circuit 30B is turned off and before the high-side transistor circuit 30A is turned on. When the transistor circuit 30A is turned off, the first transistor 31A is also turned off. Therefore, the current Ie2 flowing through the first transistor 31A from the source terminal 31s to the drain terminal 31d flows through the body diode of the first transistor 31A. As a result, a forward voltage of the body diode is generated between the source terminal 31s and the drain terminal 31d of the first transistor 31A. This voltage causes a current Is2 to flow from the source terminal 31s to the drain terminal 31d of the first transistor 31A without passing through the body diode of the first transistor 31A. This current Is2 is generated until the capacitor 44 and the gate-drain capacitance of the first transistor 31A are charged.

[0063] In addition, when the high-side transistor circuit 30A is switched to the ON state from the state in which the current Ie2 flows during the dead time immediately after the low-side transistor circuit 30B is turned OFF and before the high-side transistor circuit 30A is turned ON, the first transistor 31A is turned ON, and the loss of the current Ie2 flowing through the first transistor 31A is reduced.

[0064] In the first embodiment, the path through which the above-described current Is1 flows is the first path 49a, and the path through which the above-described current Is2 flows is the second path 49b. When a voltage is applied between the drain terminal D and the source terminal S of the transistor circuit 30A before the semiconductor device 100 is powered on, the drive circuit 40A switches states such that the path through which the current Is1 flows is the first path 49a, and when the transistor circuit 30A and the transistor circuit 30B perform a switching operation, the path through which the current Is2 flows is the second path 49b when the transistor circuit 30B is turned off.

[0065] The resistance value of the first path 49a is equal to or greater than the resistance value of the resistive element 43. The resistance value of the first path 49a is the total resistance value while the current Is1 flows through the first path 49a from the drain terminal D of the transistor circuit 30A to the source terminal S of the transistor circuit 30A. In the first embodiment, the first path 49a includes the resistive element 43 and an element other than the resistive element 43, and therefore the resistance value of the first path 49a is greater than the resistance value of the resistive element 43.

[0066] The resistance value of the second path 49b from the source terminal S to the gate terminal 31g of the first transistor 31A is smaller than the resistance value of the resistive element 43 connected to the gate terminal 31g of the first transistor 31A. The resistance value of the second path 49b from the source terminal S to the gate terminal 31g of the first transistor 31A is the total resistance value while the current Is2 flows through the second path 49b from the source terminal S of the transistor circuit 30A to the gate terminal G of the transistor circuit 30A, i.e., the gate terminal 31g of the first transistor 31A.

[0067] FIG. 10 is a circuit diagram showing a portion of a semiconductor device 400 of Comparative Example 1. In the description of Comparative Example 1, the same components as those in the first embodiment may be denoted by the same reference numerals as appropriate and the description thereof may be omitted. As shown in FIG. 10, a drive circuit 440A of the semiconductor device 400 of Comparative Example 1 includes a diode 445 instead of the fifth transistor 35A in the semiconductor device 100 described above. The anode of the diode 445 is connected to the gate terminal 31g of the first transistor 31A. The cathode of the diode 445 is connected to the drain terminal 34d of the fourth transistor 34A.

[0068] In the semiconductor device 400 of Comparative Example 1, the current Is3 that flows when the low-side transistor circuit 30B is switched to the OFF state cannot flow through the diode 445. Instead, it flows through the resistor element 43 and then to the gate terminal 31g of the first transistor 31A. When the current Is3 flows through the resistor element 43, a voltage drop occurs, causing an undershoot in the gate voltage VG1A of the first transistor 31A. Therefore, in the semiconductor device 400 of Comparative Example 1, a Zener diode 446 is provided in the drive circuit 440A to suppress the undershoot in the gate voltage VG1A. The anode of the Zener diode 446 is connected to the gate terminal 31g of the first transistor 31A. The cathode of the Zener diode 446 is connected to the power supply voltage wiring 48. However, the Zener diode 446 has a limited response time, limiting its effectiveness in suppressing undershoot. Therefore, the semiconductor device 400 of Comparative Example 1 has a problem in that it is not possible to sufficiently suppress the undershoot occurring in the gate voltage VG1A of the first transistor 31A.

[0069] To address the above problem, according to the first embodiment, a drive circuit 40A is a drive circuit 40A that normally-off drives a transistor circuit 30A configured by serially connecting a normally-on first transistor 31A and a normally-off second transistor 32A. A power supply voltage line 48, to which a power supply voltage VDD is applied, is connected between the first transistor 31A and the second transistor 32A. The drive circuit 40A includes a diode 45 having an anode connected to the gate terminal (drive terminal) 31g of the first transistor 31A and a cathode connected to the drain terminal (output terminal) 32d of the second transistor 32A, a third transistor 33A arranged between a power supply voltage wiring 48 and the gate terminal 31g of the first transistor 31A, a fourth transistor 34A arranged between a ground 91 having a reference potential VSS that serves as a reference for the power supply voltage VDD and the gate terminal 31g of the first transistor 31A, a fifth transistor 35A arranged between the gate terminal 31g of the first transistor 31A and the fourth transistor 34A, and a control circuit unit 50A that switches each of the second transistor 32A, the third transistor 33A, the fourth transistor 34A, and the fifth transistor 35A between an ON state and an OFF state. Therefore, by keeping the fifth transistor 35A in the ON state when the low-side transistor circuit 30B is switched to the OFF state, the current Is2 flows from the power supply voltage line 48 to the fourth transistor 34A via the ground 91, and then flows through the fifth transistor 35A, which is in the ON state and has a lower resistance value than the resistive element 43, to the gate terminal 31g of the first transistor 31A, as shown in FIG. 7. This makes it possible to prevent a voltage drop from occurring until the current Is2 flows to the gate terminal 31g. This makes it possible to prevent undershoot from occurring in the gate voltage (drive voltage) VG1A of the first transistor 31A.

[0070] FIG. 11 is a circuit diagram showing a portion of a semiconductor device 500 of Comparative Example 2. In the description of Comparative Example 2, components similar to those of the first embodiment may be denoted by the same reference numerals as appropriate and their description may be omitted. As shown in FIG. 11, a drive circuit 540A in the semiconductor device 500 of Comparative Example 2 differs from the drive circuit 440A of the semiconductor device 400 of Comparative Example 1 in that it includes a sixth transistor 536. In the drive circuit 540A, the sixth transistor 536 forms an active Miller clamp circuit. The sixth transistor 536 is a normally-off transistor. The sixth transistor 536 is an N-channel field-effect transistor. A drain terminal 536d of the sixth transistor 536 is connected to the gate terminal 31g of the first transistor 31A and the anode of the diode 445. A source terminal 536s of the sixth transistor 536 is connected to ground 91. A gate terminal 536g of the sixth transistor 536 is connected to the switching circuit unit 51A. The sixth transistor 536 is switched between an ON state and an OFF state by the switching circuit section 51A.

[0071] In the drive circuit 540A of Comparative Example 2, turning on the sixth transistor 536 shorts the gate terminal 31g of the first transistor 31A to ground 91. Therefore, by turning on the sixth transistor 536 in synchronization with the timing at which the low-side transistor circuit 30B is switched off, the potential of the gate terminal 31g of the first transistor 31A can be set to the reference potential VSS, thereby preventing undershoot in the gate voltage VG1A. However, as shown in FIG. 11 , during startup of the power supply VDC, current Is4 flowing from the first transistor 31A to ground 91 flows through the resistor element 43 and the body diode of the sixth transistor 536, which has a smaller resistance value than the reverse resistance of the diode 445, and then flows from the diode 45 to the source terminal S of the transistor circuit 30A. Therefore, current Is4 does not flow through elements with a higher resistance value, and current Is4 cannot be reduced. Therefore, during startup of the power supply VDC, inrush current cannot be prevented. In this way, if the only purpose is to suppress undershoot, it is possible to provide an active Miller clamp circuit as in Comparative Example 2. However, in that case, there is a problem that the occurrence of inrush current cannot be suppressed.

[0072] To address the above problem, according to the first embodiment, the fifth transistor 35A is disposed between the gate terminal 31g of the first transistor 31A and the fourth transistor 34A. Therefore, as shown in FIG. 6 , unlike the sixth transistor 536 of Comparative Example 2, the current Is1 that flows during startup of the power supply VDC does not flow directly from ground 91 to the fifth transistor 35A. This allows the current Is1 to be reduced by, for example, disposing a resistive element such as the resistive element 43 between the time when the current Is1 flows from the first transistor 31A to ground 91 and the time when it flows to the source terminal S of the transistor circuit 30A. Therefore, the occurrence of inrush current during startup of the power supply VDC can be suppressed. As described above, according to the first embodiment, the occurrence of inrush current can be suppressed while suppressing undershoot in the gate voltage VG1A of the first transistor 31A.

[0073] Furthermore, according to the first embodiment, the control circuit unit 50A turns on the second transistor 32A when the voltage of the power supply voltage line 48 is higher than the absolute value Vth of the threshold voltage of the first transistor 31A, and turns on the fifth transistor 35A when the voltage of the power supply voltage line 48 is higher than the absolute value Vth of the threshold voltage of the first transistor 31A and the fourth transistor 34A is on. Therefore, when the drive circuit 40A is powered on and the voltage of the power supply voltage line 48 is a constant voltage Vd higher than the absolute value Vth of the threshold voltage of the first transistor 31A, the second transistor 32A is always on. In this state, when the third transistor 33A disposed between the power supply voltage line 48 and the gate terminal 31g of the first transistor 31A is turned on, the source terminal 31s and gate terminal 31g of the first transistor 31A are short-circuited via the power supply voltage line 48, and the normally-on first transistor 31A is turned on. This switches the transistor circuit 30A to the ON state. Meanwhile, when the fourth transistor 34A, which is disposed between the ground 91 and the gate terminal 31g of the first transistor 31A, is switched to the ON state, the source terminal 31s and gate terminal 31g of the first transistor 31A are short-circuited via the ground 91, and the normally-on first transistor 31A switches to the OFF state. Therefore, by switching the state of the third transistor 33A and the state of the fourth transistor 34A using the control circuit 50A, the state of the transistor circuit 30A can be easily switched. Furthermore, when the low-side transistor circuit 30B switches to the OFF state and the current Is2 described above starts to flow, the high-side transistor circuit 30A is also in the OFF state, and therefore the fourth transistor 34A is in the ON state. When the voltage of the power supply voltage wiring 48 is higher than the absolute value Vth of the threshold voltage of the first transistor 31A and the fourth transistor 34A is in the ON state, the control circuit unit 50A turns the fifth transistor 35A to the ON state, so that when the above-mentioned current Is2 flows, the fifth transistor 35A is also in the ON state along with the fourth transistor 34A.This makes it possible to prevent a voltage drop from occurring when the current Is2 flows through the fourth transistor 34A and the fifth transistor 35A, as described above, and to suitably prevent an undershoot from occurring in the gate voltage VG1A of the first transistor 31A.

[0074] Furthermore, according to the first embodiment, the drive circuit 40A includes a resistive element 43 disposed between the gate terminal 31g of the first transistor 31A and the third transistor 33A. Therefore, when the third transistor 33A is turned on and the power supply voltage wiring 48 and the gate terminal 31g of the first transistor 31A are short-circuited, the resistive element 43 can suppress a sudden current flow from the power supply voltage wiring 48 to the gate terminal 31g.

[0075] Furthermore, according to the first embodiment, the third transistor 33A and the fourth transistor 34A are connected in series. Therefore, when the power supply VDC is started, the current Is1 that flows through the fourth transistor 34A flows to the resistive element 43 that is disposed between the gate terminal 31g of the first transistor 31A and the third transistor 33A. This allows the current Is1 to be reduced by the resistive element 43, thereby preventing an inrush current from occurring. Furthermore, by connecting the third transistor 33A and the fourth transistor 34A, the connection terminal 21, which is connected to the resistive element 43 among the connection terminals of the semiconductor chip 20A, can be connected to the ground 91 via the fourth transistor 34A. This facilitates stabilization of the potential of the connection terminal 21.

[0076] According to the first embodiment, the drive circuit 40A includes a semiconductor chip 20A having a diode 45, a third transistor 33A, a fourth transistor 34A, a fifth transistor 35A, and a control circuit unit 50A. Therefore, by connecting the terminals of the semiconductor chip 20A to the transistor circuit 30A, a circuit that causes the transistor circuit 30A to operate normally can be easily configured. Furthermore, compared to providing the diode 45, the third transistor 33A, the fourth transistor 34A, the fifth transistor 35A, and the control circuit unit 50A as individual elements, the overall drive circuit 40A is more easily miniaturized, and the wiring connecting each element can be shortened, thereby reducing wiring resistance.

[0077] Furthermore, according to the first embodiment, the semiconductor device 100 includes a semiconductor package 10A in which the drive circuit 40A and the transistor circuit 30A are enclosed in a single package. Therefore, various circuits can be easily configured by regarding the entire semiconductor package 10A as a single normally-off transistor. Furthermore, compared to a case in which the drive circuit 40A and the transistor circuit 30A are provided as separate elements, the entire semiconductor device 100 is more easily miniaturized, and the length of the wiring connecting the elements can be shortened, thereby reducing wiring resistance.

[0078] Furthermore, according to the first embodiment, the semiconductor device 100 includes a half-bridge circuit 30H configured by connecting two transistor circuits 30A and 30B in series. Therefore, regardless of whether an operator configuring a circuit using the semiconductor device 100 uses the transistor circuit 30A or the transistor circuit 30B as the high-side transistor circuit, the occurrence of gate voltage undershoot and inrush current can be suppressed as described above. Furthermore, even in a circuit in which the transistor circuit 30A and the transistor circuit 30B are switched between the high side and the low side, the occurrence of gate voltage undershoot and inrush current can be suppressed as described above regardless of whether the transistor circuit 30A or the transistor circuit 30B is the high-side transistor circuit.

[0079] According to the first embodiment, the transistor circuit 30A functions as a transistor having a gate terminal 31g of the first transistor 31A, i.e., a gate terminal G (drive terminal), a drain terminal D (first terminal) provided in the first transistor 31A, and a source terminal S (second terminal) which is a drain terminal 32d (output terminal) of the second transistor 32A, and is connected in series to the transistor circuit 30B (switching element). The source terminal S is connected to the transistor circuit 30B. When a voltage is applied between the drain terminal D and the source terminal S of the semiconductor device 100 before the power supply of the semiconductor device 100 is turned on, the drive circuit 40A switches its state so that a path through which a current Is1 flows from the drain terminal D through the drive circuit 40A toward the source terminal S becomes the first path 49a. Also, when the transistor circuits 30A and 30B are switched, when the transistor circuit 30B is turned off, a path through which a current Is2 flows from the source terminal S through the drive circuit 40A and the gate terminal 31g of the first transistor 31A toward the drain terminal D becomes the second path 49b. The resistance value of the second path 49b from the source terminal S to the gate terminal 31g of the first transistor 31A is smaller than the resistance value of the resistive element 43 connected to the gate terminal 31g of the first transistor 31A. Therefore, compared to when the current Is2 flows through the resistive element 43, a voltage drop can be suppressed while the current Is2 flows through the second path 49b to the gate terminal 31g. Therefore, it is possible to prevent undershoot from occurring in the gate voltage (drive voltage) VG1A of the first transistor 31A. Furthermore, the resistance value of the first path 49a is equal to or greater than the resistance value of the resistive element 43. Therefore, the resistance value of the first path 49a can be made greater than that of a path provided with the resistive element 43, and the current Is1 flowing through the first path 49a can be made smaller. Therefore, it is possible to prevent inrush current from occurring when the power supply VDC is started up.

[0080] (Second embodiment) The second embodiment differs from the first embodiment in that the wiring portion between the third transistor 33A and the fourth transistor 34A is disconnected. In the following description, the same components as those in the above-described embodiments may be denoted by the same reference numerals as appropriate and the description thereof may be omitted.

[0081] FIG. 8 is a circuit diagram showing a portion of a semiconductor device 200 according to a second embodiment. As shown in FIG. 8, in a drive circuit 240A of the semiconductor device 200, a wiring portion 73 connecting the third transistor 33A and the resistive element 43 and a wiring portion 74 connecting the fourth transistor 34A and the fifth transistor 35A are insulated from each other. Therefore, a current Is5 flowing during startup of the power supply VDC flows through the first transistor 31A, the capacitor 44, and the fourth transistor 34A in this order, and then flows through the fifth transistor 35A instead of the resistive element 43. Before the semiconductor device 200 is powered on, the fifth transistor 35A is in an OFF state. Therefore, according to the second embodiment, the current Is5 flowing during startup of the power supply VDC can be significantly reduced by the fifth transistor 35A being in an OFF state. This further reduces the occurrence of inrush current during startup of the power supply VDC.

[0082] The current Is5 flows from the drain terminal D of the transistor circuit 30A through the drive circuit 240A to the source terminal S of the transistor circuit 30A. The path through which the current Is5 flows is the first path 249a. The resistance value of the first path 249a is equal to or greater than the resistance value of the resistive element 43. In the second embodiment, the first path 249a includes the fifth transistor 35A in the OFF state. The resistance value of the fifth transistor 35A in the OFF state is greater than the resistance value of the resistive element 43. Therefore, in the second embodiment, the resistance value of the first path 249a is greater than the resistance value of the resistive element 43.

[0083] Other configurations of the drive circuit 240A are similar to other configurations of the drive circuit 40A in Embodiment 1. Other configurations of the semiconductor device 200 are similar to other configurations of the semiconductor device 100 in Embodiment 1.

[0084] (Third embodiment) The third embodiment differs from the first embodiment in that the second transistor 332A is an N-channel transistor. In the following description, the same components as those in the above-described embodiments may be denoted by the same reference numerals as appropriate and the description thereof may be omitted.

[0085] 9 is a circuit diagram showing a portion of a semiconductor device 300 according to the third embodiment. As shown in FIG. 9, in a drive circuit 340A according to the third embodiment, a second transistor 332A of a transistor circuit 330A is an N-channel field-effect transistor. A drain terminal 332d of the second transistor 332A is connected to a source terminal 31s of the first transistor 31A. A source terminal 332s of the second transistor 332A is connected to a wiring portion 71. A cathode of a diode 45 is connected to the source terminal 332s of the second transistor 332A. In the third embodiment, the source terminal 332s of the second transistor 332A is the source terminal S of the transistor circuit 330A.

[0086] The drive circuit 340A has a level shifter circuit section 390. The level shifter circuit section 390 is connected to the gate terminal 332g and the source terminal 332s of the second transistor 332A. A second power supply voltage VDD2 is applied to the level shifter circuit section 390. The second power supply voltage VDD2 is a voltage higher than the power supply voltage VDD. In the third embodiment, a voltage comparison circuit section 352A of the control circuit section 350A outputs a comparison result of the power supply voltage VDD to the switching circuit section 51A and the level shifter circuit section 390.

[0087] When the level shifter circuit unit 390 receives a signal from the voltage comparison circuit unit 352A indicating that the power supply voltage VDD has exceeded the absolute value Vth of the threshold voltage of the first transistor 31A, the level shifter circuit unit 390 applies the second power supply voltage VDD2 to the gate terminal 332g of the second transistor 332A. This switches the second transistor 332A to an ON state. In the third embodiment, when the level shifter circuit unit 390 receives a signal from the voltage comparison circuit unit 352A indicating that the power supply voltage VDD has reached or exceeded a value Vh that is higher than the absolute value Vth of the threshold voltage of the first transistor 31A, the level shifter circuit unit 390 applies the second power supply voltage VDD2 to the gate terminal 332g of the second transistor 332A, switching the second transistor 332A to an ON state. When the power supply voltage VDD is lower than the value Vh, the level shifter circuit unit 390 short-circuits the gate terminal 332g and source terminal 332s of the second transistor 332A, for example, to switch the second transistor 332A to an OFF state.

[0088] During the switching operation of the semiconductor device 300, the timing at which the state of the second transistor 332A is switched is the same as the timing at which the state of the second transistor 32A is switched in the first embodiment. In the third embodiment, the states of the transistors are switched in the same way as in the first embodiment, thereby making it possible to suppress undershoot in the gate voltage VG1A of the first transistor 31A and inrush current, as in the above-described embodiments.

[0089] Other configurations of the drive circuit 340A are similar to other configurations of the drive circuit 40A in Embodiment 1. Other configurations of the semiconductor device 300 are similar to other configurations of the semiconductor device 100 in Embodiment 1.

[0090] According to at least one of the above-described embodiments, the drive circuit is a drive circuit that normally drives a transistor circuit configured by connecting a normally-on first transistor and a normally-off second transistor in series. A power supply voltage wiring, to which a power supply voltage is applied, is connected between the first transistor and the second transistor. The drive circuit includes: a diode having an anode connected to the drive terminal of the first transistor and a cathode connected to the output terminal of the second transistor; a third transistor disposed between the power supply voltage wiring and the drive terminal of the first transistor; a fourth transistor disposed between the drive terminal of the first transistor and a ground having a reference potential that serves as a reference for the power supply voltage; a fifth transistor disposed between the drive terminal of the first transistor and the fourth transistor; and a control circuit that switches each of the second transistor, the third transistor, the fourth transistor, and the fifth transistor between an ON state and an OFF state. This suppresses undershoot in the drive voltage of the first transistor.

[0091] The first transistor may be any transistor as long as it is a normally-on type transistor. The second transistor may be any transistor as long as it is a normally-off type transistor. The third transistor may be any transistor that is arranged between the power supply voltage wiring and the drive terminal of the first transistor and that can be switched on / off by the control circuit. The fourth transistor may be any transistor that is arranged between the ground having a reference potential that serves as the reference for the power supply voltage and the drive terminal of the first transistor and that can be switched on / off by the control circuit. The fifth transistor may be any transistor that is arranged between the drive terminal of the first transistor and the fourth transistor and that can be switched on / off by the control circuit.

[0092] The control circuit unit may have any configuration. The control circuit unit may be configured to switch voltages applied to the second transistor, the third transistor, the fourth transistor, and the fifth transistor using switching elements such as transistors, or may include a microprocessor or the like. The elements included in the semiconductor chip provided in the drive circuit are not particularly limited. The elements included in the semiconductor package provided in the semiconductor device are not particularly limited. The semiconductor device may be configured with only one semiconductor package. When a switching element is connected in series to a transistor circuit configured by connecting a normally-on first transistor and a normally-off second transistor in series according to the embodiment, the switching element may be any switching element. The switching element may have the same configuration as the transistor circuit according to the embodiment, or may have a different configuration from the transistor circuit according to the embodiment.

[0093] The driving circuit and the semiconductor device according to the embodiment include the following additional aspects. (Appendix 1) A drive circuit for normally-off driving a transistor circuit configured by connecting a normally-on first transistor and a normally-off second transistor in series, a power supply voltage wiring to which a power supply voltage is applied is connected between the first transistor and the second transistor; a diode having an anode connected to the drive terminal of the first transistor and a cathode connected to the output terminal of the second transistor; a third transistor disposed between the power supply voltage wiring and a drive terminal of the first transistor; a fourth transistor disposed between a ground having a reference potential that is a reference for the power supply voltage and a drive terminal of the first transistor; a fifth transistor disposed between the drive terminal of the first transistor and the fourth transistor; a control circuit unit that switches each of the second transistor, the third transistor, the fourth transistor, and the fifth transistor between an ON state and an OFF state; A drive circuit comprising: (Appendix 2) The control circuit unit When the voltage of the power supply voltage wiring is higher than the absolute value of the threshold voltage of the first transistor, the second transistor is turned on; 2. The drive circuit according to claim 1, wherein the fifth transistor is turned on when the voltage of the power supply voltage wiring is higher than the absolute value of the threshold voltage of the first transistor and the fourth transistor is in an on state. (Appendix 3) 3. The drive circuit of claim 1, further comprising a resistive element disposed between the drive terminal of the first transistor and the third transistor. (Appendix 4) 4. The drive circuit according to claim 3, wherein the third transistor and the fourth transistor are connected in series with each other. (Appendix 5) 4. The drive circuit according to claim 3, wherein a wiring section connecting the third transistor and the resistive element and a wiring section connecting the fourth transistor and the fifth transistor are insulated from each other. (Appendix 6) 6. The drive circuit according to claim 1, further comprising a semiconductor chip having the diode, the third transistor, the fourth transistor, the fifth transistor, and the control circuit unit. (Appendix 7) A drive circuit according to any one of Supplementary Note 1 to Supplementary Note 6; the transistor circuit being driven in a normally-off state by the drive circuit; A semiconductor device comprising: (Appendix 8) 8. The semiconductor device according to claim 7, further comprising a semiconductor package in which the drive circuit and the transistor circuit are enclosed in a single package. (Appendix 9) 9. The semiconductor device according to claim 7, further comprising a half-bridge circuit configured by connecting two of the transistor circuits in series with each other. (Appendix 10) The semiconductor device according to claim 7 or 8, the transistor circuit functions as a transistor having a drive terminal of the first transistor, a first terminal provided on the first transistor, and a second terminal which is an output terminal of the second transistor, and is connected in series to a switching element; the second terminal is connected to the switching element; The drive circuit When a voltage is applied between the first terminal and the second terminal before the semiconductor device is powered on, a path through which a current flows from the first terminal to the second terminal through the drive circuit becomes a first path, and when the transistor circuit and the switching element are switched, when the switching element is turned off, a state is switched so that a path through which a current flows from the second terminal to the first terminal through the drive circuit and the drive terminal of the first transistor becomes a second path, a resistance value of the second path between the second terminal and the drive terminal of the first transistor is smaller than a resistance value of a resistive element connected to the drive terminal of the first transistor; A semiconductor device, wherein a resistance value in the first path is equal to or greater than a resistance value of the resistive element. (Appendix 11) A semiconductor device comprising: a transistor circuit configured by connecting a normally-on first transistor and a normally-off second transistor in series; and a drive circuit that drives the transistor circuit in a normally-off state, the transistor circuit functions as a transistor having a drive terminal of the first transistor, a first terminal provided on the first transistor, and a second terminal which is an output terminal of the second transistor, and is connected in series to a switching element; the second terminal is connected to the switching element; The drive circuit When a voltage is applied between the first terminal and the second terminal before the semiconductor device is powered on, a path through which a current flows from the first terminal to the second terminal through the drive circuit becomes a first path, and when the transistor circuit and the switching element are switched, when the switching element is turned off, a state is switched so that a path through which a current flows from the second terminal to the first terminal through the drive circuit and the drive terminal of the first transistor becomes a second path, a resistance value of the second path between the second terminal and the drive terminal of the first transistor is smaller than a resistance value of a resistive element connected to the drive terminal of the first transistor; A semiconductor device, wherein a resistance value in the first path is equal to or greater than a resistance value of the resistive element.

[0094] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents. [Explanation of symbols]

[0095] 10A, 10B... semiconductor package, 20A, 20B... semiconductor chip, 30A, 330A... transistor circuit, 30B... transistor circuit (switching element), 30H... half-bridge circuit, 31g, G... gate terminal (drive terminal of first transistor), 31A, 31B... first transistor, 32d... drain terminal (output terminal of second transistor), 32A, 32B, 332A... second transistor, 33A, 33B... third transistor, 34A, 34B... fourth transistor, 35A, 35B... fifth transistor transistor, 40A, 40B, 240A, 340A...drive circuit, 43...resistance element, 45...diode, 48...power supply voltage wiring, 49a, 249a...first path, 49b...second path, 50A, 50B, 350A...control circuit section, 73, 74...wiring section, 91...ground, 100, 200, 300, 400, 500...semiconductor device, D...drain terminal (first terminal), S...source terminal (second terminal), VDD, VDDA, VDDB...power supply voltage, VSS, VSSA, VSSB...reference potential, Vth...absolute value of threshold voltage of first transistor

Claims

1. A drive circuit for normally-off driving a transistor circuit configured by serially connecting a normally-on first transistor and a normally-off second transistor, a power supply voltage wiring to which a power supply voltage is applied is connected between the first transistor and the second transistor; a diode having an anode connected to the drive terminal of the first transistor and a cathode connected to the output terminal of the second transistor; a third transistor disposed between the power supply voltage wiring and a drive terminal of the first transistor; a fourth transistor disposed between a ground having a reference potential that is a reference for the power supply voltage and a drive terminal of the first transistor; a fifth transistor disposed between the drive terminal of the first transistor and the fourth transistor; a control circuit unit that switches each of the second transistor, the third transistor, the fourth transistor, and the fifth transistor between an ON state and an OFF state; A drive circuit comprising:

2. The control circuit unit When the voltage of the power supply voltage wiring is higher than the absolute value of the threshold voltage of the first transistor, the second transistor is turned on; 2. The drive circuit according to claim 1, wherein the fifth transistor is turned on when the voltage of the power supply voltage line is higher than the absolute value of the threshold voltage of the first transistor and the fourth transistor is turned on.

3. 2. The drive circuit of claim 1, further comprising a resistive element disposed between the drive terminal of the first transistor and the third transistor.

4. The drive circuit according to claim 3 , wherein the third transistor and the fourth transistor are connected in series with each other.

5. 4. The drive circuit according to claim 3, wherein a wiring portion connecting said third transistor and said resistance element and a wiring portion connecting said fourth transistor and said fifth transistor are insulated from each other.

6. The drive circuit according to claim 1 , comprising a semiconductor chip having the diode, the third transistor, the fourth transistor, the fifth transistor, and the control circuit portion.

7. A drive circuit according to any one of claims 1 to 6; the transistor circuit being driven in a normally-off state by the drive circuit; A semiconductor device comprising:

8. 8. The semiconductor device according to claim 7, further comprising a semiconductor package in which the drive circuit and the transistor circuit are enclosed in a single package.

9. The semiconductor device according to claim 7 , further comprising a half-bridge circuit configured by connecting two of the transistor circuits in series with each other.

10. 8. The semiconductor device according to claim 7, the transistor circuit functions as a transistor having a drive terminal of the first transistor, a first terminal provided on the first transistor, and a second terminal which is an output terminal of the second transistor, and is connected in series to a switching element; the second terminal is connected to the switching element; The drive circuit When a voltage is applied between the first terminal and the second terminal before the semiconductor device is powered on, a path through which a current flows from the first terminal to the second terminal through the drive circuit becomes a first path, and when the transistor circuit and the switching element are switched, when the switching element is turned off, a state is switched so that a path through which a current flows from the second terminal to the first terminal through the drive circuit and the drive terminal of the first transistor becomes a second path, a resistance value of the second path between the second terminal and the drive terminal of the first transistor is smaller than a resistance value of a resistive element connected to the drive terminal of the first transistor; A semiconductor device, wherein a resistance value in the first path is equal to or greater than a resistance value of the resistive element.

11. A semiconductor device comprising: a transistor circuit configured by connecting a normally-on first transistor and a normally-off second transistor in series; and a drive circuit that drives the transistor circuit in a normally-off state, the transistor circuit functions as a transistor having a drive terminal of the first transistor, a first terminal provided on the first transistor, and a second terminal which is an output terminal of the second transistor, and is connected in series to a switching element; the second terminal is connected to the switching element; The drive circuit When a voltage is applied between the first terminal and the second terminal before the semiconductor device is powered on, a path through which a current flows from the first terminal to the second terminal through the drive circuit becomes a first path, and when the transistor circuit and the switching element are switched, when the switching element is turned off, a state is switched so that a path through which a current flows from the second terminal to the first terminal through the drive circuit and the drive terminal of the first transistor becomes a second path, a resistance value of the second path between the second terminal and the drive terminal of the first transistor is smaller than a resistance value of a resistive element connected to the drive terminal of the first transistor; A semiconductor device, wherein a resistance value in the first path is equal to or greater than a resistance value of the resistive element.

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