Gate Driver

Abstract

This gate driver, which is for driving an N-channel type transistor connected between a terminal for impressing an input voltage and a terminal for impressing a switch voltage, comprises: a capacitor circuit that is connected between a terminal for impressing a boot voltage that is higher than the switch voltage by the voltage between the terminals of a boot capacitor and the terminal for impressing the switch voltage; and a timing control circuit that, after input gate capacity of the transistor has been precharged by the input voltage during an on-transition of the transistor, charges the input gate capacity with the boot voltage and lowers the capacity value of the capacitor circuit after an on-transition of the transistor.

Description

[Technical field]

[0001] The invention disclosed herein relates to a gate driver. [Background technology]

[0002] Conventionally, gate drivers that receive a boot voltage from a bootstrap circuit and drive an N-channel transistor (e.g., a metal oxide semiconductor field effect transistor [MOSFET] or an insulated gate bipolar transistor [IGBT]) have been widely used (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2004-304527 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, if the boot capacitor has a small capacity, it becomes difficult to maintain the boot voltage at a desired value, which may cause problems in driving the gates of the transistors.

[0005] In view of the above-mentioned problems discovered by the inventors of the present application, the invention disclosed in this specification aims to provide a gate driver that is unlikely to cause problems in driving the gate of a transistor even if the boot capacitor has a small capacity. [Means for solving the problem]

[0006] For example, the gate driver disclosed in this specification is a gate driver that drives an N-channel transistor connected between an input voltage application terminal and a switch voltage application terminal, and has a configuration (first configuration) including: a capacitor circuit connected between an application terminal of a boot voltage that is higher than the switch voltage by the voltage across a boot capacitor and the application terminal of the switch voltage; and a timing control circuit that precharges an input gate capacitance of the transistor with the input voltage when the transistor turns on, and then charges the input gate capacitance with the boot voltage, and reduces the capacitance value of the capacitor circuit after the transistor turns on.

[0007] The gate driver having the above first configuration may further include a first internal switch connected between the input voltage application terminal and the gate of the transistor, a second internal switch connected between the gate of the transistor and the switch voltage application terminal, and a third internal switch connected between the boot voltage application terminal and the gate of the transistor, and the timing control circuit may be configured to control the switching timing of the first internal switch, the second internal switch, and the third internal switch (second configuration).

[0008] Furthermore, in the gate driver having the above second configuration, the capacitor circuit may include a first capacitor having a first end connected to an application end of the boot voltage, a second capacitor having a first end connected to an application end of the switch voltage, a fourth internal switch connected between a second end of the first capacitor and the application end of the switch voltage, a fifth internal switch connected between the second end of the first capacitor and the second end of the second capacitor, and a sixth internal switch connected between the application end of the boot voltage and the second end of the second capacitor, and the timing control circuit may be configured to control the switching timing of the fourth internal switch, the fifth internal switch, and the sixth internal switch (third configuration).

[0009] Furthermore, in the gate driver having the above-described third configuration, the timing control circuit may be configured (fourth configuration) to sequentially switch between a first drive phase in which the first internal switch, the third internal switch, and the fifth internal switch are turned off and the second internal switch, the fourth internal switch, and the sixth internal switch are turned on, a second drive phase in which the second internal switch, the third internal switch, and the fifth internal switch are turned off and the first internal switch, the fourth internal switch, and the sixth internal switch are turned on, a third drive phase in which the first internal switch, the second internal switch, and the fifth internal switch are turned off and the third internal switch, the fourth internal switch, and the sixth internal switch are turned on, and a fourth drive phase in which the first internal switch, the second internal switch, the fourth internal switch, and the sixth internal switch are turned off and the third internal switch and the fifth internal switch are turned on.

[0010] In addition, in the gate driver having any one of the second to fourth configurations, the first internal switch may be configured (fifth configuration) to include an NDMOSFET having a drain connected to the application terminal of the input voltage, and an NMOSFET having a source connected to the source of the NDMOSFET and a drain connected to the gate of the transistor.

[0011] In addition, in the gate driver having the above-mentioned fifth configuration, the timing control circuit may be configured (sixth configuration) to turn on the NMOSFET before turning on the NDMOSFET and to turn off the NMOSFET before turning on the third internal switch.

[0012] In the gate driver having any one of the second to sixth configurations, the third internal switch may be a PDMOSFET (seventh configuration).

[0013] Furthermore, for example, the semiconductor device disclosed in this specification may have a configuration (eighth configuration) in which gate drivers having any one of the first to seventh configurations are integrated.

[0014] In addition, the semiconductor device having the eighth configuration may be configured (ninth configuration) by further integrating a boot capacitor connected between the boot voltage application terminal and the switch voltage application terminal.

[0015] In addition, the semiconductor device having the eighth or ninth configuration may be further configured (tenth configuration) by integrating an N-channel transistor connected between the input voltage application terminal and the switch voltage application terminal. Effect of the Invention

[0016] According to the invention disclosed in this specification, it is possible to provide a gate driver that is unlikely to cause a problem in driving the gate of a transistor even if the boot capacitor has a small capacity. [Brief description of the drawings]

[0017] [Figure 1] Diagram showing the overall configuration of a switching power supply [Diagram 2] FIG. 1 shows an example of a configuration of an upper driver. [Diagram 3] FIG. 1 is a diagram showing an example of a configuration of a capacitor circuit; [Figure 4] A diagram showing an example of a driving phase [Diagram 5] A diagram showing the switch switching state for each driving phase [Figure 6] A diagram showing the rising behavior of the switch voltage and the boot voltage. [Figure 7] FIG. 1 is a diagram showing an example of a configuration of an internal switch and a timing control circuit; [Figure 8] Diagram showing the vertical cross section of an NMOSFET [Figure 9] FIG. 1 is a diagram showing an example of an operation of a timing control circuit; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] <Switching power supply> 1 is a diagram showing the overall configuration of a switching power supply. The switching power supply 1 of this configuration example is a step-down DC / DC converter that steps down an input voltage Vi to generate a desired output voltage Vo, and includes a semiconductor device 100 and discrete components (in this diagram, an inductor L and a capacitor C are exemplified) that are externally attached to the semiconductor device 100.

[0019] The semiconductor device 100 is an entity (a so-called power supply control IC) that comprehensively controls the operation of the switching power supply 1, and has multiple external terminals (in this figure, a PVIN pin, a SW pin, and a GND pin are shown as examples) as a means of establishing electrical connection with the outside of the device.

[0020] The PVIN pin (power supply terminal) is connected to the application terminal of the input voltage Vi. The SW pin (switch terminal) is connected to the first terminal of the inductor L. The second terminal of the inductor L and the first terminal of the capacitor C are connected to the application terminal of the output voltage Vo. The GND pin (ground terminal) and the second terminal of the capacitor C are connected to the ground terminal. The inductor L and capacitor C connected in this manner function as a rectifying and smoothing circuit that rectifies and smoothes the square-wave-shaped switch voltage Vsw that appears at the SW pin to generate the output voltage Vo.

[0021] <Semiconductor device> Continuing to describe the internal configuration of the semiconductor device 100, with reference to Fig. 1. The semiconductor device 100 of this configuration example is configured by integrating an upper transistor 10H, a lower transistor 10L, an upper driver 20H, a lower driver 20L, an upper level shifter 30H, a lower level shifter 30L, a logic circuit 40, a boot capacitor Cb, and an internal switch SW0.

[0022] The upper transistor 10H is a semiconductor element that functions as an upper switch (output transistor) of the half-bridge output stage connected between the PVIN pin and the GND pin, and an NMOSFET is used in this diagram. Specifically, the drain of the upper transistor 10H is connected to the PVIN pin. The source of the upper transistor 10H is connected to the SW pin. The gate of the upper transistor 10H is connected to the output terminal (= application terminal of the upper gate drive signal HG) of the upper driver 20H.

[0023] The upper transistor 10H is turned on when the upper gate drive signal HG is at a high level (=Vb) and is turned off when the upper gate drive signal HG is at a low level (=Vsw).

[0024] The upper transistor 10H is accompanied by a gate-drain parasitic capacitance Cgd, a gate-source parasitic capacitance Cgs, and a drain-source parasitic capacitance Cds. The sum of the gate-drain parasitic capacitance Cgd and the gate-source parasitic capacitance Cgs corresponds to the input gate capacitance Ciss (=Cgd+Cgs) of the upper transistor 10H. Meanwhile, the sum of the drain-source parasitic capacitance Cds and the gate-drain parasitic capacitance Cgd corresponds to the output gate capacitance Coss (=Cds+Cgd) of the upper transistor 10H. The gate-drain parasitic capacitance Cgd corresponds to the feedback gate capacitance Crss (=Cgd) of the upper transistor 10H.

[0025] The lower transistor 10L is a semiconductor element that functions as the lower switch (synchronous rectification transistor) of the half-bridge output stage described above, and an NMOSFET is used in this diagram. Specifically, the connection relationship is that the drain of the lower transistor 10L is connected to the SW pin. The source of the lower transistor 10L is connected to the GND pin. The gate of the lower transistor 10L is connected to the output terminal (= application terminal of the lower gate drive signal LG) of the lower gate driver 20L.

[0026] The lower transistor 10L is turned on when the lower gate drive signal LG is at a high level (=Vi) and is turned off when the lower gate drive signal LG is at a low level (=GND).

[0027] However, the rectification method of the switching power supply 1 is not necessarily limited to the synchronous rectification method, and a diode rectification method may be adopted. In that case, instead of the lower transistor 10L, a diode with a cathode connected to the SW pin and an anode connected to the GND pin may be built in or attached externally.

[0028] The upper driver 20H receives the upper gate control signal HS and outputs the upper gate drive signal HG. Basically, the upper driver 20H sets the upper gate drive signal HG to a high level (=Vb) when the upper gate control signal HS is at a high level (=Vb), and sets the upper gate drive signal HG to a low level (=Vsw) when the upper gate control signal HS is at a low level (=Vsw).

[0029] In addition, with regard to the upper driver 20H, various measures (such as a precharge function using the input voltage Vi and a boot voltage maintenance function using a capacitor circuit, details of which will be described later) have been implemented to ensure that the gate drive of the upper transistor 10H is not hindered even if the boot capacitor Cb has a small capacity.

[0030] The lower driver 20L receives the lower gate control signal LS and outputs the lower gate drive signal LG. Basically, the lower driver 20L sets the lower gate drive signal LG to a high level (=Vi) when the lower gate control signal LS is a high level (=Vi), and sets the lower gate drive signal LG to a low level (=GND) when the lower gate control signal LS is a low level (=GND).

[0031] The upper level shifter 30H shifts the level of the upper logic signal HS0 (for example, LV-GND) to generate an upper gate control signal HS (for example, Vb-Vsw).

[0032] The lower level shifter 30L shifts the level of the lower logic signal LS0 (for example, LV-GND) to generate a lower gate control signal LS (for example, Vi-GND).

[0033] The logic circuit 40 generates an upper logic signal HS0 and a lower logic signal LS0 so that a desired output voltage Vo is generated from an input voltage Vi. Note that the feedback control method for the output voltage Vo can be any well-known technique (such as voltage mode control, current mode control, hysteresis control (ripple control) etc.), and therefore a detailed description thereof will be omitted.

[0034] The boot capacitor Cb is connected between the application end of the boot voltage Vb and the SW pin (=the application end of the switch voltage Vsw).

[0035] The internal switch SW0 is connected between the application end of the boot voltage Vb and the PVIN pin (=application end of the input voltage Vi). For example, the internal switch SW0 is turned on during the on period of the lower transistor 10L (=low level period of the switch voltage Vsw) and turned off during the on period of the upper transistor 10H (=high level period of the switch voltage Vsw). The internal switch SW0 may be connected between the application end of the boot voltage Vb and the application end of the internal power supply voltage VREF (for example, 5V).

[0036] The boot capacitor Cb and the internal switch SW0 connected in this manner form a bootstrap circuit that generates a boot voltage Vb that is higher than the switch voltage Vsw by the voltage across the boot capacitor Cb.

[0037] Incidentally, as shown in this figure, if the boot capacitor Cb is built into the semiconductor device 100, it is possible to reduce the number of external discrete components. However, it is difficult to ensure a sufficient capacitance value for the IC-built-in boot capacitor Cb (for example, it is assumed that the capacitance value is about five times the input gate capacitance Ciss associated with the upper transistor 10H).

[0038] Therefore, if no special measures are taken in the upper driver 10H, when the upper transistor 10H turns on, the charge stored in the boot capacitor Cb will be absorbed by the charge in the input gate capacitance Ciss, causing the boot voltage Vb to drop and causing problems in driving the gate of the upper transistor 10H.

[0039] In consideration of such considerations, various measures have been taken with respect to the upper driver 10H so that even if the boot capacitor Cb has a small capacity, the gate drive of the upper transistor 10H is unlikely to be hindered. Therefore, the upper driver 20H will be described in detail below.

[0040] <Upper driver> 2 is a diagram showing an example of the configuration of the high-side driver 20H. The high-side driver 20H of this example configuration includes internal switches SW1 to SW3, a capacitor circuit 21, and a timing control circuit 22.

[0041] The internal switch SW1 is connected between an application terminal of the input voltage Vi and an application terminal of the upper gate drive signal HG (=the gate of the upper transistor 10H), and is turned on / off in response to a switch control signal S1.

[0042] The internal switch SW2 is connected between the application terminal of the high-side gate drive signal HG and the application terminal of the switch voltage Vsw, and is turned on / off in response to a switch control signal S2.

[0043] The internal switch SW3 is connected between the application terminal of the boot voltage Vb and the application terminal of the high-side gate drive signal HG, and is turned on / off in response to a switch control signal S3.

[0044] The capacitor circuit 21 is connected between an application terminal of the boot voltage Vb and an application terminal of the switch voltage Vsw, and its capacitance value C21 is switched in response to a switch control signal S4. The capacitor circuit 21 includes a plurality of capacitors and internal switches (neither of which are shown), and the internal configuration thereof will be described later.

[0045] The timing control circuit 22 receives the upper gate control signal HS and generates the switch control signals S1 to S4, respectively, to control the on / off switching timing of the internal switches SW1 to SW3 and the capacitance value switching timing of the capacitor circuit 22.

[0046] For example, the timing control circuit 22 may generate the switch control signals S1 to S4 so as to precharge the input gate capacitance Ciss of the upper transistor 10H with the input voltage Vi (SW1 on, SW2 off, SW3 off) when the upper transistor 10H transitions to on, and then charge the input gate capacitance Ciss with the boot voltage Vb (SW1 off, SW2 off, SW3 on), and reduce the capacitance value C21 of the capacitor circuit 21 after the upper transistor 10H transitions to on.

[0047] With this type of internal switch control, even if the boot capacitor Cb has a small capacity, the drop in the boot voltage Vb that accompanies the on transition of the upper transistor 10H can be suppressed, making it less likely that problems will occur in driving the gate of the upper transistor 10H (details will be described later).

[0048] <Capacitor circuit> 3 is a diagram showing an example of the configuration of the capacitor circuit 21. The capacitor circuit 21 of this example is a so-called doubler capacitor (voltage doubler), and includes capacitors C1 and C2, a delay stage DLY, and internal switches SW4 to SW6.

[0049] The capacitor C1 has a first terminal connected to a terminal to which the boot voltage Vb is applied.

[0050] The capacitor C2 has a first terminal connected to the application terminal of the switch voltage Vsw.

[0051] The delay stage DLY generates the switch control signals S44, S45, and S46 by providing an appropriate delay to the switch control signal S4. The delay stage DLY may also invert the logic level of the switch control signal S4 as necessary. For example, an inverter stage in which a plurality of inverters are connected in series may be used as the delay stage DLY, and the output terminals of the inverters that output the switch control signals S44, S45, and S46, among the plurality of inverters, may be connected to the control terminals (gates) of the internal switches SW4, SW5, and SW6, respectively.

[0052] The internal switch SW4 (e.g., an NMOSFET) is connected between the second terminal of the capacitor C1 and the application terminal of the switch voltage Vsw, and is turned on / off in response to a switch control signal S44 (e.g., a delayed signal of the switch control signal S4). For example, the internal switch SW4 is turned on when the switch control signal S44 is at a high level, and turned off when the switch control signal S44 is at a low level.

[0053] The internal switch SW5 (e.g., an NMOSFET) is connected between the second end of the capacitor C1 and the second end of the capacitor C2, and is turned on / off in response to a switch control signal S45 (e.g., a signal obtained by further delaying the switch control signal S44). For example, the internal switch SW5 is turned on when the switch control signal S45 is at a high level, and turned off when the switch control signal S45 is at a low level.

[0054] The internal switch SW6 (e.g., a PDMOSFET) is connected between the application terminal of the boot voltage Vb and the second terminal of the capacitor C2, and is turned on / off in response to a switch control signal S46 (e.g., a signal obtained by delaying and logically inverting the switch control signal S4). For example, the internal switch SW6 is turned off when the switch control signal S46 is at a high level, and turned on when the switch control signal S46 is at a low level.

[0055] In this manner, the on / off switching timing of each of the internal switches SW4 to SW6 is controlled in response to the switch control signal S4 input from the timing control circuit 22.

[0056] In particular, the capacitor circuit 21 of this configuration example can take, as its operating states, a first operating state in which the internal switches SW4 and SW6 are on and the internal switch SW5 is off, and a second operating state in which the internal switches SW4 and SW6 are off and the internal switch SW5 is on. Each operating state will be described in detail below.

[0057] First, consider the first operating state in which the internal switches SW4 and SW6 are turned on and the internal switch SW5 is turned off. In this case, the capacitors C1 and C2 are connected in parallel between the application terminal of the boot voltage Vb and the application terminal of the switch voltage Vsw. Therefore, the capacitance value C21 of the capacitor circuit 21 is C21=C1+C2. In the first operating state, the capacitors C1 and C2 are charged in parallel.

[0058] Next, consider a case where the first operating state transitions to a second operating state in which the internal switches SW4 and SW6 are turned off and the internal switch SW5 is turned on. In this case, the capacitors C1 and C2 are connected in series between the application terminal of the boot voltage Vb and the application terminal of the switch voltage Vsw. Therefore, the capacitance value C21 of the capacitor circuit 21 is reduced to C21=(C1·C2) / (C1+C2).

[0059] At this time, the capacitors C1 and C2 each hold the charge stored in the first operating state. Therefore, if the voltage across each of the capacitors C1 and C2 immediately before the transition to the second operating state is VC, the boot voltage Vb is raised from (VC+Vsw) to (2VC+Vsw) immediately after the transition from the first operating state to the second operating state. In other words, the voltage across each of the capacitors VC is doubled.

[0060] Note that, while the boot voltage Vb can be raised higher as the capacitance value of each of the capacitors C1 and C2 is increased, the layout area occupied by the chip of the semiconductor device 100 increases. Therefore, taking into consideration the trade-off between the two, it is desirable to set the capacitance values ​​of the capacitors C1 and C2 so that, for example, the capacitance value C21 (=(C1·C2) / (C1+C2)) of the capacitor circuit 21 in the second operating state (=the state in which the capacitors C1 and C2 are connected in series) is approximately half the input gate capacitance Ciss.

[0061] Of course, the configuration of the capacitor circuit 21 is not necessarily limited to the above, and may be any configuration that can realize m-fold boost of the voltage VC between both ends (where m>1).

[0062] <Internal switch control> Next, the on / off switching control of the internal switches S1 to S6 by the timing control circuit 22 will be described in detail with reference to the drawings.

[0063] FIG. 4 is a diagram showing an example of drive phases in internal switch control, depicting the relationship between the switch voltage Vsw and drive phases (1) to (4). In this diagram, drive phase (1) from time t1 to t2 corresponds to the low-level period of the switch voltage Vsw. Drive phase (2) from time t3 to t4 corresponds to the rise period (first half) of the switch voltage Vsw. Drive phase (3) from time t4 to t5 corresponds to the rise period (second half) of the switch voltage Vsw. Drive phase (4) from time t5 to t6 corresponds to the high-level period of the switch voltage Vsw.

[0064] 5 is a diagram showing the on / off switching states of the internal switches SW0 to SW6 in the above drive phases (1) to (4). Note that the internal switch SW0 is not necessarily on / off controlled by the timing control circuit 22, but for convenience of explanation, in this figure it is treated in the same manner as the internal switches SW1 to SW6.

[0065] First, in the drive phase (1) (=time t1 to t2) corresponding to the low-level period of the switch voltage Vsw, the internal switch SW0 is turned on, and conduction is established between the application terminal of the boot voltage Vb and the PVIN pin (=application terminal of the input voltage Vi). As a result, the boot capacitor Cb is charged until the voltage across it almost matches the input voltage Vi.

[0066] In the drive phase (1), the timing control circuit 22 turns off the internal switches SW1 and SW3 and turns on the internal switch SW2. Therefore, the upper gate drive signal HG goes to a low level (=Vsw), and the upper transistor 10H is fully turned off.

[0067] In addition, in the driving phase (1), the timing control circuit 22 turns off the internal switch SW5 and turns on the internal switches SW4 and SW6. Therefore, the capacitors C1 and C2 are connected in parallel, and the capacitance C21 of the capacitor circuit 21 becomes C21=(C1+C2).

[0068] Next, in the drive phase (2) (=times t3 to t4) corresponding to the rising period (first half) of the switch voltage Vsw, the internal switch SW0 is turned off, and the connection between the application terminal of the boot voltage Vb and the PVIN pin is cut off. At this time, the charge stored in the previous drive phase (1) is held in the boot capacitor Cb. As a result, as the switch voltage Vsw rises, the boot voltage Vb rises to a voltage value (≒Vsw+Vin) that is higher than the switch voltage Vsw by the voltage between both ends of the boot capacitor Cb (≒Vi).

[0069] In the drive phase (2), the timing control circuit 22 turns off the internal switches SW2 and SW3 and turns on the internal switch SW1. Therefore, conduction is established between the application terminal of the input voltage Vi and the application terminal of the upper gate drive signal HG, so that the input gate capacitance Ciss of the upper transistor 10H is precharged by the input voltage Vi.

[0070] In the driving phase (2), the timing control circuit 22 turns off the internal switch SW5 and keeps the internal switches SW4 and SW6 on, as in the previous driving phase (1). Therefore, the capacitors C1 and C2 are maintained in a parallel connection state.

[0071] Next, in driving phase (3) (=times t4 to t5) corresponding to the rising period (second half) of the switch voltage Vsw, the internal switch SW0 remains turned off, following the previous driving phase (2).

[0072] In the drive phase (3), the timing control circuit 22 turns off the internal switches SW1 and SW2 and turns on the internal switch SW3. Therefore, conduction is established between the application terminal of the boot voltage Vb and the application terminal of the upper gate drive signal HG, so that the input gate capacitance Ciss of the upper transistor 10H is charged using the boot voltage Vb.

[0073] In the driving phase (3), the timing control circuit 22 turns off the internal switch SW5 and keeps the internal switches SW4 and SW6 on, as in the driving phases (1) and (2) described above. Therefore, the capacitors C1 and C2 are maintained in a parallel connection state.

[0074] Next, in driving phase (4) (=times t5 to t6) corresponding to the high-level period of the switch voltage Vsw, the internal switch SW0 remains off, following the previous driving phases (2) and (3).

[0075] In the drive phase (4), the timing control circuit 22 turns off the internal switches SW1 and SW2 and keeps the internal switch SW3 on, as in the drive phase (3) described above. Therefore, the upper gate drive signal HG goes to a high level (=Vb), and the upper transistor 10H is fully turned on.

[0076] In addition, in the driving phase (4), the timing control circuit 22 turns off the internal switches SW4 and SW6 and turns on the internal switch SW5. Therefore, the capacitors C1 and C2 are connected in series, and the capacitance C21 of the capacitor circuit 21 is reduced to C21=(C1·C2) / (C1+C2). As a result, it is possible to suppress the reduction in the boot voltage Vb caused by the charging of the input gate capacitance Ciss.

[0077] 6 is a diagram showing the rising behavior of each of the switch voltage Vsw and the boot voltage Vb. Note that times t3 to t5 in this diagram correspond to the above-mentioned times t3 to t5.

[0078] As explained above, during the rising period (first half) of the switch voltage Vsw from time t3 to t4, the input gate capacitance Ciss is precharged using the input voltage Vi. Then, during the rising period (second half) of the switch voltage Vsw from time t4 to t5, the remainder of the input gate capacitance Ciss is charged using the boot voltage Vb. Note that the rising slopes of the switch voltage Vsw and the boot voltage Vb from time t3 to t4 and from time t4 to t5 vary depending on the on-resistances of the internal switches SW3 and SW4.

[0079] In addition, during the high-level period of the switch voltage Vsw from time t5 onwards, the capacitance value C21 of the capacitor circuit 21 is reduced, thereby suppressing the decrease in the boot voltage Vb associated with the charging of the input gate capacitance Ciss (compare the solid line and dashed line of the boot voltage Vb).

[0080] In this manner, with the upper driver 20H of this configuration example, even if the boot capacitor Cb has a small capacity, the gate-source voltage Vgs of the upper transistor 10H can be secured while suppressing a decrease in the boot voltage Vb. Therefore, the upper transistor 10H can be reliably turned on, which reduces the on-resistance value of the upper transistor 10H and contributes to improving efficiency.

[0081] <Internal switch and timing control circuit> FIG. 7 is a diagram showing an example of the configuration of the internal switches SW1 to SW3 and the timing control circuit 22. As shown in FIG.

[0082] The internal switch SW1 includes an N-channel double-diffused MOS field effect transistor N1 (NDMOSFET [double-diffused MOSFET]) and an N-channel MOS field effect transistor N2 (NMOSFET). The internal switches SW2 and SW3 are NMOSFETs and PDMOSFETs, respectively.

[0083] The drain of the transistor N1 is connected to an application terminal of the input voltage Vi. The sources of the transistors N1 and N2 are connected to each other. The drain of the transistor N2 is connected to an application terminal of the upper gate drive signal HG (=the gate of the upper transistor 10H). The gates of the transistors N1 and N2 are connected to application terminals of the switch control signals S11 and S12 (corresponding to the above-mentioned switch control signal S1).

[0084] The transistor N1 is turned on when the switch control signal S11 is at a high level (=Vb) and turned off when the switch control signal S11 is at a low level (=Vsw). The transistor N2 is turned on when the switch control signal S12 is at a high level (=Vb) and turned off when the switch control signal S12 is at a low level (=Vsw).

[0085] The transistors N1 and N2 are associated with body diodes BD1 and BD2, each of which has its drain as a cathode and its source as an anode.

[0086] Generally, DMOSFETs are advantageous over MOSFETs in terms of higher voltage resistance, lower on-resistance, larger current capability, and higher speed, etc. Therefore, it is desirable to use the transistor N1, which is an NDMOSFET, as the internal switch SW1.

[0087] However, if transistor N1 is used alone as the internal switch SW1, when a reverse bias is applied to transistor N1 (=SW3 is on), a current flows through body diode BD1 from the terminal to which the upper gate drive voltage HG is applied to the terminal to which the input voltage Vi is applied, and some of this current flows into the p-type substrate as a sub-leakage current, causing the substrate potential to rise.

[0088] Therefore, the internal switch SW1 includes, in addition to the transistor N1 (NDMOSFET), a transistor N2 (NMOSFET) connected in series and in the reverse direction to the transistor N1. With this configuration, the body diode BD2 of the transistor N2 can cut off the sub-leakage current when a reverse bias is applied, making it possible to suppress the substrate potential from floating up.

[0089] 8 is a diagram showing a vertical cross section of an NMOSFET used as transistor N2. NMOSFET 300 has p-type substrate 301, n-type well 302, n+ type semiconductor region 303, p-type well 304, n+ type semiconductor region 305, n+ type semiconductor region 306, p+ type semiconductor region 307, n- type semiconductor regions 308 and 309, gate oxide film 310, and gate electrode 311.

[0090] The n-type well 302 is formed in the p-type substrate 301. A boot voltage Vb is applied to the n-type well 302 via an n+ type semiconductor region 303. Therefore, the n-type well 302 functions as a buried layer BL for electrically isolating the p-type substrate 301 and the p-type well 304 from each other.

[0091] The n+ type semiconductor region 303 is formed on the surface (outer periphery) of the n-type well 302, and functions as a contact for applying the boot voltage Vb.

[0092] The p-type well 304 is formed on the surface of the n-type well 302 (in a region surrounded by the n+ type semiconductor region 303), and functions as a back gate (BG) of the NMOSFET 300.

[0093] The n+ type semiconductor region 305 is formed on the surface of the p-type well 304 and functions as the drain (D) of the NMOSFET 300.

[0094] The n + type semiconductor region 306 is formed on the surface of the p-type well 304 at a position spaced a predetermined distance from the n + type semiconductor region 305 , and functions as the source (S) of the NMOSFET 300 .

[0095] The p+ type semiconductor region 307 is formed on the surface (outer periphery) of the p-type well 304, and functions as a contact for the back gate (BG).

[0096] The n− type semiconductor region 308 is formed on the surface of the p type well 304 from a position adjacent to the n+ type semiconductor region 305 to a position just below the outer edge of the gate oxide film 310 .

[0097] The n− type semiconductor region 309 is formed on the surface of the p type well 304 from a position adjacent to the n+ type semiconductor region 306 to a position just below the outer edge of the gate oxide film 310 .

[0098] A gate oxide film 310 is formed on the surface of the p-type well 304 .

[0099] The gate electrode 311 is formed on the surface of the gate oxide film 310 .

[0100] It should be noted that the NMOSFET 300 has parasitic capacitors p1 to p7 and parasitic diodes p8 to p10 associated with each portion thereof.

[0101] More specifically, parasitic capacitors p1 to p3 are respectively associated between the gate oxide film 310 and the n+ type semiconductor region 305, between the gate oxide film 310 and the n+ type semiconductor region 306, and between the gate oxide film 310 and the p-type well 304. Parasitic capacitors p4 and p5 are respectively associated between the p-type well 304 and the n+ type semiconductor region 305, and between the p-type well 304 and the n+ type semiconductor region 306. Parasitic capacitors p6 and p7 are respectively associated between the n-type well 302 and the p-type well 304, and between the n-type well 302 and the p-type substrate 301.

[0102] On the other hand, a parasitic diode p8 is associated between the n+ type semiconductor region 305 and the p-type well 304. The parasitic diode p8 has the n+ type semiconductor region 305 as a cathode and the p-type well 304 as an anode. A parasitic diode p9 is associated between the n-type well 302 and the p-type well 304. The parasitic diode p9 has the n-type well 302 as a cathode and the p-type well 304 as an anode. Furthermore, a parasitic diode p10 is associated between the n-type well 302 and the p-type substrate 301. The parasitic diode p10 has the n-type well 302 as a cathode and the p-type substrate 301 as an anode.

[0103] When an NMOSFET 300 is used as the transistor N2 of the internal switch SW1, the parasitic diode p8 in this figure corresponds to the previously mentioned body diode BD2.

[0104] 7, we will continue to explain the internal configuration of the timing control circuit 22. The timing control circuit 22 includes AND gates 220 and 221, a NAND gate 222, and delay stages 223 to 229. Note that the delay stages 223 to 229 may be, for example, a single inverter or an inverter stage in which a plurality of inverters are connected in cascade.

[0105] The AND gate 220 generates a logical AND signal A0 of the inverted lower gate drive signal XLG_LVS (= a signal obtained by logically inverting and level-shifting the lower gate drive signal LG) and the upper gate control signal HS, and outputs this as the internal input signal HGIN. Therefore, the internal input signal HGIN becomes high level when both the inverted lower gate drive signal XLG_LVS and the upper gate control signal HS are at high level, and becomes low level when at least one of the inverted lower gate drive signal XLG_LVS and the upper gate control signal HS is at low level.

[0106] The inverted lower gate drive signal XLG_LVS is input so that the timing control circuit 22 can recognize that the lower transistor 10L has been turned off. More specifically, by turning on the upper transistor 10H after the inverted lower gate drive signal XLG_LVS rises to a high level, it is possible to prevent the upper transistor 10H and the lower transistor 10L from being turned on simultaneously and suppress an excessive through current.

[0107] The AND gate 221 generates a logical AND signal A1 between the node signal n11 (=the logical inversion signal of the node signal n2a) and the upper gate control signal HS, and outputs this as the switch control signal S12. Therefore, the switch control signal S12 is at a high level when both the node signal n11 and the upper gate control signal HS are at a high level, and is at a low level when at least one of the node signal n11 and the upper gate control signal HS is at a low level.

[0108] The NAND gate 222 generates a NAND signal A2 of the node signal ndelay (=a signal obtained by delaying and logically inverting the node signal n11) and the upper gate control signal HS. Therefore, the NAND signal A2 is at a low level when both the node signal ndelay and the upper gate control signal HS are at a high level, and is at a high level when at least one of the node signal ndelay and the upper gate control signal HS is at a low level.

[0109] Delay stage 223 generates node signal n2a by providing an appropriate delay to internal input signal HGIN.

[0110] The delay stage 224 generates the node signal n11 by providing an appropriate delay to the node signal n2a and then inverting its logical level. If there is no need to provide a delay to the node signal n2a, a single inverter may be used as the delay stage 224.

[0111] The delay stage 225 generates the node signal ndelay by giving an appropriate delay to the node signal n11 and then inverting its logic level.

[0112] The delay stage 226 generates the switch control signal S11 by providing an appropriate delay to the node signal n2a.

[0113] The delay stage 227 generates the switch control signal S2 by giving an appropriate delay to the internal input signal HGIN and then inverting its logic level.

[0114] The delay stage 228 generates the switch control signal S3 by providing an appropriate delay to the NAND signal A2.

[0115] The delay stage 229 generates the switch control signal S4 by providing an appropriate delay to the switch control signal S3.

[0116] Figure 9 is a diagram showing an example of the operation of the timing control circuit 22, and depicts, from top to bottom, the upper gate control signal HS, the inverted lower gate drive signal XLG_LVS, the internal input signal HGIN, the switch control signals S1 to S4, the on / off states of the internal switches SW1 to SW3, and the capacitance value C21 of the capacitor circuit 21.

[0117] Before time t11, the upper gate control signal HS is at a low level, so the internal input signal HGIN is also at a low level. At this time, the switch control signals S11 and S12 are both at a low level, so the transistors N1 and N2 are both turned off. That is, the internal switch SW1 is turned off. Meanwhile, the switch control signals S2 and S3 are both at a high level, so the internal switch SW2 is turned on and the internal switch S3 is turned off. Therefore, the upper gate drive signal HG is pulled down to a low level, so the upper transistor 10H is fully turned off. Also, since the switch control signal S4 is at a high level, the capacitance value C21 of the capacitor circuit 21 is C21=C1+C2 (parallel combined value).

[0118] At time t11, the upper gate control signal HS rises to a high level. At this time, the node signal n11 (not shown) is at a high level, so the logical AND signal A1 (not shown) rises to a high level, and the switch control signal S12 rises to a high level. Meanwhile, at this time, the inverted lower gate drive signal XLG_LVS is at a low level, so the internal input signal HGIN is also at a low level, and the switch control signal S11 is maintained at a low level. As a result, the transistor N2 is turned on while the transistor N1 is turned off.

[0119] In this way, the timing control circuit 22 turns on the transistor N2 (NMOSFET) before turning on the transistor N1 (NDMOSFET). That is, the internal switch SW1 as a whole is kept in the off state, and only the transistor N2 is turned on. This timing control makes it possible to turn on the transistor N2, which is slower than the transistor N1, earlier and reduce its on-resistance in advance.

[0120] At time t12, when the inverted lower gate drive signal XLG_LVS rises to a high level, the internal input signal HGIN rises to a high level. However, at this point in time, the logic levels of the switch control signals S1 to S4 do not change, so the on / off states of the internal switches SW1 to SW3 and the capacitance value C21 of the capacitor circuit 21 remain unchanged.

[0121] At time t13, when the switch control signal S2, which is generated by delaying and logically inverting the internal input signal HGIN, falls to a low level, the internal switch SW2 is turned off. Therefore, all of the internal switches SW1 to SW3 are turned off, and the application terminal of the upper gate drive signal HG temporarily goes into a high impedance state.

[0122] At time t14, when the switch control signal S11, which is a delayed version of the internal input signal HGIN, rises to a high level, the transistor N1 is turned on. At this point, both the transistors N1 and N2 are in the on state, so the internal switch SW1 is turned on and precharging of the input gate capacitance Ciss by the input voltage Vi begins.

[0123] At time t15, when the node signal n11 (not shown), which is the delayed and logically inverted version of the internal input signal HGIN, falls to the low level, the logical product signal A1 (not shown) falls to the low level, and the switch control signal S12 falls to the low level. As a result, the transistor N2 is turned off. Meanwhile, at this point in time, the node signal ndelay (not shown) is at the low level, so the NAND signal A2 (not shown) is at the high level and the switch control signal S3 is maintained at the high level. In other words, the internal switch SW3 is off.

[0124] In this way, the timing control circuit 22 turns off the transistor N2 (and therefore the internal switch SW1) before turning on the internal switch SW3 to start charging with the boot voltage Vb. This timing control makes it possible to reliably cut off the sub-leakage current of the transistor N1 when a reverse bias is applied.

[0125] Even if transistor N2 is turned off at the above timing, the body diode BD2 remains forward biased until the potential difference between the input voltage Vi and the upper gate drive signal HG falls below the forward drop voltage Vf of the body diode BD2, and therefore the precharging of the input gate capacitance Ciss by the input voltage Vi continues.

[0126] In addition, since the transistor N2 is an NMOSFET rather than an NDMOSFET, no sub-leakage current flows to the p-type substrate even if a current flows through the body diode BD2.

[0127] At time t16, following the high-level transition of the node signal ndelay (not shown) and the low-level transition of the NAND signal A2 (not shown), the switch signal S3 obtained by delaying the NAND signal A2 falls to a low level. As a result, the internal switch SW3 turns on, and charging of the input gate capacitance Ciss by the boot voltage Vb begins.

[0128] At time t17, the switch control signal S4, which is a delayed version of the switch control signal S3, falls to a low level. At this time, the capacitance C21 of the capacitor circuit 21 is reduced to C21=(C1·C2) / (C1+C2) (series combined value). As a result, it is possible to suppress the reduction in the boot voltage Vb that accompanies the charging of the input gate capacitance Ciss.

[0129] At time t18, when the high-side gate control signal HS falls to a low level, the internal input signal HGIN falls to a low level. However, at this point in time, there is no change in the logical levels of the switch control signals S1 to S4, so the on / off states of the internal switches SW1 to SW3 and the capacitance value C21 of the capacitor circuit 21 remain unchanged.

[0130] At time t19, following the high-level transition of the NAND signal A2 (not shown), the switch signal S3, which is the delayed NAND signal A2, rises to a high level, turning off the internal switch SW3. Therefore, all of the internal switches SW1 to SW3 are turned off, and the application terminal of the upper gate drive signal HG temporarily goes into a high impedance state.

[0131] At time t20, when the switch control signal S2, which is a delayed and logically inverted version of the internal input signal HGIN, rises to a high level, the internal switch SW2 is turned on, and the high-side gate drive signal HG is pulled to a low level, so that the high-side transistor 10H is fully off.

[0132] At time t21, the switch control signal S4, which is a delayed version of the switch control signal S3, rises to a high level. As a result, the capacitance C21 of the capacitor circuit 21 is increased to C21=C1+C2 (parallel combined value). In addition, the switch control signal S11, which is a delayed version of the internal input signal HGIN, falls to a low level, turning off the transistor N1.

[0133] <Other Modifications> In addition to the above-mentioned embodiments, the various technical features disclosed in this specification can be modified in various ways without departing from the spirit of the technical creation. For example, the gate driver disclosed in this specification may drive an IGBT. Thus, the above-mentioned embodiments should be considered as illustrative and not restrictive in all respects, and the technical scope of the present invention should not be limited to the above-mentioned embodiments, but should be understood to include all modifications that fall within the meaning and scope equivalent to the claims. [Industrial Applicability]

[0134] The gate drivers disclosed herein may be used, for example, as a means for driving the upper transistors (eg, NMOSFETs) of a half-bridge output stage. [Explanation of symbols]

[0135] 1 Switching power supply 10H Upper transistor (NMOSFET) 10L Lower transistor (NMOSFET) 20H Upper driver 20L Lower Driver 21 Capacitor Circuit 22 Timing control circuit 220, 221 AND gate 222 NAND Gate 223~229 Delay stage 30H Upper level shifter 30L Lower Level Shifter 40 Logic Circuits 100 Semiconductor device (power supply control IC) 300 NMOSFET 301 p type substrate 302 n-type well 303 n+ type semiconductor region (contact) 304 p-type well 305 n+ type semiconductor region (drain) 306 n+ type semiconductor region (source) 307 p+ type semiconductor region (contact) 308, 309 n-type semiconductor region 310 Gate oxide 311 Gate electrode BD1, BD2 body diodes C, C1, C2 capacitors Cb Boot capacitor DLY Delay stage L Inductor N1 NDMOSFET N2 NMOSFET p1~p7 Parasitic capacitors p8~p10 Parasitic diode SW0~SW6 Internal switches

Claims

1. A gate driver for driving an upper N-channel transistor in a half-bridge circuit including an upper N-channel transistor connected between an input voltage application terminal and a switch voltage application terminal, and a lower rectifier element connected between the switch voltage application terminal and a ground terminal, the gate driver comprising: a capacitor circuit connected between an application end of a boot voltage, the boot voltage being higher than the switch voltage by a voltage across a boot capacitor, and an application end of the switch voltage; a timing control circuit that precharges an input gate capacitance of the transistor with the input voltage when the transistor is turned on, and then charges the input gate capacitance with the boot voltage, and reduces a capacitance value of the capacitor circuit after the transistor is turned on; having A gate driver that raises the boot voltage by lowering a capacitance value of the capacitor circuit.

2. a first internal switch connected between an application terminal of the input voltage and a gate of the transistor, a second internal switch connected between a gate of the transistor and an application terminal of the switch voltage, and a third internal switch connected between an application terminal of the boot voltage and a gate of the transistor, The gate driver according to claim 1 , wherein the timing control circuit controls switching timings of the first internal switch, the second internal switch, and the third internal switch.

3. the capacitor circuit includes a first capacitor having a first end connected to the application end of the boot voltage, a second capacitor having a first end connected to the application end of the switch voltage, a fourth internal switch connected between the second end of the first capacitor and the application end of the switch voltage, a fifth internal switch connected between the second end of the first capacitor and the second end of the second capacitor, and a sixth internal switch connected between the application end of the boot voltage and the second end of the second capacitor, The gate driver according to claim 2 , wherein the timing control circuit controls switching timings of the fourth internal switch, the fifth internal switch, and the sixth internal switch.

4. The timing control circuit includes: a first driving phase in which the first internal switch, the third internal switch, and the fifth internal switch are turned off and the second internal switch, the fourth internal switch, and the sixth internal switch are turned on; a second driving phase in which the second internal switch, the third internal switch, and the fifth internal switch are turned off and the first internal switch, the fourth internal switch, and the sixth internal switch are turned on; a third driving phase in which the first internal switch, the second internal switch, and the fifth internal switch are turned off and the third internal switch, the fourth internal switch, and the sixth internal switch are turned on; a fourth driving phase in which the first internal switch, the second internal switch, the fourth internal switch, and the sixth internal switch are turned off and the third internal switch and the fifth internal switch are turned on; The gate driver according to claim 3 , wherein the gate driver sequentially switches between

5. The first internal switch is an NDMOSFET having a drain connected to an application terminal of the input voltage; an NMOSFET having a source connected to the source of said NDMOSFET and a drain connected to the gate of said transistor; The gate driver according to any one of claims 2 to 4, comprising:

6. The gate driver of claim 5 , wherein the timing control circuit turns on the NMOSFET before turning on the NDMOSFET and turns off the NMOSFET before turning on the third internal switch.

7. The gate driver according to claim 2 , wherein the third internal switch is a PDMOSFET.

8. A semiconductor device comprising the gate driver according to any one of claims 1 to 7 integrated therein.

9. 9. The semiconductor device according to claim 8, further comprising a boot capacitor connected between the application end of said boot voltage and the application end of said switch voltage, said boot capacitor being integrated.

10. 10. The semiconductor device according to claim 8, further comprising an upper N-channel transistor connected between the input voltage application terminal and the switch voltage application terminal, the upper N-channel transistor being integrated.

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