Switch circuit

Abstract

To provide a switch circuit capable of overcurrent protection in a wide output voltage range.SOLUTION: The main transistor 102 is provided between an input terminal VIN and an output terminal VOUT. The replica transistor 104 has the same configuration as the main transistor 102. The output-voltage monitoring circuit 120 compares the output-voltage VOUT with a threshold voltage VTH1 and generates a voltage detection signal VOUTDET. The second current detection circuit 140 includes a first switch SW1 and a first resistor R1 connected between the source of the replica transistor 104 and the ground. The current limiting circuit 150 limits the current based on one of the current detection signals VCS1 and VCS2 that corresponds to the voltage detection signal VOUTDET.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a switch circuit. [Background technology]

[0002] A switch circuit is used to switch between conducting and blocking voltage. The switch circuit includes a main transistor provided between an input terminal and an output terminal. To prevent an overcurrent from flowing through this main transistor, the switch circuit is provided with an overcurrent protection circuit.

[0003] There are two main methods for detecting current in overcurrent protection circuits. One is to insert a sense resistor in series with the main transistor and use the voltage drop across the sense resistor as the current detection signal. This method has the problem of power consumption in the sense resistor.

[0004] The other method is to place a replica transistor in parallel with the main transistor, which operates in the same state as the main transistor, and detect the current flowing through the replica transistor. This method solves the power consumption problem by making the replica transistor significantly smaller than the main transistor. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-110521

[0006] [overview] The present disclosure has been made in light of such a situation, and it is an exemplary purpose of an embodiment thereof to provide a switch circuit capable of overcurrent protection over a wide range of output voltages.

[0007] A switch circuit according to an embodiment of the present disclosure includes an input terminal and an output terminal, an N-type main transistor connected between the input terminal and the output terminal, a replica transistor having the same configuration as the main transistor, with its drain connected to the input terminal, its gate connected to the gate of the main transistor, and its source connected to ground via a current limiting resistor, an output voltage monitoring circuit that compares an output voltage generated at the output terminal with a predetermined threshold voltage and generates a voltage detection signal that takes a first level when the output voltage is higher than the threshold voltage and a second level when the output voltage is lower than the threshold voltage, a first transistor connected to the source of the replica transistor, and a first transistor that controls the first transistor so that the source voltage of the replica transistor approaches the source voltage of the main transistor. a first current detection circuit including a first amplifier controlling the replica transistor and generating a first current detection signal proportional to the current flowing through the first transistor; a second current detection circuit including a first resistor and a first switch connected in series between the source of the replica transistor and ground, the first switch being off when the voltage detection signal is at a first level and on when the voltage detection signal is at a second level, and generating a second current detection signal proportional to the current flowing through the first resistor; and a current limiting circuit that adjusts the gate voltage of the main transistor in accordance with the first current detection signal when the voltage detection signal is at the first level, and adjusts the gate voltage of the main transistor in accordance with the second current detection signal when the voltage detection signal is at the second level.

[0008] Any combination of the above elements, or mutual substitution of elements or expressions between methods, devices, systems, etc., are also valid aspects of the present invention or the present disclosure. Furthermore, the description in this section (Means for Solving the Problems) does not explain all essential features of the present invention, and therefore, subcombinations of the described features may also constitute the present invention. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a circuit diagram of a system including a switch circuit according to a comparative technique. [Figure 2] FIG. 2 is a circuit diagram of a switch circuit according to an embodiment. [Figure 3] FIG. 3 is a circuit diagram of the switch circuit when VOUT > VTH1. [Figure 4] FIG. 4 is a circuit diagram of the switch circuit when VOUT < VTH1. [Figure 5] FIG. 5 is a diagram showing the relationship between the output voltage VOUT and the limit value of the output current IOUT. [Figure 6] FIG. 6 is a circuit diagram of a switch circuit 100A according to a modification. [Figure 7] FIG. 7 is a circuit diagram showing a configuration example of a level shifter and a first amplifier.

[0010] [Detailed Description] (Overview of the Embodiment) The overview of some exemplary embodiments of the present disclosure will be described. This overview is for the purpose of providing a basic understanding of the embodiments as a prelude to the detailed description to follow, and simplifies and describes some concepts of one or more embodiments. It does not limit the scope of the invention or disclosure. This overview is not an all-inclusive overview of all possible embodiments, and is not intended to identify important elements of all embodiments or to delineate the scope of some or all aspects. For convenience, "one embodiment" may be used to refer to one embodiment (example or modification) or multiple embodiments (examples or modifications) disclosed herein.

[0011] A switch circuit according to one embodiment includes an input terminal and an output terminal, an N-type main transistor connected between the input terminal and the output terminal, a replica transistor having the same configuration as the main transistor, with its drain connected to the input terminal, its gate connected to the gate of the main transistor, and its source connected to ground via a current limiting resistor, an output voltage monitoring circuit that compares an output voltage generated at the output terminal with a predetermined threshold voltage and generates a voltage detection signal that takes a first level when the output voltage is higher than the threshold voltage and a second level when the output voltage is lower than the threshold voltage, a first transistor connected to the source of the replica transistor, and a first transistor that controls the first transistor so that the source voltage of the replica transistor approaches the source voltage of the main transistor. a first current detection circuit including a first amplifier controlling the replica transistor and generating a first current detection signal proportional to the current flowing through the first transistor; a second current detection circuit including a first resistor and a first switch connected in series between the source of the replica transistor and ground, the first switch being off when the voltage detection signal is at a first level and on when the voltage detection signal is at a second level, and generating a second current detection signal proportional to the current flowing through the first resistor; and a current limiting circuit that adjusts the gate voltage of the main transistor in accordance with the first current detection signal when the voltage detection signal is at the first level, and adjusts the gate voltage of the main transistor in accordance with the second current detection signal when the voltage detection signal is at the second level.

[0012] When the output voltage, i.e., the source voltage of the main transistor, is low, the operating point of the first amplifier cannot be secured, which may result in a decrease in the accuracy of overcurrent protection or ineffectiveness of overcurrent protection. With the above configuration, when the output voltage is higher than the threshold voltage, overcurrent protection is performed based on the first current detection signal generated by the first current detection circuit. When the output voltage falls below the threshold voltage, the first current detection circuit is disabled, and overcurrent protection is performed based on the second current detection signal generated by the second current detection circuit. This enables accurate overcurrent protection over a wide output voltage range.

[0013] In one embodiment, the current limiting circuit may feedback control the gate voltage of the main transistor so that the first current detection signal does not exceed the reference voltage when the voltage detection signal is at a first level, and may feedback control the gate voltage of the main transistor so that the second current detection signal does not exceed the reference voltage when the voltage detection signal is at a second level.

[0014] In one embodiment, the current limiting circuit may include a second transistor connected between the gate of the main transistor and ground, and a second amplifier having an output connected to the gate of the second transistor and having one input terminal to which a first current detection signal is input when the voltage detection signal is at a first level and a second current detection signal is input when the voltage detection signal is at a second level.

[0015] In one embodiment, the switch circuit may further include a first protection circuit including a third resistor connected in series with the first transistor and a third amplifier configured to amplify a voltage drop across the third resistor and generate a third current detection signal, and configured to turn off the main transistor when the third current detection signal exceeds a first threshold voltage while the voltage detection signal is at a first level.

[0016] If the current limiting resistor shorts out, the correlation between the first current detection signal and the output current disappears, and the current limiting circuit no longer limits the current. When the current limiting resistor shorts out, a large current flows through the third resistor. The first protection circuit can detect a short in the current limiting resistor, and if a short is detected, it can protect the circuit by turning off the main transistor.

[0017] In one embodiment, when the voltage detection signal is at the second level, the first protection circuit may compare a fourth current detection signal corresponding to the voltage drop across the first resistor with a second threshold voltage, and turn off the main transistor when the fourth current detection signal exceeds the second threshold voltage.

[0018] In one embodiment, the fourth current detection signal may be the same signal as the second current detection signal.

[0019] In one embodiment, the first threshold voltage may be a constant voltage and the second threshold voltage may be dependent on the output voltage.

[0020] In one embodiment, the switch circuit may further include a second protection circuit that turns off the main transistor when the difference between the source voltage and the output voltage of the replica transistor exceeds a predetermined threshold voltage. This allows a ground fault at the output terminal to be detected and the circuit to be protected when the voltage detection signal is at a first level. Furthermore, when the voltage detection signal is at a second level, the circuit can be protected in a region where the output voltage is very low.

[0021] In one embodiment, the first current detection circuit may further include a level shifter that shifts the source voltage and output voltage of the replica transistor. The level shifter may be capable of independently adjusting the shift amounts of the source voltage and output voltage. This allows for canceling variations in the gate threshold voltages of the main transistor and the replica transistor.

[0022] In one embodiment, the first amplifier may have an adjustable input offset voltage, which can reduce the error between the drain-source voltage of the replica transistor and the drain-source voltage of the main transistor.

[0023] In one embodiment, the switch circuit may be monolithically integrated on a single semiconductor substrate. "Monolithic integration" includes cases where all of the circuit components are formed on a semiconductor substrate, or where the main circuit components are monolithically integrated, and some resistors, capacitors, etc., for adjusting circuit constants may be provided outside the semiconductor substrate. By integrating the circuit on a single chip, the circuit area can be reduced and the characteristics of the circuit elements can be maintained uniform.

[0024] (Embodiment) Preferred embodiments will be described below with reference to the drawings. The same or equivalent components, parts, and processes shown in each drawing will be given the same reference numerals, and redundant explanations will be omitted as appropriate. Furthermore, the embodiments are examples and do not limit the disclosure and invention, and all features and combinations thereof described in the embodiments are not necessarily essential to the disclosure and invention.

[0025] In this specification, "a state in which component A is connected to component B" includes not only a case in which component A and component B are directly physically connected to each other, but also a case in which component A and component B are indirectly connected to each other via other components that do not substantially affect the electrical connection between them or that do not impair the function or effect achieved by their connection.

[0026] Similarly, "a state in which component C is connected (provided) between component A and component B" includes not only a case in which component A and component C, or component B and component C, are directly connected, but also a case in which they are indirectly connected via other components that do not substantially affect the electrical connection state between them or that do not impair the function or effect achieved by their combination.

[0027] Before describing the switch circuit according to the embodiment, a problem that occurs in current detection using replica transistors will be described with reference to a comparative technique.

[0028] (Comparative Technology) 1 is a circuit diagram of a system 2R including a switch circuit 100R according to a comparative example. The system 2R includes a power supply circuit 4, a switch circuit 100R, and a load circuit 6.

[0029] The switch circuit 100R receives an input voltage VIN from a power supply circuit 4 and supplies an output voltage VOUT to a load 6 connected to an output terminal VOUT. In this specification, the symbols and names attached to terminals (pins) indicate the voltages generated at those terminals (pins).

[0030] The switch circuit 100R includes a main transistor 102, a replica transistor 104, a switch control section 110R, a current detection circuit 130R, and a current limiting circuit 150R.

[0031] The main transistor 102 is an N-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor), with its drain connected to an input terminal VIN and its source connected to an output terminal OUT. The switch control unit 110R controls the on / off of the main transistor 102 in response to a control signal SWCTRL. For example, the switch control unit 110R includes a charge pump circuit 112 and a gate driver 114. The charge pump circuit 112 controls a gate high voltage V to be applied to the gate of the main transistor 102. GH The gate driver 114 supplies a gate high voltage VGH to the gate of the main transistor 102 when the control signal SWCTRL instructs the main transistor 102 to be turned on.

[0032] The replica transistor 104 is an N-channel MOSFET of the same type as the main transistor 102. The drain of the replica transistor 104 is connected to the input terminal VIN, and the gate is connected to the gate of the main transistor 102.

[0033] The current detection circuit 130R includes a first transistor M1, a first amplifier AMP1, and an external current limiting resistor RILIM. The current limiting resistor RILIM is a chip component connected to a current limiting terminal ILIM.

[0034] The first transistor M1 is provided between the source of the replica transistor 104 and the current limiting terminal ILIM. The first amplifier AMP1 feedback-controls the gate voltage of the first transistor M1 so that the source voltage VS of the replica transistor 104 approaches the source voltage of the main transistor 102 (i.e., the output voltage VOUT).

[0035] The main transistor 102 and replica transistor 104 have the same source voltages, gate voltages, and drain voltages, so a detection current ICS=IOUT×α flows through the replica transistor 104, which is proportional to the output current IOUT flowing through the main transistor 102. When the size ratio between the main transistor 102 and replica transistor 104 is N:1, the coefficient α is 1 / N.

[0036] When the detection current ICS flows through the current limiting resistor RILIM, a current detection signal VCS is generated at the current limiting terminal ILIM. VCS=ICS×RILIM =IOUT×α×RILIM

[0037] The current limiting circuit 150R adjusts the gate voltage of the main transistor 102 so that the current detection signal VCS does not exceed the reference voltage VREF_LIM. The current limiting circuit 150R includes, for example, a second transistor M2, a second resistor R2, and a second amplifier AMP2.

[0038] When the current limiter circuit 150R is in the current limit state, VCS=VREF_LIM At this time, the output current IOUT is IOCL=VREF_LIM×N / RILIM In other words, the output current IOUT is clamped to the overcurrent threshold IOCL, which is determined according to the resistance value of the external current limiting resistor RILIM, and overcurrent protection is activated.

[0039] The above is the configuration of the switch circuit 100R according to the comparative technology. As a result of examining the switch circuit 100R according to the comparative technology, the present inventor has come to recognize several problems. Note that these problems should not be considered as common knowledge among those skilled in the art.

[0040] Assignment 1 Suppose that the output terminal VOUT is shorted to ground (grounded) while the current limiting circuit 150R is providing overcurrent protection. Due to a response delay in the first amplifier AMP1, there is a delay before the source voltage VS of the replica transistor 104 becomes equal to the output voltage VOUT. In other words, the drain-source voltage of the main transistor 102 and the drain-source voltage of the replica transistor 104 are no longer equal, and ICS becomes smaller than IOUT × α. As a result, the effective overcurrent threshold IOCL increases, causing an overcurrent to flow through the main transistor 102. Furthermore, due to a response delay in the second amplifier AMP2, there is a delay before the gate voltage of the main transistor 102 drops. As such, overcurrent protection becomes inaccurate when the output voltage VOUT drops.

[0041] Assignment 2 If the current limiting terminal ILIM is grounded, that is, if the resistance limiting resistor RILIM is shorted, the current detection signal VCS becomes small and the current limiting circuit 150R no longer provides protection.

[0042] Task 3 When the switch circuit 100R starts up, that is, immediately after the main transistor 102 turns on, the output voltage VOUT may be low. At this time, the operating point of the first amplifier AMP1 cannot be secured, the source voltages VOUT and VS of the main transistor 102 and replica transistor 104 differ, and the current ICS flowing through the replica transistor 104 becomes smaller than α×IOUT, resulting in inaccurate overcurrent protection.

[0043] The switch circuit 100 according to the embodiment solves at least one of the above problems 1 to 3.

[0044] (Embodiment) 2 is a circuit diagram of a switch circuit 100 according to an embodiment. The switch circuit 100 is used in a system 2. The switch circuit 100 includes a main transistor 102, a replica transistor 104, a switch control unit 110, an output voltage monitoring circuit 120, a first current detection circuit 130, a second current detection circuit 140, a current limiting circuit 150, a first protection circuit 160, and a second protection circuit 170, which are integrated on a single semiconductor substrate.

[0045] The main transistor 102 is an N-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor), with its drain connected to an input terminal VIN and its source connected to an output terminal OUT. The input terminal VIN receives an input voltage VIN from a power supply circuit 4. A smoothing capacitor C1 and a load circuit 6 are connected to the output terminal VOUT.

[0046] The switch control unit 110 controls the on / off of the main transistor 102 in response to a control signal SWCTRL. The switch control unit 110 includes a charge pump circuit 112 and a gate driver 114, for example.

[0047] The replica transistor 104 is an N-channel MOSFET of the same type as the main transistor 102. The drain of the replica transistor 104 is connected to the input terminal VIN, and the gate is connected to the gate of the main transistor 102.

[0048] The first current detection circuit 130 includes a first transistor M1, a first amplifier AMP1, and an external current limiting resistor RILIM. The current limiting resistor RILIM is a chip component connected to a current limiting terminal ILIM.

[0049] The output voltage monitoring circuit 120 compares the output voltage VOUT generated at the output terminal VOUT with a predetermined threshold voltage VTH1, and generates a voltage detection signal VOUDET that takes a first level (e.g., high, 1) when the output voltage VOUT is higher than the threshold voltage VTH1, and a second level (e.g., low, 0) when the output voltage VOUT is lower than the threshold voltage VTH1. The threshold voltage VTH1 can be set lower than the lower limit of the voltage range that the output voltage VOUT can take in a normal state, and may be, for example, approximately several hundred mV to 1 V. For example, the output voltage monitoring circuit 120 may include a voltage comparator 122.

[0050] The first transistor M1 is provided between the source of the replica transistor 104 and the current limiting terminal ILIM.

[0051] The first amplifier AMP1 becomes active when the voltage detection signal VOUTDET is at a first level (1), and feedback controls the gate voltage of the first transistor M1 so that the source voltage VS of the replica transistor 104 approaches the source voltage of the main transistor 102 (i.e., the output voltage VOUT).

[0052] The main transistor 102 and replica transistor 104 have the same source voltages, gate voltages, and drain voltages, so a detection current ICS=IOUT×α flows through the replica transistor 104, which is proportional to the output current IOUT flowing through the main transistor 102. α is a coefficient determined by the size ratio (N:1) between the main transistor 102 and the replica transistor 104.

[0053] When the detection current ICS flows through the current limiting resistor RILIM, a first current detection signal VCS1 is generated at the current limiting terminal ILIM. VCS1=ICS×RILIM =IOUT×α×RILIM

[0054] The first amplifier AMP1 turns off the first transistor M1 when the voltage detection signal VOUTDET is at the second level (0). At this time, no current flows through the current limiting resistor RILIM, so VCS1=0V.

[0055] The second current detection circuit 140 includes a first resistor R1 and a first switch SW1 connected in series between the source of the replica transistor 104 and ground. The first switch SW1 is off when the voltage detection signal VOUTDET is at a first level (1), and is on when the voltage detection signal VOUTDET is at a second level (0). The second current detection circuit 140 may further include a fourth resistor R4 inserted between the source of the replica transistor 104 and the first switch SW1.

[0056] A detection signal ICS proportional to the output current IOUT flowing through the main transistor 102 flows through the replica transistor 104 . ICS=IOUT×β

[0057] When the voltage detection signal VOUTDET is at the second level (0), the first transistor M1 is off and the first switch SW1 is on, so the current ICS flowing through the replica transistor 104 flows through the first resistor R1. The second current detection circuit 140 generates a second current detection signal VCS2 proportional to the current ICS flowing through the first resistor R1. The second current detection signal VCS2 may be a voltage drop across the first resistor R1. VCS2=ICS×R1 =IOUT×β×R1

[0058] When VOUTDET is at the second level (0), the amplifier AMP1 is not operating, and the drain-source voltage of the main transistor 102 and the drain-source voltage of the replica transistor 104 are not equal. Therefore, the coefficient β is a value that deviates from α. In other words, the accuracy of current detection by the second current detection circuit 140 is lower than the accuracy of current detection by the first current detection circuit 130. In exchange for this, the second current detection circuit 140 is faster than the first current detection circuit 130 because it does not have an amplifier with a response delay.

[0059] A first current detection signal VCS1 and a second current detection signal VCS2 are input to the current limiting circuit 150. When the voltage detection signal VOUTDET is at a first level (1), the current limiting circuit 150 adjusts the gate voltage of the main transistor 102 in response to the first current detection signal VCS1. When the voltage detection signal VOUTDET is at a second level (0), the current limiting circuit 150 adjusts the gate voltage of the main transistor 102 in response to the second current detection signal VCS2.

[0060] The current limiting circuit 150 includes a selector SEL1, a second amplifier AMP2, a second transistor M2, a second resistor R2, and a control unit 152.

[0061] The second transistor M2 and the second resistor R2 are connected in series between the gate of the main transistor 102 and ground. The selector SEL1 receives the first current detection signal VCS1 and the second current detection signal VCS2, and selects the first current detection signal VCS1 when the voltage detection signal VOUTDET is at a first level (1), and selects the second current detection signal VCS2 when the voltage detection signal VOUTDET is at a second level (0). The second amplifier AMP2 controls the gate voltage of the second transistor M2 so that the first current detection signal VCS1 selected by the selector SEL1 does not exceed the reference voltage VREF_LIM when the voltage detection signal VOUTDET is at the first level (1). Furthermore, the second amplifier AMP2 controls the gate voltage of the second transistor M2 so that the second current detection signal VCS2 selected by the selector SEL1 does not exceed the reference voltage VREF_LIM when the voltage detection signal VOUTDET is at the second level (0).

[0062] The first protection circuit 160 includes a third resistor R3 and a third amplifier AMP3. The third resistor R3 is connected in series with the first transistor M1. The third amplifier AMP3 amplifies the voltage drop across the third resistor R3 and generates a third current detection signal VCS3.

[0063] When the voltage detection signal VOUTDET is at the first level (1), the first protection circuit 160 compares the third current detection signal VCS3 with the first threshold voltage VTH3, and turns off the main transistor 102 when the third current detection signal VCS3 exceeds the first threshold voltage VTH3.

[0064] When the voltage detection signal VOUTDET is at the second level (0), the first protection circuit 160 compares the fourth current detection signal VCS4, which corresponds to the voltage drop across the first resistor R1, with the second threshold voltage VTH4, and turns off the main transistor 102 when the fourth current detection signal VCS4 exceeds the second threshold voltage VTH4.

[0065] In this embodiment, the fourth current detection signal VCS4 is the same signal as the second current detection signal VCS2. VCS4=ICS×R1 =IOUT×β×R1

[0066] The first threshold voltage VTH3 is a constant voltage, and the second threshold voltage VTH4 is a voltage that corresponds to the output voltage VOUT. For example, the first threshold voltage VTH3 is 0.2 V, and the second threshold voltage VTH4 is a voltage obtained by adding an offset voltage V (for example, 0.05 V) to the output voltage VOUT.

[0067] For example, the first protection circuit 160 includes selectors SEL2 and SEL3 and a comparator 162. The selector SEL2 receives the third current detection signal VCS3 and the fourth current detection signal VCS, and selects one of them according to the voltage detection signal VOUTDET. The selector SEL3 receives the first threshold voltage VTH3 and the second threshold voltage VTH3, and selects one of them according to the voltage detection signal VOUTDET.

[0068] The comparator 162 compares the output voltage of the selector SEL2 with the output voltage of the selector SEL3, and asserts an overcurrent detection signal ILIMDET when the output voltage of the selector SEL2 exceeds the output voltage of the selector SEL3.

[0069] The switch control unit 110 turns off the main transistor 102 in response to the assertion of the overcurrent detection signal ILIMDET. For example, the charge pump circuit 112 of the switch control unit 110 can be switched between enabled and disabled according to the overcurrent detection signal ILIMDET, and is in the disabled state while the overcurrent detection signal ILIMDET is asserted.

[0070] In addition, the gate driver 114 may be configured such that the voltage between the gate and source of the main transistor 102 becomes 0V according to the overcurrent detection signal ILIMDET.

[0071] The second protection circuit 170 compares the difference between the source voltage VS of the replica transistor 104 and the output voltage VOUT with a predetermined threshold voltage VTH5. When the difference between the source voltage VS and the output voltage VOUT exceeds the threshold voltage VTH5, the second protection circuit 170 turns off the main transistor 102. The threshold voltage VTH5 is, for example, 0.05V.

[0072] For example, the second protection circuit 170 includes a comparator 172. The comparator 172 compares the source voltage VS of the replica transistor 104 with the voltage obtained by adding the fifth threshold voltage VTH5 to the output voltage VOUT, and when VS > VOUT + VTH5, asserts the overcurrent detection signal CRITCURDET.

[0073] When VOUT > VTH1, the source voltage VS of the replica transistor 104 is stabilized at a voltage equal to the output voltage VOUT by the first current detection circuit 130. When the output terminal VOUT is grounded, the potential difference between the output voltage VOUT and the source voltage VS increases, and the overcurrent detection signal CRITCURDET is asserted.

[0074] When VOUT < VTH1, the source voltage VS of the replica transistor 104 is VS = ICS×(R1 + R4) This results in. When the current IOUT flowing through the main transistor 102 becomes an overcurrent, VS > VOUT + VTH5, and the overcurrent detection signal CRITCURDET is asserted.

[0075] In response to the assertion of the overcurrent detection signal CRITCURDET, the switch control unit 110 turns off the main transistor 102. For example, the charge pump circuit 112 of the switch control unit 110 can switch between enable and disable according to the overcurrent detection signal CRITCURDET, and is in the disable state while the overcurrent detection signal CRITCURDET is asserted.

[0076] The logic circuit 116 is a NOR gate, which outputs a low when at least one of the two overcurrent detection signals ILIMDET and CRITCURDET is asserted (1), and outputs a high when both of the two overcurrent detection signals ILIMDET and CRITCURDET are negated (0).

[0077] The above is the configuration of the switch circuit 100. Subsequently, its operation will be described for the cases when VOUT > VTH1 and when VOUT < VTH1 respectively.

[0078] · VOUT > VTH1 FIG. 3 is a circuit diagram of the switch circuit 100 when VOUT > VTH1.

[0079] The voltage detection signal VOUTDET, which is the output of the output voltage monitoring circuit 120, becomes the first level (1). As a result, the first amplifier AMP1 is turned on and the first current detection circuit 130 operates. On the other hand, since the first switch SW1 is turned off, the second current detection circuit 140 is turned off.

[0080] The current limit circuit 150 controls the gate voltage of the main transistor 102 so that the first current detection signal VCS1 generated by the first current detection circuit 130 does not exceed the reference voltage VREF_LIM.

[0081] Here, in the state where VOUT>VTH1, the drain-source voltages of the main transistor 102 and replica transistor 104 are equal, so the current limit amount of the output current IOUT is constant and does not depend on the output voltage VOUT, and accurate current limiting is performed.

[0082] If the current limiting resistor RILIM is shorted, that is, if the current limiting terminal ILIM is shorted to ground, the correlation between the first current detection signal VCS1 and the output current IOUT is lost, and the overcurrent protection provided by the current limiting circuit 150 becomes ineffective.

[0083] When the current limiting resistor RILIM is shorted, a large current flows through the first transistor M1 and the third resistor R3, causing a large voltage drop across the third resistor R3. As a result, the third current detection signal VCS3 becomes higher than the first threshold voltage VTH3, and the overcurrent detection signal ILIMDET is asserted. As a result, the main transistor 102 is turned off. In this way, the first protection circuit 160 can detect a shorted state of the current limiting resistor RILIM and protect the circuit by turning off the main transistor 102.

[0084] When the switch circuit 100 is operating normally, the output voltage VOUT and the source voltage VS of the replica transistor 104 are almost equal due to feedback from the first amplifier AMP1. However, if the output terminal OUT is shorted to ground, the potential difference between the output voltage VOUT and the source voltage VS increases. When the potential difference between the output voltage VOUT and the source voltage VS exceeds the threshold voltage VTH5, the second protection circuit 170 asserts a flag CRITCURDET indicating an abnormality and turns off the main transistor 102.

[0085] In this way, the second protection circuit 170 can detect a ground fault at the output terminal VOUT and protect the switch circuit 100.

[0086] VOUT <VTH1 Figure 4 is a circuit diagram of the switch circuit 100 when VOUT < VTH1. The voltage detection signal VOUTDET, which is the output of the output voltage monitoring circuit 120, becomes the second level (0). As a result, the first amplifier AMP1 of the first current detection circuit 130 turns off, and the first transistor M1 turns off. On the other hand, the first switch SW1 of the second current detection circuit 140 turns on.

[0087] The current ICS flowing through the replica transistor 104 flows into the second current detection circuit 140, and current detection signals VCS2 and VCS4 are generated.

[0088] The state of VOUT < VTH1 can be roughly divided into three regions. In order from the lowest output voltage VOUT, they are the first region RNG1, the second region RNG2, and the third region RNG3.

[0089] In the third region RNG3, current limiting by the current limiting circuit 150 is effective. The current limiting circuit 150 adjusts the gate voltage of the main transistor 102 so that the second bit detection signal VCS2 does not exceed the reference voltage VREF_LIM. As a result, current limiting is applied.

[0090] In the state of VOUT < VTH1, since the drain-source voltage between the main transistor 102 and the replica transistor 104 is not equal, the current limit amount of the output current IOUT changes depending on the output voltage VOUT.

[0091] In the second region RNG2, protection by the second protection circuit 170 becomes effective. In the state of VOUT < VTH1, since the first switch SW1 is on, the current ICS flowing through the replica transistor 104 flows into the second current detection circuit 140. As a result, the source voltage VS of the replica transistor 104 is VS = ICS × (R4 + R1) When the output current IOUT is in an overcurrent state, this source voltage VS exceeds VOUT + VTH5, the overcurrent detection signal CRITCUR is asserted, and the main transistor 102 turns off.

[0092] If ICS = IOUT × β, then the output current IOUT in the second region RNG2 is limited by the second protection circuit 170 so as not to exceed the limit current amount ICRIT. ICRIT = (VOUT + VTH5) / (β(R4 + R1))

[0093] The output voltage Vx at the boundary between the second region RNG2 and the third region RNG3 is approximately VREF_ILIM / R1 × (R1 + R2).

[0094] In the first region RNG1, the protection by the first protection circuit 160 becomes effective. Specifically, when the fourth current detection signal VCS4 exceeds the second threshold VTH4, the overcurrent detection signal ILIMDET is asserted and protection is applied. VCS4 = ICS × R1 Since VCS4 = ICS × R1 and ICS = IOUT × β, the limit amount ILIM of the output current IOUT in the first region RNG1 is ILIM = VTH4 / (β·R1) That is.

[0095] Figure 5 is a diagram showing the relationship between the output voltage VOUT and the limit amount of the output current IOUT. In the range where VOUT > VTH1, the first current detection circuit 130 and the current limit circuit 150 become effective, and the limit amount of the output current IOUT becomes constant regardless of the output voltage VOUT.

[0096] In the third region RNG3 where VOUT < VTH1, the current limit by the second current detection circuit 140 and the current limit circuit 150 is effective. In this region, since the coefficient β of the second current detection circuit 140 has a dependence on the output voltage VOUT, the limit amount of the output current IOUT has a negative dependence on the output voltage VOUT. [[ID=二十七]]

[0097] In the third region RNG3, when the second current detection signal VCS2 becomes higher to a certain voltage level, it enters the second region RNG2.

[0098] In the second region RNG2, the current limit by the second protection circuit 170 is effective.

[0099] In the first region RNG1, the protection provided by the first protection circuit 160 is effective.

[0100] The above is the operation of the switch circuit 100. This switch circuit 100 enables overcurrent protection over a wide range of output voltages.

[0101] Next, a modification of the switch circuit 100 will be described.

[0102] 6 is a circuit diagram of a switch circuit 100A according to a modified example. In this modified example, a first current detection circuit 130A includes a level shifter 132. The level shifter 132 shifts down the levels of the source voltage Vs and the output voltage Vout of the replica transistor 104. The level shifter 132 is configured to be able to independently adjust the amount of level shift of the source voltage Vs and the output voltage Vout.

[0103] By adding the level shifter 132, the influence of variations in the gate threshold voltage of the main transistor 102 and the gate threshold voltage of the replica transistor 104 can be canceled.

[0104] The first amplifier AMP1 is configured to have an adjustable input offset voltage, which reduces the error between the drain-source voltage of the replica transistor and the drain-source voltage of the main transistor, enabling accurate current detection.

[0105] 7 is a circuit diagram showing an example of the configuration of the level shifter 132 and the first amplifier AMP1. The bipolar transistor Q1, resistors R11 and R12, and variable current source CS1 level-shift down the output voltage VOUT. The output voltage VOUT' after the level shift is VOUT'=VOUT-Vbe1-Ic1·R11 Vbe1 is the base-emitter voltage of the bipolar transistor Q1, and Ic1 is the current Ic1 generated by the variable current source CS1.

[0106] The bipolar transistor Q2, resistors R21 and R22, and variable current source CS2 level-shift down the source voltage VS of the replica transistor 104. The source voltage VS' after the level shift is expressed as follows: VS' = VS - Vbe2 - Ic2 · R21 Vbe2 is the base-emitter voltage of bipolar transistor Q2, and Ic2 is the current Ic2 generated by variable current source CS1.

[0107] By adjusting the current amounts Ic1 and Ic2 of the current sources CS1 and CS2, the level shift amounts can be adjusted independently.

[0108] The first amplifier AMP1 has an input stage 200 and a gain stage 210. The input stage 200 includes a tail current source 202, a differential pair 204 including transistors M11 and M12, bias transistors M13 and M14, a load 206 including resistors R11 and R12, and variable current sources CS3 and CS4. A bias voltage BIAS generated by the level shifter 132 is supplied to the gates of the bias transistors M13 and M14.

[0109] By adjusting the current amounts of the variable current sources CS3 and CS4, the input offset voltage of the first amplifier AMP1 can be canceled, and the drain-source voltage of the main transistor 102 and the drain-source voltage of the replica transistor 104 can be made to match accurately.

[0110] Although the embodiments of the present disclosure have been described using specific terms, this description is merely an example to facilitate understanding and does not limit the scope of the present disclosure or the claims, and the scope of the present invention is defined by the claims. Furthermore, not only the embodiments but also embodiments, examples, and modifications not described herein are included in the scope of the present invention.

[0111] (Addendum) The present disclosure discloses the following techniques.

[0112] (Item 1) A switch circuit, input and output terminals; an N-type main transistor connected between the input terminal and the output terminal; a replica transistor having the same configuration as the main transistor, the drain of which is connected to the input terminal, the gate of which is connected to the gate of the main transistor, and the source of which is connected to ground via a current limiting resistor; an output voltage monitoring circuit that compares the output voltage generated at the output terminal with a predetermined threshold voltage and generates a voltage detection signal that has a first level when the output voltage is higher than the threshold voltage and a second level when the output voltage is lower than the threshold voltage; a first current detection circuit including a first transistor connected to the source of the replica transistor, and a first amplifier that controls the first transistor so that the source voltage of the replica transistor approaches the source voltage of the main transistor when the voltage detection signal is at the first level, and turns off the first transistor when the voltage detection signal is at the second level, and that generates a first current detection signal proportional to the current flowing through the first transistor; a second current detection circuit including a first resistor and a first switch connected in series between the source of the replica transistor and ground, the first switch being off when the voltage detection signal is at the first level and the first switch being on when the voltage detection signal is at the second level, and generating a second current detection signal proportional to the current flowing through the first resistor; a current limiting circuit that adjusts a gate voltage of the main transistor in response to the first current detection signal when the voltage detection signal is at the first level, and adjusts a gate voltage of the main transistor in response to the second current detection signal when the voltage detection signal is at the second level; A switch circuit comprising:

[0113] (Item 2) The current limiting circuit feedback-controlling the gate voltage of the main transistor so that the first current detection signal does not exceed a reference voltage when the voltage detection signal is at the first level; 2. The switch circuit according to item 1, wherein the gate voltage of the main transistor is feedback-controlled so that the second current detection signal does not exceed the reference voltage when the voltage detection signal is at the second level.

[0114] (Item 3) The current limiting circuit a second transistor and a second resistor connected in series between the gate of the main transistor and ground; a second amplifier having an output connected to the gate of the second transistor and having one input terminal to which the first current detection signal is input when the voltage detection signal is at the first level and to which the second current detection signal is input when the voltage detection signal is at the second level; Item 3. The switch circuit according to item 2, comprising:

[0115] (Item 4) 4. The switch circuit according to any one of items 1 to 3, further comprising: a third resistor connected in series with the first transistor; and a third amplifier that amplifies a voltage drop across the third resistor and generates a third current detection signal, wherein the switch circuit further comprises a first protection circuit that turns off the main transistor when the third current detection signal exceeds a first threshold voltage while the voltage detection signal is at the first level.

[0116] (Item 5) 5. The switch circuit according to item 4, wherein the first protection circuit compares a fourth current detection signal corresponding to the voltage drop across the first resistor with a second threshold voltage when the voltage detection signal is at the second level, and turns off the main transistor when the fourth current detection signal exceeds the second threshold voltage.

[0117] (Item 6) 4. The switch circuit according to any one of items 1 to 3, further comprising a first protection circuit that compares a fourth current detection signal corresponding to a voltage drop across the first resistor with a second threshold voltage when the voltage detection signal is at the second level, and turns off the main transistor when the fourth current detection signal exceeds the second threshold voltage.

[0118] (Item 7) 7. The switch circuit according to item 5 or 6, wherein the fourth current detection signal is the same signal as the second current detection signal.

[0119] (Item 8) 8. The switch circuit according to any one of items 5 to 7, wherein the first threshold voltage is a constant voltage, and the second threshold voltage is dependent on the output voltage.

[0120] (Item 9) 9. The switch circuit according to any one of items 1 to 8, further comprising a second protection circuit that turns off the main transistor when a difference between the source voltage and the output voltage of the replica transistor exceeds a predetermined threshold voltage.

[0121] (Item 10) 10. The switch circuit of claim 9, wherein the second current detection circuit further includes a fourth resistor connected between the source of the replica transistor and the first switch.

[0122] (Item 11) the first current detection circuit further includes a level shifter that level-shifts the source voltage and the output voltage of the replica transistor; 11. The switch circuit according to any one of items 1 to 10, wherein the level shifter is capable of independently adjusting the shift amounts of the source voltage and the output voltage of the replica transistor.

[0123] (Item 12) 12. The switch circuit according to any one of items 1 to 11, wherein the first amplifier has an adjustable input offset voltage.

[0124] (Item 13) 13. The switch circuit according to any one of items 1 to 12, which is integrated on a single semiconductor substrate. [Explanation of symbols]

[0125] 2. System 4 Power circuit 6 Load circuit C1 smoothing capacitor 100 Switch Circuit 102 Main transistor 104 Replica Transistor 110 Switch control section 112 Charge pump circuit 114 Gate Driver 120 Output voltage monitor circuit 130 First current detection circuit M1 First transistor AMP1 First amplifier 132 Level Shifter RILIM Current limiting resistor 140 Second current detection circuit SW1 First switch R1 First resistor 150 Current limiting circuit AMP2 Second amplifier SEL1 Selector R3 3rd resistor 160 1st protection circuit R2 2nd resistor AMP3 Third amplifier SEL1, SEL2 selector 162 Comparator 170 2nd protection circuit

Claims

1. A switch circuit, input terminals and output terminals; an N-type main transistor connected between the input terminal and the output terminal; a replica transistor having the same configuration as the main transistor, the drain of which is connected to the input terminal, the gate of which is connected to the gate of the main transistor, and the source of which is connected to ground via a current limiting resistor; an output voltage monitoring circuit that compares the output voltage generated at the output terminal with a predetermined threshold voltage and generates a voltage detection signal that has a first level when the output voltage is higher than the threshold voltage and a second level when the output voltage is lower than the threshold voltage; a first current detection circuit including: a first transistor connected to the source of the replica transistor; and a first amplifier that controls the first transistor so that the source voltage of the replica transistor approaches the source voltage of the main transistor when the voltage detection signal is at the first level, and turns off the first transistor when the voltage detection signal is at the second level, and that generates a first current detection signal proportional to the current flowing through the first transistor; a second current detection circuit including a first resistor and a first switch connected in series between the source of the replica transistor and ground, the first switch being off when the voltage detection signal is at the first level and the first switch being on when the voltage detection signal is at the second level, and generating a second current detection signal proportional to the current flowing through the first resistor; a current limiting circuit that adjusts a gate voltage of the main transistor in response to the first current detection signal when the voltage detection signal is at the first level, and adjusts a gate voltage of the main transistor in response to the second current detection signal when the voltage detection signal is at the second level; A switch circuit comprising:

2. The current limiting circuit feedback-controlling the gate voltage of the main transistor so that the first current detection signal does not exceed a reference voltage when the voltage detection signal is at the first level; 2. The switch circuit according to claim 1, wherein the gate voltage of the main transistor is feedback-controlled so that the second current detection signal does not exceed the reference voltage when the voltage detection signal is at the second level.

3. The current limiting circuit a second transistor and a second resistor connected in series between the gate of the main transistor and ground; a second amplifier having an output connected to the gate of the second transistor and having one input terminal to which the first current detection signal is input when the voltage detection signal is at the first level and to which the second current detection signal is input when the voltage detection signal is at the second level; The switch circuit of claim 2 , comprising:

4. 4. The switch circuit according to claim 1, further comprising: a third resistor connected in series with the first transistor; and a third amplifier that amplifies a voltage drop across the third resistor to generate a third current detection signal, wherein a first protection circuit turns off the main transistor when the third current detection signal exceeds a first threshold voltage while the voltage detection signal is at the first level.

5. 5. The switch circuit according to claim 4, wherein when the voltage detection signal is at the second level, the first protection circuit compares a fourth current detection signal corresponding to a voltage drop across the first resistor with a second threshold voltage, and turns off the main transistor when the fourth current detection signal exceeds the second threshold voltage.

6. 4. The switch circuit according to claim 1, further comprising: a first protection circuit that compares a fourth current detection signal corresponding to a voltage drop across the first resistor with a second threshold voltage when the voltage detection signal is at the second level, and turns off the main transistor when the fourth current detection signal exceeds the second threshold voltage.

7. 6. The switch circuit according to claim 5, wherein the fourth current detection signal is the same signal as the second current detection signal.

8. 6. The switch circuit according to claim 5, wherein the first threshold voltage is a constant voltage, and the second threshold voltage is dependent on the output voltage.

9. 4. The switch circuit according to claim 1, further comprising a second protection circuit that turns off the main transistor when a difference between the source voltage and the output voltage of the replica transistor exceeds a predetermined threshold voltage.

10. 10. The switch circuit according to claim 9, wherein the second current detection circuit further includes a fourth resistor connected between the source of the replica transistor and the first switch.

11. the first current detection circuit further includes a level shifter that level-shifts the source voltage and the output voltage of the replica transistor; 4. The switch circuit according to claim 1, wherein the level shifter is capable of independently adjusting the amounts of shift of the source voltage and the output voltage of the replica transistor.

12. 4. The switch circuit according to claim 1, wherein the first amplifier has an adjustable input offset voltage.

13. 4. The switch circuit according to claim 1, which is integrated on a single semiconductor substrate.

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