Switch control circuit, universal bus control circuit and method for controlling power switch

Abstract

The present application discloses a switch control circuit, a universal bus control circuit, and a method for controlling a power switch; the switch control circuit includes a power switch, a first protection unit, and a second protection unit. The power switch has a first end coupled to a first voltage end to receive a first voltage, a second end coupled to a second voltage end to receive a second voltage, and a control end for receiving a control voltage. In a first mode, the control voltage is greater than the first voltage so that at least one transistor in the power switch is fully turned on. In a second mode, when the voltage at the second voltage end is less than a first reference voltage, the first protection unit pulls down the control voltage to reduce the current conducted by the power switch. When the voltage at the second voltage end is less than the second reference voltage, the second protection unit pulls down the control voltage to a ground voltage, thereby turning off at least one transistor in the power switch.

Description

Technical Field

[0001] The present application relates to a switch control circuit, and more particularly to a switch control circuit with a short-circuit protection mechanism. Background Art

[0002] Power switches are often used to control the current flow between two endpoints. To handle higher currents, power switches typically utilize transistors with high current-carrying capacity and low on-resistance. Furthermore, depending on the application, the voltage across the power switch may vary during operation, and the power switch may be turned on or off in response to these voltage changes, depending on system requirements. For example, when the voltage difference across the power switch increases, the system may turn off the power switch as a short-circuit protection mechanism to prevent excessive current flow and damage to components in the circuit.

[0003] However, the metal lines used to transmit voltage may have inductive characteristics. Therefore, when the voltage changes, if the control voltage is immediately converted from a high voltage to a low voltage to turn off the transistor in the power switch, the equivalent inductance of the metal line will continue to output current to the drain of the transistor, and a large amount of charge will instantly accumulate in the drain of the transistor. In this case, the charge accumulated in the drain of the transistor will cause the drain voltage to increase rapidly. When the drain-gate voltage of the transistor exceeds the withstand voltage that the transistor can withstand, it will cause damage to the transistor, resulting in the power switch not being able to operate normally. Therefore, how to effectively and safely provide a short-circuit protection mechanism has become a problem to be solved. Summary of the Invention

[0004] An embodiment of the present application provides a switch control circuit comprising a first voltage terminal, a second voltage terminal, a power switch, a first protection unit, and a second protection unit.

[0005] The first voltage terminal is used to receive a first voltage. The second voltage terminal is used to receive a second voltage, wherein the second voltage is greater than the second voltage in the second mode. The power switch has a first terminal, a second terminal, and a control terminal, the first terminal of the power switch is coupled to the first voltage terminal, the second terminal of the power switch is coupled to the second voltage terminal, and the control terminal of the power switch is used to receive a control voltage. The power switch includes at least one transistor, wherein in the first mode, the control voltage is greater than the first voltage so that the at least one transistor in the power switch is fully turned on. The first protection unit is coupled to the control terminal and the second voltage terminal of the power switch, and is used to compare the voltage of the second voltage terminal with a first reference voltage. In the second mode, when the voltage of the second voltage terminal is less than the first reference voltage, the first protection unit pulls down the control voltage to reduce the current conducted by the at least one transistor in the power switch. The second protection unit is coupled to the control terminal and the second voltage terminal of the power switch, and is configured to compare the voltage of the second voltage terminal with a second reference voltage. In a second mode, when the voltage of the second voltage terminal is less than the second reference voltage, the second protection unit turns on a discharge path to pull the control voltage down to ground, thereby turning off the at least one transistor in the power switch. The first reference voltage is greater than the second reference voltage.

[0006] Another embodiment of the present application provides a universal bus control circuit, comprising a universal serial bus (USB) interface and the switch control circuit, wherein the first voltage terminal is coupled to a first pin of the USB interface to receive the first voltage, and the second voltage terminal is coupled to a second pin of the USB interface to receive the second voltage.

[0007] Another embodiment of the present application provides a method for controlling a power switch, wherein the power switch has a first terminal and a second terminal, the first terminal of the power switch being configured to receive a first voltage, and the second terminal of the power switch being configured to receive a second voltage, the power switch including at least one transistor, and the first voltage being greater than the second voltage. The method includes, in a first mode, generating a control voltage to the control terminal of the at least one transistor to turn on the at least one transistor, wherein the control voltage is greater than the first voltage. In a second mode, the second voltage is pulled down to a ground voltage. During the process of pulling the second voltage down to the ground voltage, when the voltage at the second terminal of the power switch is less than a first reference voltage, the control voltage is lowered to reduce the current conducted by the at least one transistor in the power switch, and when the voltage at the second terminal of the power switch is less than a second reference voltage, the control voltage is pulled down to the ground voltage to turn off the at least one transistor in the power switch. The first reference voltage is greater than the second reference voltage.

[0008] The switch control circuit, universal bus control circuit, and method for controlling a power switch provided in the present application can phase-wise shut off the power switch when a short circuit event is about to occur. This can avoid the problem of the power switch being turned off too quickly, causing the terminal voltage to be too high or too low, thereby damaging circuit components, and can achieve a short-circuit protection effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 FIG. 1 is a schematic diagram of a universal bus control circuit according to an embodiment of the present application.

[0010] Figure 2 yes Figure 1 The voltage and current change timing diagram inside the switch control circuit.

[0011] Figure 3 is a schematic diagram of a switch control circuit according to another embodiment of the present application.

[0012] Figure 4 is a flow chart of a method for controlling a power switch according to an embodiment of the present invention.

[0013] Explanation of symbols:

[0014] 10: Universal bus control circuit

[0015] 12: Universal bus interface

[0016] 100,200: switch control circuit

[0017] 110,210: Power switch

[0018] 120,220: First protection unit

[0019] 122: First comparator

[0020] 130,230: Second protection unit

[0021] 132: Second comparator

[0022] 140,240: Charge pump

[0023] 300: Method

[0024] C1: first capacitor

[0025] C2: Second capacitor

[0026] I1: current

[0027] M1A, M1B: first transistor

[0028] M2A: Second transistor

[0029] M3A: The third transistor

[0030] M4A: The fourth transistor

[0031] M5A: The fifth transistor

[0032] M6A: Sixth transistor

[0033] N1: The first terminal of the power switch

[0034] N2: The second end of the power switch

[0035] N3: Control terminal of power switch

[0036] P1: first pin

[0037] P2: second pin

[0038] PI1: First voltage terminal

[0039] PI2: Second voltage terminal

[0040] S310 to S340: Steps

[0041] T1, T2: Time period

[0042] T2A, T2B: time point

[0043] VCP: Control voltage

[0044] VD1, VD2, VP2: voltage

[0045] VREF 1: First reference voltage

[0046] VREF2: Second reference voltage

[0047] VTH4: threshold voltage DETAILED DESCRIPTION

[0048] Figure 1 FIG2 is a schematic diagram of a universal bus control circuit 10 according to an embodiment of the present application. The universal bus control circuit 10 may include a universal serial bus (USB) interface 12 and a switch control circuit 100. The USB interface 12 may include multiple pins required by the universal bus, and the switch control circuit 100 may be used to control the current between a first pin P1 and a second pin P2.

[0049] like Figure 1As shown, the switch control circuit 100 may include a first voltage terminal PI1, a second voltage terminal PI2, and a power switch 110. The first voltage terminal PI1 may be coupled to the first pin P1 of the universal serial bus interface 12 to receive a first voltage V1, and the second voltage terminal PI1 may be coupled to the second pin P2 of the universal serial bus interface 12 to receive a second voltage V2. Furthermore, the power switch 110 has a first terminal N1, a second terminal N2, and a control terminal N3. The first terminal N1 of the power switch 110 may be coupled to the first voltage terminal PI1, the second terminal N2 of the power switch 110 may be coupled to the second voltage terminal PI2, and the control terminal N3 of the power switch 110 may receive a control voltage VCP. In this embodiment, the power switch 110 may include a first transistor M1A and a second transistor M2A. The first transistor M1A has a first terminal, a second terminal, and a control terminal. The first terminal of the first transistor M1A may be coupled to the first terminal N1 of the power switch 110, and the control terminal of the first transistor M1A may be coupled to the control terminal N3 of the power switch 110. The second transistor M2A has a first terminal, a second terminal, and a control terminal. The first terminal of the second transistor M2A can be coupled to the second terminal of the first transistor M1A, the second terminal of the second transistor M2A can be coupled to the second terminal N2 of the power switch 110, and the control terminal of the second transistor M2A can be coupled to the control terminal N3 of the power switch 110. In other words, the switch control circuit 100 can control the degree of conductivity of the first transistor M1A and the second transistor M2A by adjusting the magnitude of the control voltage VCP, thereby turning on or off the power switch 110.

[0050] In this embodiment, the USB interface 12 may be, for example, a Type-C USB interface, wherein the first pin P1 may be, for example, a power (VCONN) pin, and the second pin P2 may be a Configuration Channel (CC) pin. In this case, the second pin P2 may operate at different voltages depending on the application mode to allow the system to identify the current application mode. In other words, in different modes, the second voltage V2 may have different voltage values, and the switch control circuit 100 may control the power switch 110 to correspondingly open or close the current path between the first voltage terminal PI1 and the second voltage terminal PI2.

[0051] For example, in the first mode, the first voltage V1 may be approximately 5V, and the second voltage V2 may be slightly lower than the first voltage V1, such as approximately 4.9V. In this case, the power switch 110 may be turned on, and the current I1 may flow from the first voltage terminal PI1 to the second voltage terminal PI2. However, in the second mode, the second voltage V2 is pulled down to ground. In other words, the second voltage V2 in the first mode is greater than the second voltage V2 in the second mode. Therefore, when switching from the first mode to the second mode, the voltage difference between the first voltage terminal PI1 and the second voltage terminal PI2 increases accordingly. In this case, to prevent the excessive current I1 from damaging the transistors M1A and M2A in the power switch 110, the switch control circuit 100 may turn off the power switch 110.

[0052] In this embodiment, the switch control circuit 100 may further include a first capacitor C1 and a second capacitor C2. The first capacitor C1 may have a first end and a second end. The first end of the first capacitor C1 may be coupled to the first voltage terminal PI1, and the second end of the first capacitor C1 may be coupled to the ground voltage. The second capacitor C2 may have a first end and a second end. The first end of the second capacitor C2 may be coupled to the second voltage terminal PI2, and the second end of the second capacitor C2 may be coupled to the ground voltage. The first capacitor C1 and the second capacitor C2 can reduce the drastic fluctuations in the voltages of the first voltage terminal PI1 and the second voltage terminal PI2 as the first voltage V1 and the second voltage V2 change, thereby making the voltages of the first voltage terminal PI1 and the second voltage terminal PI2 more stable.

[0053] Furthermore, in this embodiment, the first voltage terminal PI1 and the second voltage terminal PI2 can be coupled to the first pin P1 and the second pin P2 of the universal serial bus interface 12, respectively, via circuitry external to the switch control circuit 100 to receive the first voltage V1 and the second voltage V2. For example, the switch control circuit 100 and the universal serial bus interface 12 may be connected via metal bonding wires within the chip package. Because metal bonding wires or other external circuitry often have inductive properties, when the power switch 110 is turned off, the current originally flowing from the first pin P1 into the first voltage terminal PI1 does not instantly disappear. Instead, charge continues to accumulate in the first voltage terminal PI1, thereby increasing the voltage of the first voltage terminal PI1. In this case, if the control voltage VCP received by the control terminal of transistor M1A is directly pulled down to ground, the drain-gate voltage of transistor M1A may become excessively high, potentially damaging transistor M1A. Furthermore, in Type-C USB applications, to improve charging performance, a higher current, such as 1.5 amps or 3 amps, may flow through the first pin P1. In this case, the transistor M1A may be more severely damaged.

[0054] Similarly, when the power switch 110 is turned off, the current originally flowing from the second voltage terminal PI2 into the second pin P2 does not disappear instantly. Instead, it continues to draw charge from the second voltage terminal PI2, causing the voltage of the second voltage terminal PI2 to continue to drop. In this case, if the voltage of the second voltage terminal PI2 drops to a negative voltage, it may significantly affect the stability of the system and even cause the system to malfunction.

[0055] To prevent circuit damage caused by the power switch 110 being instantly turned off in the second mode, which may result in the voltage of the first voltage terminal PI1 being too high or the voltage of the second voltage terminal PI1 being too low, the switch control circuit 100 can use the first protection unit 120 and the third protection unit 130 to gradually turn off the power switch 110 in a staged manner.

[0056] Figure 2 It is a timing diagram of the voltage and current changes inside the switch control circuit 100. Figure 2 During the first time period T1, the switch control circuit 100 operates in the first mode. During this time, the control voltage VCP is significantly greater than the first voltage V1. For example, the first voltage V1 may be 5V, while the control voltage VCP may be 10V. Therefore, transistors M1A and M2A in the power switch 110 are fully turned on. In this embodiment, to generate a control voltage VCP higher than the first voltage V1, the switch control circuit 100 further includes a charge pump 140 to generate the control voltage VCP.

[0057] exist Figure 2 During time period T2, the switch control circuit 100 operates in the second mode. During this time period, the second voltage V2 is pulled down to ground, and the voltage VP2 at the second voltage terminal PI2 gradually decreases, causing the current I1 flowing through the current switch 110 to gradually increase. In this embodiment, the first protection unit 130 can be coupled to the control terminal N3 and the second voltage terminal PI2 of the power switch 110 and can continuously compare the voltage VP2 at the second voltage terminal PI2 with the first reference voltage VREF1. At time point T2A, when the voltage VP2 at the second voltage terminal PI2 is less than the first reference voltage VREF1, the first protection unit 130 pulls down the control voltage VCP to reduce the current I1 conducted by transistors M1A and M2A in the power switch 110.

[0058] Furthermore, if Figure 1As shown, the second protection unit 130 can be coupled to the control terminal N3 and the second voltage terminal PI2 of the power switch 110, and can continuously compare the voltage at the second voltage terminal PI2 with the second reference voltage VREF2. In this embodiment, the first reference voltage VREF1 is greater than the second reference voltage VREF2. Therefore, as the voltage VP2 at the second voltage terminal PI2 is gradually pulled down, the first protection unit 120 is first triggered to pull down the control voltage VCP. At time T2B, after time T2A, when the voltage VP2 at the second voltage terminal PI2 is less than the second reference voltage VREF2, the second protection unit 130 activates the discharge path to pull down the control voltage VCP to the ground voltage, thereby turning off the transistors M1A and M2A in the power switch 110.

[0059] That is to say, during the time period from time point T2A to T2B, when the first protection unit 120 is triggered to reduce the control voltage VCP, and the second protection unit 130 is not triggered, the power switch 110 will not be directly cut off. In this case, during the time period from time point T2A to T2B, the current flowing from the first pin P1 into the first voltage terminal PI1 can still flow through the power switch 110 to the second voltage terminal PI2 and the second pin P2, thereby avoiding the aforementioned problem of the voltage at the first voltage terminal PI1 being too high and the voltage at the second voltage terminal PI2 being too low. In addition, since the first protection unit 130 can pull down the control voltage VCP to a lower voltage value, the on-resistance of the transistors M1A and M2A will also increase accordingly, thereby avoiding the current I1 being too large and achieving the effect of short-circuit protection. In addition, Figure 2 In the embodiment, since the external circuit coupled to the second voltage terminal PI2 has an inductor characteristic, an undershoot may occur before the second voltage V2 is pulled down and stabilized to the ground voltage.

[0060] like Figure 1As shown, the first protection unit 120 may include a first comparator 122, a third transistor M3A, a fourth transistor M4A, and a fifth transistor M5A. The first comparator 122 has a first input terminal, a second input terminal, and an output terminal. The first input terminal of the first comparator 122 may be coupled to a first reference voltage VREF1, and the second input terminal of the first comparator 122 may be coupled to a second voltage terminal PI2. The third transistor M3A has a first terminal, a second terminal, and a control terminal. The first terminal of the third transistor M3A may be coupled to a ground voltage, and the control terminal of the third transistor M3A may be coupled to the output terminal of the first comparator 122. The fourth transistor M4A has a first terminal, a second terminal, and a control terminal. The first terminal of the fourth transistor M4A may be coupled to the second terminal of the third transistor M3B, and the control terminal of the fourth transistor M4A may be coupled to the second voltage terminal PI2. The fifth transistor M5A has a first terminal, a second terminal, and a control terminal. The first terminal of the fifth transistor M5A can be coupled to the second terminal of the fourth transistor M4A, the second terminal of the fifth transistor M5A can be coupled to the control terminal of the power switch 110, and the control terminal of the fifth transistor M5A can be coupled to the first terminal N1 of the power switch 110.

[0061] In this embodiment, the first transistor M1A, the second transistor M2A, the third transistor M3A and the fifth transistor M5A may be N-type transistors, and the fourth transistor M4A may be a P-type transistor. Figure 2 As shown, when the voltage VP2 of the second voltage terminal PI2 is less than the first reference voltage VREF1, the voltage VD1 of the output terminal of the first comparator 122 changes from a low voltage to a high voltage, causing the third transistor M3A to be turned on, and the fifth transistor M5A and the fourth transistor M4A to be turned on, thereby pulling down the control voltage VCP generated by the charge pump 140 to increase the on-resistance of the transistors M1A and M2A and weaken the intensity of the current I1. However, if the control voltage VCP is pulled down to a value lower than the voltage VP2 of the second voltage terminal PI2 plus the threshold voltage VTH4 of the fourth transistor M4A, the fourth transistor M4A will be turned off. Therefore, the first protection circuit 120 can maintain the control voltage VCP at a voltage value higher than the voltage VP2 of the second voltage terminal PI2 by a threshold voltage VTH4, as shown in FIG. Figure 2 In this case, if the absolute value of the threshold voltage VTH4 of the fourth transistor M4A is greater than the absolute values ​​of the threshold voltages of the transistors M1A and M2A in the power switch 110, the transistors M1A and M2A can be maintained in an on state to prevent the power switch 110 from being turned off too quickly, thereby preventing the first voltage terminal PI1 from being too high and the second voltage terminal PI2 from being too low.

[0062] In this embodiment, because the transistors M1A and M2A in the power switch 110 need to transmit a relatively large current, transistors with a relatively large channel width are generally required. In contrast, because the charge pump 140 generally has a relatively weak load withdrawal capability, the third transistor M3A, the fourth transistor M4A, and the fifth transistor M5A can use transistors with relatively small channel widths. In other words, the channel widths of the transistors M1A and M2A can be larger than the channel widths of the third transistor M3A, the fourth transistor M4A, and the fifth transistor M5A. Generally speaking, in this case, the absolute values ​​of the threshold voltages of the transistors M1A and M2A will also be smaller than the absolute values ​​of the threshold voltages of the third transistor M3A, the fourth transistor M4A, and the fifth transistor M5A, thereby meeting the aforementioned requirements.

[0063] In addition, if Figure 1 As shown, the second protection unit 130 may include a second comparator 132 and a sixth transistor M6A. The second comparator 120 has a first input terminal, a second input terminal, and an output terminal. The first input terminal of the second comparator 120 may be coupled to the second reference voltage VREF2, and the second input terminal of the second comparator 120 may be coupled to the second voltage terminal PI2. The sixth transistor M6A has a first terminal, a second terminal, and a control terminal. The first terminal of the sixth transistor M6A may be coupled to the ground voltage, the second terminal of the sixth transistor M6A may be coupled to the control terminal N3 of the power switch 110, and the control terminal of the sixth transistor M6A may be coupled to the output terminal of the second comparator 132.

[0064] In this case, if Figure 2 As shown, when the voltage VP2 of the second voltage terminal PI2 continues to decrease and becomes less than the second reference voltage VREF2 at time point T2B, the voltage VD2 of the output terminal of the second comparator 132 changes from a low voltage to a high voltage, so that the sixth transistor M6A is turned on and the control voltage VCP is pulled down to the ground voltage.

[0065] Since the switch control circuit 100 can use the first protection unit 120 and the second protection unit 130 to turn off the power switch 110 in a staged manner, the problem of the power switch 110 being turned off too quickly, which would cause the first voltage terminal PI1 to be too high and the second voltage terminal PI2 to be too low, can be avoided, and a short circuit protection effect can be achieved.

[0066] In some embodiments, the switch control circuit 100 may also operate in other modes besides the first mode and the second mode. In some modes, the second voltage V2 may be higher than the first voltage V1. Figure 1In an embodiment, the second end of the first transistor M1A may be the source end of the first transistor M1A, and the first end of the second transistor M2A may be the source end of the second transistor M2A. In other words, the source ends of the first transistor M1A and the second transistor M2A may be connected to meet the requirements of different operating modes. However, the present application is not limited to this. In some embodiments, the second end of the first transistor M1A may be the drain end of the first transistor M1A, and the first end of the second transistor M2A may be the drain end of the second transistor M2A. In other words, the drain ends of the first transistor M1A and the second transistor M2A may be connected.

[0067] Furthermore, in this embodiment, the power switch 110 may include transistors M1A and M2A, wherein the first transistor M1A may be a low-voltage transistor and the second transistor M2A may be a high-voltage transistor. However, the present application is not limited thereto. In some other embodiments, the power switch 110 may include only one transistor.

[0068] Figure 3 FIG2 is a schematic diagram of a switch control circuit 200 according to another embodiment of the present application. The switch control circuit 200 has a similar structure to the switch control circuit 100 and operates according to the same principles. However, the power switch 210 of the switch control circuit 200 only includes a first transistor M1B. The first transistor M1B has a first terminal, a second terminal, and a control terminal. The first terminal of the first transistor M1B is coupled to the first terminal N1 of the power switch 210, the second terminal of the first transistor M1B is coupled to the second terminal N2 of the power switch 210, and the control terminal of the first transistor M1B is coupled to the control terminal N3 of the power switch 210.

[0069] exist Figure 3 In this embodiment, the switch control circuit 200 can phase-pull down the control voltage VCP generated by the charge pump 240 to the ground voltage via the first protection unit 220 and the second protection unit 230 during the process of the voltage VP2 at the second voltage terminal PI2 changing from a high voltage to a low voltage. This can avoid the problem of the power switch 210 being turned off too quickly, resulting in the voltage at the first voltage terminal PI1 being too high and the voltage at the second voltage terminal PI2 being too low, and can achieve short-circuit protection. In this embodiment, the switch control circuits 100 and 200 can be applied to the universal bus control circuit 10. However, the present application is not limited thereto. In other embodiments, the switch control circuits 100 and 200 can also be applied to other power switch circuits requiring short-circuit protection.

[0070] Figure 4 FIG. 3 is a flow chart of a method 300 for controlling a power switch according to an embodiment of the present invention. The method 300 includes steps S310 to S340. In some embodiments, the method 300 may be used to control the power switch 110, such as Figure 1 As shown, the first terminal N1 of the power switch 110 may be coupled to the first voltage terminal PI1 to receive the first voltage V1 , and the second terminal N2 of the power switch 110 may be coupled to the second voltage terminal PI2 to receive the second voltage V2 .

[0071] In step S310, the power switch 110 operates in the first mode. During this operation, a high-voltage control voltage VCP is provided to turn on transistors M1A and M2A in the power switch 110. Next, in step S320, the second voltage V2 received by the power switch 110 begins to be pulled down, placing the power switch 110 in the second mode. While the second voltage V2 is being pulled down to ground, if the second terminal N2 of the power switch 110 falls below the first reference voltage VREF1, the first protection unit 120 executes step S330 to reduce the control voltage VCP, keeping the power switch 110 on while also reducing the current it conducts. Subsequently, when the voltage at the second terminal N2 of the power switch 110 falls below the second reference voltage VREF2, the second protection unit 130 pulls the control voltage VCP down to ground, turning off the power switch 110.

[0072] In summary, the switch control circuit, universal bus control circuit, and method for controlling a power switch provided in the present application can phase-wise turn off the power switch when a short circuit event is about to occur. This can avoid the problem of the power switch being turned off too quickly, causing the terminal voltage to be too high or too low, thereby causing damage to circuit components, and can achieve the effect of short-circuit protection.

Claims

1. A switch control circuit, characterized in that: Include: a first voltage terminal for receiving a first voltage; a second voltage terminal for receiving a second voltage, wherein the second voltage in a first mode is greater than the second voltage in a second mode; a power switch having a first terminal coupled to the first voltage terminal, a second terminal coupled to the second voltage terminal, and a control terminal for receiving a control voltage, the power switch comprising at least one transistor, wherein in a first mode, the control voltage is greater than the first voltage so that the at least one transistor in the power switch is fully turned on; a first protection unit coupled to the control terminal and the second voltage terminal of the power switch, configured to compare the voltage of the second voltage terminal with a first reference voltage, and in the second mode, when the voltage of the second voltage terminal is less than the first reference voltage, pull down the control voltage to reduce a current conducted by the at least one transistor in the power switch; and a second protection unit coupled to the control terminal and the second voltage terminal of the power switch, configured to compare the voltage of the second voltage terminal with a second reference voltage, and, in the second mode, when the voltage of the second voltage terminal is less than the second reference voltage, conduct a discharge path to pull down the control voltage to a ground voltage, thereby turning off the at least one transistor in the power switch; The first reference voltage is greater than the second reference voltage.

2. The switch control circuit according to claim 1, wherein: The power switch includes a first transistor having a first terminal coupled to the first terminal of the power switch, a second terminal coupled to the second terminal of the power switch, and a control terminal coupled to the control terminal of the power switch.

3. The switch control circuit according to claim 1, wherein: The power switch includes: a first transistor having a first terminal coupled to the first terminal of the power switch, a second terminal, and a control terminal coupled to the control terminal of the power switch; and A second transistor has a first terminal coupled to the second terminal of the first transistor, a second terminal coupled to the second terminal of the power switch, and a control terminal coupled to the control terminal of the power switch.

4. The switch control circuit according to claim 3, wherein: The second terminal of the first transistor is a source terminal of the first transistor, and the first terminal of the second transistor is a source terminal of the second transistor; or The second terminal of the first transistor is a drain terminal of the first transistor, and the first terminal of the second transistor is a drain terminal of the second transistor.

5. The switch control circuit according to claim 1, wherein: The first protection unit includes: a first comparator having a first input terminal coupled to the first reference voltage, a second input terminal coupled to the second voltage terminal, and an output terminal; a third transistor having a first terminal coupled to the ground voltage, a second terminal, and a control terminal coupled to the output terminal of the first comparator; a fourth transistor having a first terminal coupled to the second terminal of the third transistor, a second terminal, and a control terminal coupled to the second voltage terminal; and A fifth transistor has a first terminal coupled to the second terminal of the fourth transistor, a second terminal coupled to the control terminal of the power switch, and a control terminal coupled to the first terminal of the power switch.

6. The switch control circuit according to claim 5, wherein: The third transistor and the fifth transistor are N-type transistors, and the fourth transistor is a P-type transistor.

7. The switch control circuit according to claim 6, wherein: When the voltage of the second voltage terminal is lower than the first reference voltage, the output terminal of the first comparator changes from a low voltage to a high voltage, so that the third transistor is turned on, and the fourth transistor is used to reduce the control voltage to the voltage of the second voltage terminal plus a threshold voltage of the fourth transistor, so as to reduce the current conducted by the at least one transistor in the power switch; and An absolute value of a threshold voltage of the fourth transistor is greater than an absolute value of a threshold voltage of the at least one transistor in the power switch.

8. The switch control circuit according to claim 1, wherein: The second protection unit comprises: a second comparator having a first input terminal coupled to the second reference voltage, a second input terminal coupled to the second voltage terminal, and an output terminal; and A sixth transistor has a first terminal coupled to the ground voltage, a second terminal coupled to the control terminal of the power switch, and a control terminal coupled to the output terminal of the second comparator.

9. A universal bus control circuit, characterized in that: Include: a Universal Serial Bus (USB) interface; and The switch control circuit according to any one of claims 1 to 8, wherein the first voltage terminal is coupled to a first pin of a universal serial bus interface to receive the first voltage, and the second voltage terminal is coupled to a second pin of the universal serial bus interface to receive the second voltage.

10. A method for controlling a power switch, characterized in that: The power switch has a first terminal for receiving a first voltage and a second terminal for receiving a second voltage. The power switch includes at least one transistor, and the first voltage is greater than the second voltage. The method includes: In a first mode, generating a control voltage to a control terminal of the at least one transistor to turn on the at least one transistor, wherein the control voltage is greater than the first voltage; In a second mode, pulling the second voltage down to a ground voltage; In the process of the second voltage being pulled down to the ground voltage: When the voltage at the second terminal of the power switch is less than a first reference voltage, lowering the control voltage to reduce a current conducted by the at least one transistor in the power switch; and When the voltage at the second terminal of the power switch is less than a second reference voltage, pulling the control voltage down to the ground voltage to turn off the at least one transistor in the power switch; The first reference voltage is greater than the second reference voltage.

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