USB interface function protection circuit and terminal device

Abstract

The utility model discloses a USB interface function protection circuit and a terminal device, the USB interface function protection circuit is connected with a USB interface, a fast charging chip and a control circuit, the USB interface function protection circuit comprises a first-level protection module, a second-level protection module and a third-level protection module; the first-stage protection module is connected with the USB interface and the second-stage protection module, the second-stage protection module is connected with the third-stage protection module and the control circuit, and the third-stage protection module is connected with the fast charging chip; the first-stage protection module is used for performing first-stage surge prevention; the secondary protection module is used for carrying out secondary surge prevention, carrying out anti-burning port protection according to a first control signal output by the control circuit, and detecting the voltage value of the power supply voltage to carry out overvoltage protection; and the third-stage protection module carries out reverse connection prevention protection according to a second control signal output by the fast charging chip. The USB interface function protection circuit realizes surge prevention, reverse connection prevention, port burning prevention and overvoltage protection of the USB interface.

Description

Technical Field

[0001] The utility model relates to the field of electronic technology, and particularly relates to a USB interface function protection circuit and a terminal device. Background Art

[0002] When a mobile phone is inserted into a charger for charging, due to abnormal fluctuations in the power grid or abnormalities in the charger itself, a surge voltage and current may be generated on the power supply VBUS of the mobile phone's USB interface. Therefore, in order to verify the protection ability of the mobile phone against such abnormal surges, it is necessary to conduct a surge test on the USB interface, usually testing up to ±300V or higher voltages. In order to prevent damage to the mobile phone, surge protection measures need to be added. The conventional design is a circuit composed of a TVS (Transient Voltage Suppressor) and an OVP (Over Voltage Protection) chip. However, when the mobile phone requires high-current fast charging (Charger Pump charging, generally above 30W), an OVP chip with a large current is required, resulting in a high cost.

[0003] In addition, the USB interface of the mobile phone also needs to be designed with protection circuits such as reverse connection prevention, burn-proof port protection, and overvoltage protection.

[0004] Therefore, the existing technology still needs to be improved. Summary of the Utility Model

[0005] In view of the deficiencies of the above-mentioned existing technology, the purpose of the present utility model is to provide a USB interface function protection circuit and a terminal device to solve the problem that the existing USB interface does not have multiple protections.

[0006] In order to achieve the above purpose, the present utility model adopts the following technical solutions:

[0007] A USB interface function protection circuit is connected to a USB interface, a fast charging chip, and a control circuit, and includes a primary protection module, a secondary protection module, and a tertiary protection module; the primary protection module is connected to the USB interface and the secondary protection module, the secondary protection module is connected to the tertiary protection module and the control circuit, and the tertiary protection module is connected to the fast charging chip;

[0008] The primary protection module is used for primary surge protection;

[0009] The secondary protection module is used for secondary surge protection, burn-proof port protection according to the first control signal output by the control circuit, and also detects the voltage value of the power supply voltage for overvoltage protection;

[0010] The tertiary protection module performs reverse connection prevention protection according to the second control signal output by the fast charging chip.

[0011] In the described USB interface function protection circuit, the primary protection module includes a first TVS tube and a diode; the negative electrode of the first TVS tube is connected to the power supply pin of the USB interface, the negative electrode of the diode, and the secondary protection module; the positive electrode of the first TVS tube is connected to the ground pin of the USB interface, the positive electrode of the diode, and the secondary protection module.

[0012] In the described USB interface function protection circuit, the primary protection module further includes a first capacitor, one end of the first capacitor is connected to the negative electrode of the diode and the secondary protection module, and the other end of the first capacitor is connected to the positive electrode of the diode and the secondary protection module.

[0013] In the described USB interface function protection circuit, the secondary protection module includes a comparator, a first switching tube, a first resistor, a second resistor, a third resistor, and a second capacitor;

[0014] The inverting input terminal of the comparator is connected to one end of the first resistor and one end of the second resistor; the other end of the first resistor is connected to one end of the first capacitor, the source electrode of the first switching tube, one end of the second capacitor, and the tertiary protection module; the other end of the second resistor is connected to the ground pin of the USB interface, the non-inverting input terminal of the comparator inputs a reference voltage, the output terminal of the comparator is connected to the gate electrode of the first switching tube and one end of the third resistor, the other end of the third resistor inputs a first control signal, and the drain electrode of the first switching tube is connected to the ground pin of the USB interface and the other end of the second capacitor.

[0015] In the described USB interface function protection circuit, the secondary protection module further includes a second TVS tube, the positive electrode of the second TVS tube is connected to the output terminal of the comparator and the gate electrode of the first switching tube, and the negative electrode of the second TVS tube is connected to the other end of the first resistor and the source electrode of the first switching tube.

[0016] In the described USB interface function protection circuit, the secondary protection module further includes a fourth resistor, and the fourth resistor is connected in parallel with the second TVS tube.

[0017] In the described USB interface function protection circuit, the secondary protection module further includes a third capacitor, one end of the third capacitor is connected to the gate electrode of the first switching tube and the positive electrode of the second TVS tube, and the other end of the third capacitor is connected to the source electrode of the first switching tube and the negative electrode of the second TVS tube.

[0018] In the described USB interface function protection circuit, the tertiary protection module includes a second switching tube and a third switching tube, the drain electrode of the second switching tube is connected to the source electrode of the first switching tube, the source electrode of the second switching tube is connected to the source electrode of the third switching tube, and the gate electrode of the second switching tube is connected to the gate electrode of the third switching tube and inputs a second control signal; the drain electrode of the third switching tube is the voltage input terminal.

[0019] In the described USB interface function protection circuit, the three - level protection module further includes a fourth capacitor. One end of the fourth capacitor is connected to the drain of the third switching transistor, and the other end of the fourth capacitor is connected to the drain of the first switching transistor and the ground on the circuit board.

[0020] A terminal device includes a circuit board, on which a USB interface, a fast - charging chip, and a control circuit are integrated. Among them, the described USB interface function protection circuit is also integrated on the circuit board; the USB interface function protection circuit is connected to the USB interface, the fast - charging chip, and the control circuit; the USB interface is connected to the fast - charging chip and the control circuit;

[0021] The fast - charging chip detects the power supply voltage input by the USB interface and outputs a second control signal of a corresponding level, and the control circuit detects the working state of the USB interface and outputs a first control signal of a corresponding level;

[0022] The USB interface function protection circuit controls the output state of the power supply voltage according to the power supply voltage, the first control signal, and the second control signal, and performs surge protection, reverse - connection protection, burn - out protection, and over - voltage protection on the USB interface.

[0023] Compared with the prior art, for the USB interface function protection circuit and the terminal device provided by the present utility model, the USB interface function protection circuit is connected to the USB interface, the fast - charging chip, and the control circuit. The USB interface function protection circuit includes a first - level protection module, a second - level protection module, and a third - level protection module; the first - level protection module is connected to the USB interface and the second - level protection module, the second - level protection module is connected to the third - level protection module and the control circuit, and the third - level protection module is connected to the fast - charging chip; the first - level protection module is used for first - level surge protection; the second - level protection module is used for second - level surge protection, burn - out protection according to the first control signal output by the control circuit, and also detects the voltage value of the power supply voltage for over - voltage protection; the third - level protection module performs reverse - connection protection according to the second control signal output by the fast - charging chip. The USB interface function protection circuit realizes surge protection, reverse - connection protection, burn - out protection, and over - voltage protection for the USB interface, and solves the problem that the existing USB interface does not have multiple protections. Brief Description of the Drawings

[0024] Figure 1 is a structural block diagram of the terminal device provided by the present utility model.

[0025] Figure 2 is a circuit diagram of the USB interface function protection circuit provided by the present utility model. Detailed Embodiments

[0026] The present utility model provides a USB interface function protection circuit and a terminal device. To make the objectives, technical solutions and advantages of the present utility model clearer and more definite, the following further describes the present utility model in detail with reference to the accompanying drawings and by way of examples. It should be understood that the specific examples described herein are only used to explain the present utility model and are not used to limit the present utility model.

[0027] Please refer to Figure 1 and Figure 2 simultaneously. The terminal device provided by the present utility model includes a circuit board, on which a USB interface, a fast charging chip 10, a control circuit 20 and a USB interface function protection circuit 30 are integrated; the USB interface function protection circuit 30 is connected to the USB interface, the fast charging chip 10 and the control circuit 20; the USB interface is connected to the fast charging chip 10 and the control circuit 20. The fast charging chip 10 detects the power supply voltage VIN+ input by the USB interface and outputs a second control signal GPIO2 of a corresponding level, and the control circuit 20 detects the working state of the USB interface and outputs a first control signal GPIO1 of a corresponding level. The USB interface function protection circuit 30 controls the output state of the power supply voltage VIN+ according to the voltage value of the power supply voltage VIN+, and the high and low levels of the first control signal GPIO1 and the second control signal GPIO2, so as to protect the USB interface against surges, reverse connection, burning and overvoltage.

[0028] Among them, the peripherals connected to the USB interface through data lines include chargers and computers, and a USB flash drive can also be directly inserted. After inserting the peripheral, the power supply pin (VCC pin or VBUS pin, the pin name is related to the specific type) of the USB interface is connected to the power supply pin of the peripheral, the ground pin (GND pin) of the USB interface is connected to the ground pin of the peripheral, and the data pins of the USB interface are connected to the data pins of the peripheral. The fast charging chip 10 detects whether the power supply voltage VIN+ input by the USB interface is normal and outputs a second control signal GPIO2 to achieve reverse connection prevention. The control circuit 20 detects the working state of the USB interface, preferably detects whether the temperature of the USB interface is normal, and outputs the first control signal GPIO1 for burning prevention when it is too high.

[0029] The terminal device is all fast - charging mobile phones with a charge pump, or other USB devices that support detecting VBUS and controlling NMOS transistors. The circuit structures and the above - mentioned functions of the fast - charging chip 10 (preferably model SC8549, but its specific model is not limited here) and the processor are prior arts. The power supply pin of the USB interface is connected to the detection pin (VAC pin) of the fast - charging chip 10 and the corresponding detection pins of the control circuit (preferably the CPU (Central Processing Unit) or PMIC (Power Management Integrated Circuit)) to facilitate the corresponding detections by the fast - charging chip 10 and the control circuit. This embodiment mainly uses the first control signal GPIO1 output by the control circuit (provided by the GPIO pin) and the second control signal GPIO2 output by the fast - charging chip 10 (provided by the OVPGATE pin, and the pin names of other models change accordingly) to control the on - off of the output path of the power supply voltage VIN +; the specific circuit structures of the fast - charging chip 10 and the control circuit are not limited. The output end of the USB interface function protection circuit 30 is the voltage input end of the entire circuit board, which outputs the supply voltage VOUT± for power supply, and the subsequent stage can be connected to existing circuit modules and power circuits that require power supply (step - up or step - down the supply voltage VOUT± to other voltage values).

[0030] The USB interface function protection circuit 30 includes a primary protection module 31, a secondary protection module 32, and a tertiary protection module 33; the primary protection module is connected to the USB interface and the secondary protection module, the secondary protection module is connected to the tertiary protection module and the control circuit, and the tertiary protection module is connected to the fast - charging chip; the primary protection module 31 is used for primary surge protection; the secondary protection module 32 is used for secondary surge protection, anti - burning of the port according to the input first control signal GPIO1, and also detecting the voltage value of the power supply voltage VIN + for over - voltage protection; the tertiary protection module 33 performs reverse - connection protection according to the input second control signal GPIO2.

[0031] The primary protection module 31 includes a first TVS tube T1 and a diode D1; the negative electrode of the first TVS tube T1 is connected to the power supply pin of the USB interface, the negative electrode of the diode D1, and the secondary protection module 32; the positive electrode of the first TVS tube T1 is connected to the ground pin of the USB interface, the positive electrode of the diode D1, and the secondary protection module 32.

[0032] Among them, when the first TVS tube T1 is reversely broken down by a positive surge, it can absorb the surge voltage; when it is forward - conducted by a negative surge, it provides a loop for releasing the negative surge to the ground, thus playing a surge - protection function. The diode D1 is a Schottky diode.

[0033] The primary protection module 31 further includes a first capacitor C1. One end of the first capacitor C1 is connected to the negative electrode of the diode D1 and the secondary protection module 32, and the other end of the first capacitor C1 is connected to the positive electrode of the diode D2 and the secondary protection module 32. The first capacitor C1 is used to absorb the residual voltage after the first TVS tube T1 protects against surge, that is, the instantaneous surge current charges the first capacitor C1. When the first TVS tube T1 and the diode D1 conduct forwardly, the electric energy stored on the first capacitor C1 can be discharged to the ground.

[0034] The secondary protection module 32 includes a comparator U1, a first switching tube Q1, a first resistor R1, a second resistor R2, a third resistor R3, and a second capacitor C2. The inverting input terminal of the comparator U1 is connected to one end of the first resistor R1 and one end of the second resistor R2. The other end of the first resistor R1 is connected to one end of the first capacitor C1 (or the negative electrode of the diode D1), the source S of the first switching tube Q1, one end of the second capacitor C2, and the tertiary protection module 33. The other end of the second resistor R2 is connected to the ground terminal of the USB interface. The reference voltage VREF is input to the non-inverting input terminal of the comparator. The output terminal of the comparator U1 is connected to the gate G of the first switching tube Q1 and one end of the third resistor R3. The other end of the third resistor R3 inputs a first control signal GPIO1. The drain D of the first switching tube Q1 is connected to the ground terminal of the USB interface and the other end of the second capacitor C2.

[0035] Among them, the first resistor R1 and the second resistor R2 form a voltage dividing circuit, which divides the power supply voltage VIN+ input by the USB interface, outputs a divided voltage with a corresponding voltage value, and transmits it to the comparator U1 for comparison with the input reference voltage VREF, so as to realize overvoltage protection of the power supply voltage VIN+. The first switching tube Q1 is preferably a P-type MOS tube. When the comparator outputs a low level or the first control signal GPIO1 is at a low level, Q1 can be controlled to conduct, and when it is at a high level, Q1 is cut off. R3 is used to isolate the low level output by the comparator and the first control signal GPIO1.

[0036] When there is no first control signal GPIO1 input and there is a negative surge, the body diode inside Q1 conducts forwardly, and the source S and the drain D of Q1 are conducted. The second capacitor C2 is used to absorb the residual voltage after Q1 protects against surge.

[0037] The reference voltage VREF is provided by an existing power supply module, and its specific voltage value is related to overvoltage. For example, when the overvoltage protection voltage (that is, the maximum VBUS voltage at which normal operation can be carried out) is 12V, if the voltage value of the reference voltage VREF needs to be 3V, the resistance value of the first resistor R1 is preferably 30KΩ, and the resistance value of the second resistor R2 is preferably 10KΩ.

[0038] Preferably, the secondary protection module 32 further includes a second TVS tube T2. The positive electrode of the second TVS tube T2 is connected to the output terminal of the comparator and the gate of the first switching tube Q1, and the negative electrode of the second TVS tube T2 is connected to the other end of the first resistor R1 and the source S of the first switching tube Q1. The second TVS tube T2 is used to protect Q1 and prevent damage to Q1 caused by excessive power supply voltage VIN+. C2 is used to filter out interference on the gate of Q1 and prevent Q1 from being mis-triggered.

[0039] Preferably, the secondary protection module 32 further includes a fourth resistor R4, and the fourth resistor R4 is connected in parallel with the second TVS tube T2. R4 is used for current limiting to further protect Q1.

[0040] Preferably, the secondary protection module 32 further includes a third capacitor C3. One end of the third capacitor C3 is connected to the gate G of the first switching tube Q1 and the positive electrode of the second TVS tube T2, and the other end of the third capacitor C3 is connected to the source S of the first switching tube Q1 and the negative electrode of the second TVS tube T2. The third capacitor C3 is used to filter out interference on the gate of Q1 and prevent Q1 from being mis-triggered.

[0041] The tertiary protection module 33 includes a second switching tube Q2 and a third switching tube Q3. The drain D of the second switching tube Q2 is connected to the source S of the first switching tube Q1, the source S of the second switching tube Q2 is connected to the source S of the third switching tube Q3, and the gate G of the second switching tube Q2 is connected to the gate G of the third switching tube Q3 and inputs a second control signal GPIO2; the drain D of the third switching tube Q3 is the voltage input terminal.

[0042] Among them, the second switching tube Q2 and the third switching tube Q3 are preferably N-type MOS tubes. When the second control signal GPIO2 is at a high level, Q2 and Q3 are turned on, and when it is at a low level, Q2 and Q3 are turned off.

[0043] Preferably, the tertiary protection module 33 further includes a fourth capacitor C4. One end of the fourth capacitor C4 is connected to the drain D of the third switching tube Q3, and the other end of the fourth capacitor C4 is connected to the drain D of the first switching tube Q1 and the ground on the circuit board. The fourth capacitor C4 is used to filter the output supply voltage VOUT+ to make its power supply more stable.

[0044] In this embodiment, the working principle of the USB interface function protection circuit 10 to achieve the surge protection function is as follows:

[0045] When a positive surge occurs, the first TVS tube T1 at the front end is reversely broken down to absorb the surge. At this time, the voltage division value of the first resistor R1 and the second resistor R2 is greater than the reference voltage VREF, and the comparator U1 outputs a low level to turn on the first switching tube Q1, providing a low-impedance loop for the remaining surge (i.e., the Q1 conduction grounding loop), and the input power supply voltage is turned off through the short-circuit protection of Q1 grounding. At the same time, after the fast charging chip 10 detects overvoltage of the power supply voltage, it outputs a high-level second control signal GPIO2, disconnects the second switching tube Q2 and the third switching tube Q3. At this time, no power supply voltage is output, which can protect the subsequent circuit.

[0046] When a negative surge occurs, the first TVS tube T1 and the diode D1 at the front end are used for the first-stage surge protection. T1 and D1 conduct forward, providing a release loop for the negative surge. The first capacitor C1 absorbs the residual voltage of the first-stage surge protection. The first switching tube Q1 is used for the second-stage surge protection. Its body diode conducts forward, providing a release loop for the residual negative surge. The current flows from the source S of Q1 to the drain D, and then flows back to the surge source through the power supply pin of the USB interface. The second capacitor C2 is used to absorb the residual voltage after the second-stage surge protection.

[0047] The working principle of the USB interface function protection circuit 10 to achieve the reverse connection prevention function is as follows: When the USB interface is normally connected to a USB device (such as a charger or a PC (personal computer), etc.), the fast charging chip (ChargerPump) detects that the power supply voltage VIN+ on the power supply pin of the USB interface is normal (normal within the voltage range of 3.5 to 12V, and the specific value depends on the battery and the charging scheme), and outputs a high-level second control signal GPIO2 to turn on Q2 and Q3. The power supply voltage VIN+ on the power supply pin of the USB interface is output as the supply voltage VOUT+ through Q2 and Q3 to achieve charging.

[0048] When the device inserted into the USB interface is connected reversely, the fast charging chip detects that the power supply voltage VIN+ on the power supply pin of the USB interface is abnormal (the detected voltage is negative at this time, exceeding the normal voltage range), and outputs a low-level second control signal GPIO2 to control Q2 and Q3 to cut off. And because the body diode directions of the two MOS tubes Q2 and Q3 are opposite and will not conduct, the reverse connection prevention function is achieved.

[0049] The working principle of the USB interface function protection circuit 10 to achieve the anti-burning function of the port is as follows: During the charging process, when the control circuit 20 detects that the temperature of the USB interface is too high, it outputs a high-level first control signal GPIO1 to control the first switching tube Q1 to conduct through the fourth resistor R4, triggering the charging short-circuit protection, the power supply voltage VIN+ stops outputting, and the charging is turned off to prevent the USB interface from being burned out.

[0050] It should be understood that the temperature detection function of the USB interface is a prior art. For example, on a circuit board, an NTC resistor is set near the USB interface, and the control circuit 20 can obtain the corresponding temperature value by collecting the voltage value on the NTC resistor. If the voltage value is within the normal range, the temperature is normal; if it exceeds the normal range, the temperature is too high.

[0051] The working principle of the overvoltage protection function implemented by the USB interface function protection circuit 10 is as follows: when the power supply voltage on the power supply pin of the USB interface is greater than the upper limit threshold, the voltage division value of the first resistor R1 and the second resistor R2 is greater than the reference voltage VREF, and the comparator U1 outputs a low level to control Q1 to conduct, short-circuiting the positive and negative poles of the power supply at the input end, and the power supply voltage VIN+ stops output, achieving overvoltage protection. By setting the resistance values of R1 and R2 and the voltage value of the power supply voltage VIN+, the protection voltage against overvoltage and surge can be set, and the setting method is more flexible and variable, meeting the interface requirements of different devices and having a wider application range.

[0052] In specific implementation, it can also be combined with other detection functions in the terminal device to trigger short-circuit protection by controlling the conduction of the first switching tube Q1, so as to achieve the protection function of other state detections; including but not limited to the following protection functions:

[0053] Timed charging, stopping charging after the preset charging time, that is, when the control circuit 20 detects that the internally set preset charging time is reached, it controls Q1 to conduct and stop charging; or according to the set charging start and stop times, it controls Q1 to conduct and cut off correspondingly to achieve alternating charging or stopping charging.

[0054] Charging at a specific voltage, when the control circuit 20 detects that the change in the power supply voltage VIN+ on the power supply pin of the USB interface exceeds the set voltage value range, it controls Q1 to conduct and stop charging.

[0055] Charging at a specific temperature, the same as the anti-burning port function, and adding that when the detected temperature is lower than the normal range, it controls Q1 to conduct and stop charging.

[0056] Charging or stopping charging in a specific light environment, the control circuit 20 detects the intensity of the ambient light and charges or stops charging at the set intensity.

[0057] Charging or stopping charging in a user-defined setting scenario, the user defines the content of the setting scenario by himself, and when the control circuit 20 detects that the user uses certain setting scenarios, it controls charging or stopping charging.

[0058] In summary, the USB interface function protection circuit and the terminal device of the present utility model use a comparator, voltage dividing resistors, P-type and N-type MOS transistors, Schottky diodes and capacitors to form a multi-functional protection circuit under the condition of supporting high-power charging: the circuit structure is simple, with fewer components used, saving costs while also being compatible with protection functions such as surge protection, reverse connection prevention, burn-proof port protection and overvoltage protection.

[0059] It should be understood that the application of the present utility model is not limited to the above examples. For those of ordinary skill in the art, improvements or transformations can be made according to the above description, and all such improvements and transformations should fall within the protection scope of the appended claims of the present utility model.

Claims

1. A USB interface function protection circuit, connecting a USB interface, a fast charging chip and a control circuit, characterized in that: It includes a primary protection module, a secondary protection module and a tertiary protection module; the primary protection module is connected to the USB interface and the secondary protection module, the secondary protection module is connected to the tertiary protection module and the control circuit, and the tertiary protection module is connected to the fast charging chip; The primary protection module is used for primary surge protection; The secondary protection module is used to perform secondary surge protection, perform burn protection according to the first control signal output by the control circuit, and detect the voltage value of the power supply voltage to perform overvoltage protection; The third-level protection module performs anti-reverse connection protection according to the second control signal output by the fast charging chip.

2. The USB interface function protection circuit according to claim 1, characterized in that: The primary protection module includes a first TVS tube and a diode; the cathode of the first TVS tube is connected to the power pin of the USB interface, the cathode of the diode and the secondary protection module; the anode of the first TVS tube is connected to the ground pin of the USB interface, the anode of the diode and the secondary protection module.

3. The USB interface function protection circuit according to claim 2, characterized in that: The primary protection module also includes a first capacitor, one end of which is connected to the cathode of the diode and the secondary protection module, and the other end of which is connected to the anode of the diode and the secondary protection module.

4. The USB interface function protection circuit according to claim 3, characterized in that: The secondary protection module includes a comparator, a first switch tube, a first resistor, a second resistor, a third resistor and a second capacitor; The inverting input end of the comparator is connected to one end of the first resistor and one end of the second resistor; the other end of the first resistor is connected to one end of the first capacitor, the source of the first switch tube, one end of the second capacitor and the three-level protection module; The other end of the second resistor is connected to the ground pin of the USB interface, the reference voltage is input to the non-inverting input end of the comparator, the output end of the comparator is connected to the gate of the first switch tube and one end of the third resistor, the other end of the third resistor inputs the first control signal, and the drain of the first switch tube is connected to the ground pin of the USB interface and the other end of the second capacitor.

5. The USB interface function protection circuit according to claim 4, characterized in that: The secondary protection module also includes a second TVS tube, the positive electrode of the second TVS tube is connected to the output end of the comparator and the gate of the first switch tube, and the negative electrode of the second TVS tube is connected to the other end of the first resistor and the source of the first switch tube.

6. The USB interface function protection circuit according to claim 5, characterized in that: The secondary protection module further includes a fourth resistor, and the fourth resistor is connected in parallel with the second TVS tube.

7. The USB interface function protection circuit according to claim 5, characterized in that: The secondary protection module also includes a third capacitor, one end of which is connected to the gate of the first switch tube and the positive electrode of the second TVS tube, and the other end of the third capacitor is connected to the source of the first switch tube and the negative electrode of the second TVS tube.

8. The USB interface function protection circuit according to claim 4, characterized in that: The three-level protection module includes a second switch tube and a third switch tube, the drain of the second switch tube is connected to the source of the first switch tube, the source of the second switch tube is connected to the source of the third switch tube, the gate of the second switch tube is connected to the gate of the third switch tube and inputs a second control signal; the drain of the third switch tube is a voltage input terminal.

9. The USB interface function protection circuit according to claim 8, characterized in that: The three-level protection module also includes a fourth capacitor, one end of which is connected to the drain of the third switch tube, and the other end of which is connected to the drain of the first switch tube and the ground on the circuit board.

10. A terminal device, comprising a circuit board, on which a USB interface, a fast charging chip and a control circuit are integrated, characterized in that: The circuit board also integrates the USB interface function protection circuit as described in any one of claims 1 to 9; the USB interface function protection circuit is connected to the USB interface, the fast charging chip and the control circuit; the USB interface is connected to the fast charging chip and the control circuit; The fast charging chip detects the power supply voltage input by the USB interface and outputs a second control signal of a corresponding level, and the control circuit detects the working state of the USB interface and outputs a first control signal of a corresponding level; The USB interface function protection circuit controls the output state of the power supply voltage according to the power supply voltage, the first control signal and the second control signal, and performs surge protection, reverse connection protection, burnout protection and overvoltage protection on the USB interface.

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