Protection circuit of power management chip

Abstract

The utility model discloses a protection circuit of a power management chip, and the power management chip controls the on or off of a power switch tube according to an undervoltage protection signal output by an undervoltage protection circuit. The power management chip controls the charge pump module to output a stable high-voltage signal through the soft start module according to an overvoltage protection signal output by the overvoltage protection circuit so as to drive the power switch tube, and the LDO voltage division unit can enable other modules to work under low voltage through voltage division and reasonably arrange a high-voltage circuit so as to improve the circuit reliability. The under-voltage protection circuit and the overvoltage protection circuit respectively output an under-voltage protection signal and an overvoltage protection signal to the power management chip so as to control whether the power switch tube is turned on or not, so that the lithium battery is protected from being damaged by under-voltage charging and overvoltage charging, the soft start module enables a high-voltage signal output by the charge pump module to become stable, and the safety of the lithium battery is improved. The discharge module ensures appropriate power circulation of peripheral equipment output by the circuit, and the working safety and reliability of the protection circuit of the power management chip are improved.

Description

Technical Field

[0001] The utility model belongs to the technical field of integrated circuit protection, and in particular relates to a protection circuit of a power management chip. Background Art

[0002] At present, lithium batteries have advantages that other batteries cannot replace, but they also have inherent defects, which are also important factors restricting the development and application of lithium batteries. Some defects of lithium batteries can be tolerated and ignored compared with their advantages, such as the lack of interchangeability between lithium batteries and dry batteries, the inability to charge rapidly, high internal impedance, large operating voltage changes, and large discharge rates. However, some defects seriously restrict the development of lithium batteries, such as safety issues caused by overcharging. When the charging voltage of a lithium battery is overvoltage, due to the large storage capacity of the lithium battery, the battery will quickly heat up and release a large amount of heat, while generating residual battery energy. This energy decomposes the electrolyte inside the lithium battery to produce gas, resulting in the phenomenon of lithium batteries becoming bulging, smoking, and even burning or exploding. In addition, too low a charging voltage will also damage the lithium battery, deteriorate the battery's performance, and reduce the cycle life of the lithium battery. Therefore, it is necessary to provide effective protection for the power management chip of the lithium battery to ensure the safe and reliable performance of the lithium battery. Utility Model Content

[0003] In view of the above problems, the utility model provides a protection circuit for a power management chip, which has the characteristics of high precision and fast response, and can prevent the lithium battery from causing damage to itself and the external environment due to overvoltage and undervoltage, so as to solve the problems raised in the above background technology.

[0004] In order to achieve the above purpose, the utility model adopts the following technical solutions:

[0005] The utility model provides a protection circuit of a power management chip, the protection circuit of the power management chip comprises a power management chip, a power switch tube, a soft start module, a voltage protection module, a charge pump module and a discharge module, the soft start module, the voltage protection module, the charge pump module and the discharge module are connected to the power management chip, the soft start module and the charge pump module are connected to the discharge module, the drain of the power switch tube is connected to the voltage input end, the source of the power switch tube is connected to the voltage output end, and the gate of the power switch tube is connected to the soft start module;

[0006] The voltage protection module includes an undervoltage protection circuit and an overvoltage protection circuit, and the undervoltage protection circuit and the overvoltage protection circuit are connected to the power management chip;

[0007] Among them, the power management chip enables the undervoltage protection circuit and the overvoltage protection circuit to collect the voltage of the input power supply voltage, the power management chip controls the conduction or shutdown of the power switch tube according to the undervoltage protection signal output by the undervoltage protection circuit, and the discharge module is used to perform discharge protection on the voltage at the voltage output end; the power management chip controls the charge pump module to output a smooth high-voltage signal through the soft start module to drive the power switch tube according to the overvoltage protection signal output by the overvoltage protection circuit.

[0008] As a further preferred embodiment of the above technical solution, the charge pump module includes an oscillator, a transformer circuit and a charge pump connected in sequence, the oscillator is used to generate a square wave and output it to the transformer circuit, the transformer circuit changes the amplitude of the square wave and inputs it to the charge pump to complete the voltage boost.

[0009] As a further preferred embodiment of the above technical solution, when the enable signal of the power management chip, the undervoltage protection signal and the overvoltage protection signal are all at high levels, the protection circuit of the power management chip works normally;

[0010] When the input signal received by the oscillator from the power management chip is at a high level, the oscillator starts.

[0011] As a further preferred embodiment of the above technical solution, the undervoltage protection circuit and the overvoltage protection circuit both include a comparator.

[0012] As a further preferred embodiment of the above technical solution, the voltage protection module also includes an LDO voltage divider unit, the undervoltage protection circuit is connected to the LDO voltage divider unit, and the LDO voltage divider unit is used to divide the input power supply voltage of the voltage input end into a stable voltage and output it to each module in the circuit.

[0013] As a further preferred embodiment of the above technical solution, the voltage protection module also includes a reference voltage circuit connected to the LDO voltage divider unit, and the reference voltage circuit is used to provide a reference voltage to the overvoltage protection circuit, and the overvoltage protection circuit compares the collected overvoltage sampling signal with the reference voltage to output an overvoltage protection signal.

[0014] As a further preferred embodiment of the above technical solution, the protection circuit of the power management chip further includes an enabling module, the enabling module is connected to the power management chip, and the enabling module is connected to the external port Control output and the external port The enable control signal EN has the opposite level.

[0015] As a further preferred embodiment of the above technical solution, when the external port When the high-level chip is turned off or the input power supply voltage of the voltage input terminal does not reach the undervoltage threshold of the undervoltage protection circuit, and the voltage of the voltage output terminal is greater than the discharge threshold of the discharge module, the discharge module is started to quickly reduce the voltage of the voltage output terminal.

[0016] As a further preferred embodiment of the above technical solution, the enabling module is an inverter, and the input end of the inverter is connected to the external port The output end of the inverter is connected to the power management chip.

[0017] As a further preferred embodiment of the above technical solution, when the protection circuit of the power management chip works normally and the power switch tube is turned on, the difference between the input power supply voltage and the turn-on voltage of the power switch tube is greater than the voltage of the voltage output terminal.

[0018] Compared with the prior art, the beneficial effects of the utility model are:

[0019] By setting a power management chip, a power switch tube, a soft start module, a voltage protection module, a charge pump module and a discharge module, the power management chip enables the undervoltage protection circuit and the overvoltage protection circuit to collect the voltage of the input power supply voltage, the power management chip controls the conduction or shutdown of the power switch tube according to the undervoltage protection signal output by the undervoltage protection circuit, the discharge module is used to discharge the voltage at the voltage output end, the power management chip controls the charge pump module to output a stable high-voltage signal to drive the power switch tube through the soft start module according to the overvoltage protection signal output by the overvoltage protection circuit, the LDO voltage divider unit can enable other modules to work in a low-voltage environment through voltage division and reasonably arrange the high-voltage circuit to improve the reliability of the circuit, the undervoltage protection circuit and the overvoltage protection circuit respectively output the undervoltage protection signal and the overvoltage protection signal to the power management chip to control whether the power switch tube is turned on, thereby protecting the lithium battery from being damaged by undervoltage charging and overvoltage charging. The gate voltage of the power switch tube is provided by the soft drive module. The charge pump module can boost the power switch tube, making the gate voltage of the power switch tube higher than the input power supply voltage to avoid input power supply voltage loss. The soft start module makes the high voltage signal output by the charge pump module stable. The discharge module ensures the proper power circulation of the peripheral devices output by the circuit, thereby improving the working safety and reliability of the protection circuit of the power management chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a circuit schematic diagram of the protection circuit of the power management chip proposed by the utility model;

[0021] Figure 2 This is a circuit diagram of the LDO voltage divider unit proposed by the utility model;

[0022] Figure 3 The circuit diagram of the reference voltage circuit proposed by the utility model.

[0023] Figure 4 The utility model is a circuit diagram of the undervoltage protection circuit.

[0024] Figure 5 The utility model is a circuit diagram of the overvoltage protection circuit.

[0025] Figure 6 A circuit diagram of an oscillator proposed in the utility model;

[0026] Figure 7 This is a circuit diagram of the charge pump proposed by the utility model.

[0027] The main component symbols are described as follows:

[0028] 100-power management chip; 110-power switch tube; 120-soft start module; 130-charge pump module; 140-discharge module; 150-undervoltage protection circuit; 160-overvoltage protection circuit; 170-LDO voltage divider unit; 180-reference voltage circuit; 190-enable module. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments.

[0030] See also Figure 1 The utility model provides a protection circuit of a power management chip, the protection circuit of the power management chip includes a power management chip 100, a power switch tube 110, a soft start module 120, a voltage protection module, a charge pump module 130 and a discharge module 140, the soft start module 120, the voltage protection module, the charge pump module 130, the discharge module 140 are connected to the power management chip 100, the soft start module 120, the charge pump module 130 are connected to the discharge module 140, the drain of the power switch tube 110 is connected to the voltage input end, the source of the power switch tube 110 is connected to the voltage output end, and the gate of the power switch tube 110 is connected to the soft start module 120;

[0031] The voltage protection module includes an undervoltage protection circuit 150 and an overvoltage protection circuit 160, and the undervoltage protection circuit 150 and the overvoltage protection circuit 160 are connected to the power management chip 100;

[0032] Among them, the power management chip 100 enables the undervoltage protection circuit 150 and the overvoltage protection circuit 160 to collect the input power supply voltage, and the power management chip 100 controls the conduction or shutdown of the power switch tube 110 according to the undervoltage protection signal output by the undervoltage protection circuit 150, and the discharge module 140 is used to discharge the voltage at the voltage output end; the power management chip 100 controls the charge pump module 130 to output a smooth high-voltage signal to drive the power switch tube 110 through the soft start module 120 according to the overvoltage protection signal output by the overvoltage protection circuit 160.

[0033] In this embodiment, the voltage protection module further includes an LDO voltage divider unit 170, the undervoltage protection circuit 150 is connected to the LDO voltage divider unit 170, and the LDO voltage divider unit 170 is used to divide the input power supply voltage of the voltage input terminal into a stable voltage and output it to each module in the circuit. The voltage protection module also includes a reference voltage circuit 180 connected to the LDO voltage divider unit 170, and the reference voltage circuit 180 is used to provide a reference voltage to the overvoltage protection circuit 160. The overvoltage protection circuit 160 compares the collected overvoltage sampling signal with the reference voltage and outputs an overvoltage protection signal. The undervoltage protection circuit 150 and the overvoltage protection circuit 160 both include a comparator. When the protection circuit of the power management chip works normally and the power switch tube 110 is turned on, the difference between the input power supply voltage and the turn-on voltage of the power switch tube 110 is greater than the voltage of the voltage output terminal.

[0034] Among them, improving the reliability of the protection circuit of the power management chip, that is, the protection chip, requires reasonable arrangement of the high and low voltage circuits in the circuit, because the performance of high-voltage resistant devices is generally not as good as that of low-voltage devices, and they often require a larger area. Therefore, under the condition that the semiconductor devices in the protection chip are not damaged by high voltage, the use of high-voltage devices is reduced as much as possible, which can well reduce the area of ​​the lithium battery charging protection chip and save costs. For the low-voltage requirements of most modules in the chip, the LDO voltage divider unit 170 can be completed. Each part in the LDO voltage divider unit 170 divides the power supply voltage through a large proportion of high-voltage consumption, and outputs the divided voltage to each module as the power supply voltage of each module, and drives the module to work normally. Some modules work in a low-voltage environment. The charge pump module 130, the soft start module 120 and the power switch tube 110 are parts that are inevitably in contact with the high voltage. High-voltage devices need to be set in appropriate places, and undervoltage protection circuits 150 and overvoltage protection circuits 160 are set to prevent high voltage breakdown from damaging the chip.

[0035] It should be noted that the LDO voltage divider unit divides the input power supply voltage into a relatively stable voltage and outputs it to other modules as the VDD of each module. In order to meet the different needs of each module, the LDO voltage divider unit is divided into four parts and outputs four different voltages. Since the input power supply voltage can reach 28V, the LDO voltage divider unit also contains a high-voltage part, and through voltage division, other modules can work in a low-voltage environment. The reliability of the circuit is also improved by the reasonable arrangement of high-voltage circuits. Through control signals such as undervoltage protection signals and enable signals, the LDO voltage divider unit can make some circuits that generate VDD of certain modules not work, thereby shutting down these modules, making the circuit more stable and reliable, and reducing the power consumption of the chip.

[0036] See also Figure 6 and Figure 7 Optionally, the charge pump module includes an oscillator, a transformer circuit and a charge pump connected in sequence, the oscillator is used to generate a square wave and output it to the transformer circuit, the transformer circuit changes the amplitude of the square wave and inputs it to the charge pump to complete the boost.

[0037] In this embodiment, when the enable signal of the power management chip, the undervoltage protection signal and the overvoltage protection signal are all at high levels, the protection circuit of the power management chip operates normally; when the oscillator receives the input signal of the power management chip at a high level, the oscillator starts. The undervoltage protection circuit and the overvoltage protection circuit both include a comparator. The voltage protection module also includes an LDO voltage divider unit, the undervoltage protection circuit is connected to the LDO voltage divider unit, and the LDO voltage divider unit is used to divide the input power supply voltage of the voltage input end into a stable voltage and output it to each module in the circuit. The voltage protection module also includes a reference voltage circuit connected to the LDO voltage divider unit, the reference voltage circuit is used to provide a reference voltage to the overvoltage protection circuit, and the overvoltage protection circuit compares the collected overvoltage sampling signal with the reference voltage to output an overvoltage protection signal. The undervoltage protection circuit has a built-in reference comparator and does not require an external reference signal. The undervoltage signal can be used to control the reference comparator to directly determine whether the input voltage has reached the set undervoltage threshold, and output an undervoltage protection signal to the power management chip to control whether the power switch tube is turned on, thereby protecting the lithium battery from damage caused by undervoltage charging.

[0038] It should be noted that the overvoltage protection circuit compares the overvoltage sampling signal with the reference voltage provided by the reference voltage circuit through a high-speed comparator to determine whether the input power supply voltage reaches the set overvoltage threshold, and outputs an overvoltage protection signal to the power management chip to control whether the power switch tube is turned on, thereby protecting the lithium battery from being damaged by overvoltage charging. The reference voltage circuit is an indispensable module circuit in the protection circuit of the power management chip. The circuit provides a reference voltage for the overvoltage protection circuit. The accuracy of the reference voltage directly affects the accuracy of the overvoltage protection, thereby affecting whether the chip can reliably protect the lithium battery. It is an important criterion for judging the quality of the chip. The oscillator is used to generate a periodic square wave signal, which is obtained through a voltage conversion circuit to obtain the required square wave signal and output to the charge pump. The power switch tube used in the chip is an NMOS tube. The drain of the power switch tube is connected to the input power supply voltage IN, the source of the power switch tube is connected to the output voltage OUT, and the gate voltage of the power switch tube is provided by the soft start module. When the chip works normally and the power switch tube is turned on, the power supply of the soft start module in the chip and other modules are the same input power supply voltage IN, so there is no boost circuit. Then the source voltage value of the power switch tube must be less than the input voltage value, that is, the input power supply voltage has been lost and cannot pass completely. The charge pump plays a role in boosting, making the gate voltage of the power switch tube higher than the power supply voltage to avoid the above loss. The soft start module makes the signal stable according to the large fluctuation of the high voltage signal output by the charge pump module to drive the power switch tube.

[0039] It should be understood that by setting the power management chip 100, the power switch tube 110, the soft start module 120, the voltage protection module, the charge pump module 130 and the discharge module 140, the power management chip 100 enables the undervoltage protection circuit 150 and the overvoltage protection circuit 160 to collect the voltage of the input power supply voltage, the power management chip 100 controls the on or off of the power switch tube 110 according to the undervoltage protection signal output by the undervoltage protection circuit 150, the discharge module 140 is used to discharge the voltage at the voltage output end, and the power management chip 100 controls the on or off of the power switch tube 110 according to the overvoltage protection signal output by the undervoltage protection circuit 150. The overvoltage protection signal output by the protection circuit 160 controls the charge pump module 130 to output a stable high-voltage signal to drive the power switch tube 110 through the soft start module 120. The LDO voltage divider unit 170 can make other modules work in a low-voltage environment through voltage division and reasonably arrange the high-voltage circuit to improve the reliability of the circuit. The undervoltage protection circuit 150 and the overvoltage protection circuit 160 respectively output the undervoltage protection signal and the overvoltage protection signal to the power management chip 100 to control whether the power switch tube 110 is turned on, thereby protecting the lithium battery from damage by undervoltage charging and overvoltage charging. The gate voltage of the power switch tube 110 is provided by the soft drive module 120. The charge pump module 130 can boost the power switch tube 110 so that the gate voltage of the power switch tube 110 is higher than the input power supply voltage to avoid the loss of the input power supply voltage. The soft start module 120 makes the high voltage signal output by the charge pump module 130 stable. The discharge module 140 ensures the appropriate power cycle of the peripheral equipment output by the circuit, and improves the working safety and reliability of the protection circuit of the power management chip.

[0040] Specifically, see Figure 2 , the protection circuit of the power management chip can be connected to a maximum voltage of 28V, but except for the power switch tube, voltage protection module and soft start module, other modules do not have high-voltage devices and are in a low-voltage working state. This is due to the LDO voltage divider unit converting the input power supply voltage into the stable voltage required by each module. The circuit principle of the LDO voltage divider unit is roughly as follows: the high-voltage consumption HNM1_D is used for voltage division, the PMOS tubes PM1, PM2, PM3, PM4 and PM5 are used for clamping, the NMOS tube NM2 is used for feedback, and the NMOS tube NM1 connected to DN1 is used to control the gate-source voltage of HNM1_D. When VDD1 rises with the rise of VIN, the gate voltage of NMOS tube NM2 rises, and the gate-source voltage of HNM1_D drops, then the drain voltage of HNM1_D rises and VDD1 drops to achieve voltage stabilization.

[0041] The specific working process of the circuit of the LDO voltage divider unit is as follows: when the circuit is unloaded, the input power supply voltage begins to rise, initially NM2 is cut off, and the high voltage consumption HNM1_D works in the linear region. As the gate voltage of NM2 increases, NM2 eventually works in the saturation region, and the current flowing through HNM1_D is equal to the current of NM2, which is about ten nanoamperes. When the circuit is loaded, for example 20μA, the current flowing through the high voltage consumption HNM1_D is approximately equal to 20μA. When the input power supply voltage VIN starts to rise from zero, initially, the high voltage consumption HNM1_D works in the linear region. As VDD1 rises with the rise of VIN, the gate voltage of the NMOS tube NM1 rises, and the absolute value of the gate-source voltage of HNM1_D increases until it enters the saturation region. NM2 is not turned on yet and works in the subthreshold region, because the current flowing through its branch has caused the absolute value of the gate-source voltage of HNM1_D to rise to make HNM1_D enter the subthreshold region. NMOS tube NM2 controls the current of the branch where it is located, so that the gate-source voltage of HNM1_D can be controlled. When the load current is large, the absolute value of the gate-source voltage of HNM1_D required to achieve balance must be smaller, making VDD1 smaller. When the load current is small, the absolute value of the gate-source voltage of HNM1_D required to achieve balance must be larger, so that VDD1 is larger. Therefore, the stable voltage VDD1 output by the circuit will fluctuate to a certain extent due to the influence of the load, but the fluctuation range is small and can fully meet the needs of subsequent modules.

[0042] Specifically, see Figure 3, the reference voltage circuit includes a startup circuit in a dotted box and a reference circuit connected to the startup circuit, that is, the reference voltage circuit includes a zero state and a normal working state. When the reference voltage circuit does not start working, the circuit is in a zero state. The function of the startup circuit is to make the reference voltage circuit enter the working state after the reference voltage circuit is powered on. The signal fVIN indicates that the input power supply voltage VIN is obtained through a large resistor, which is approximately equal to VIN. The gates of the NMOS tubes NM1, NM2, and NM3 are respectively connected to the output signal VL1 of the LDO voltage divider unit, the reference voltage VREF, and the over-temperature protection signal VL2 of the over-temperature protection circuit (not shown in the figure). NM1 and NM3 are used to ensure that the startup circuit will work normally only when the LDO voltage divider unit and the over-temperature protection circuit are working normally. When the startup circuit starts to power on, the reference circuit has not started yet and the reference voltages VREF and VL3 are both low, and the NMOS tubes NM2 and NM5 are turned off, so the voltage at point A in the startup circuit is high, and becomes low after passing through an inverter, so that PM3 is turned on. Since the gate of PMOS tube PM3 is grounded, the branch where NM6 is located is turned on. At this time, the potential of point B in the startup circuit is high, so that NM7 is turned on, which will give a relatively low voltage to point C in the startup circuit, and the reference circuit is started. When the reference circuit, LDO voltage divider unit and over-temperature protection circuit are all working normally, NMOS tubes NM1, NM2 and NM3 are turned on, pulling the potential of point A down, which becomes high after passing through an inverter, PM3 is turned off, and PM5 is turned on at the same time, pulling the potential of point B down to ground, NM6 and NM7 are turned off, and the startup is completed. The shutdown of the startup circuit does not affect the reference circuit and the over-temperature protection circuit.

[0043] Among them, the gate signal of PMOS tube PM6 comes from the over-temperature protection circuit, and its function is similar to that of NMOS tube NM3, ensuring that the reference voltage circuit is in a closed state when the over-temperature protection circuit does not work properly. The resistors R4 and R5 are equal, and the types and sizes of PM4 and PM5 are the same, ensuring that the currents of these two branches are equal. The area ratio of transistors NPN1, NPN2, NPN3 and NPN4 is 1:1:2:1, and the base-emitter voltages of NPN1 and NPN4 are equal to play a clamping role, so that the voltages at points D and E of the reference circuit are equal. VL3 is filtered by RC to obtain the output reference voltage VREF, and the ideal reference voltage can be obtained by adjusting the resistance values ​​of resistors R1, R2 and R3.

[0044] Specifically, see Figure 4, the undervoltage protection circuit is an important part of the power management chip. When the input power supply voltage is lower than the normal working voltage of the chip, some modules of the chip may not work, or even produce unpredictable logic errors. Therefore, the chip needs to integrate the undervoltage protection circuit. When the input power supply voltage is lower than the set low-voltage threshold, some modules in the chip can be turned off to make the chip in a certain state. At the same time, the power switch tube is turned off, the charging power is cut off, and the lithium battery is protected from damage by undervoltage charging. The undervoltage protection circuit improves the reliability and safety of the chip. VDD3 is the stable voltage output by the LDO voltage divider unit, EN is the enable signal output by the enable module, and after passing through an inverter, the signal L5 is obtained, which is used to control whether the NMOS tubes NM11, NM12, NM13 and NM14 are turned on. At the same time, the enable signal controls whether the PMOS tubes PM12 and PM13 are turned on. Both PMOS and NMOS are control tubes used to ensure that the circuit is in the off state when the enable signal is low, and the undervoltage signal is at a low level. PM14, PM5, NM15 and NM16 form a bias circuit to provide a suitable bias current for the follower and output module.

[0045] Among them, PM16, PM17, NM17, NM18, NM19 and NM20 form a follower, and the gate of NMOS tube NM17 is the undervoltage sampling signal L6. When the power supply voltage IN starts to rise from zero, VDD and the undervoltage sampling signal VL6 also start to rise from zero. At this time, NM17, N / 18, PM16 and PM17 are all in the cut-off area until the VL6 voltage rises to a threshold (NM17 is turned on at this time), and NM17 starts to draw current from NM19, so that PM16 and PM17 are turned on, VL6 = VL7, and VL8 has one more turn-on voltage than VL7. As VL6 continues to increase, VL8 reaches the VDD of this module. If VL6 continues to increase, VL8 = VDD3. When the voltage drops from high to low, part of the circuit is to isolate the undervoltage sampling signal VL6 and the reference comparison part to prevent mutual influence.

[0046] When the input power supply voltage starts to rise from low, the signal VL7 follows and rises, that is, the base voltage of the two transistors rises. When it rises to a value higher than the reference voltage, the linear amplification current of the branch where the transistor NPN6 is located is smaller than the linear amplification circuit of the branch where the transistor NPN5 is located. If the PMOS tubes PM18 and PM19 that form the current mirror are equal in size, the current balance is broken, the transistor NPN5 enters the saturation state, the voltage of VL9 drops, PM20 is turned on, and VL10 rises. After being shaped by the two-stage inverter, a high-level undervoltage protection signal UVLO is output, in which the signal VL11 obtained by VL10 after passing through the first-stage inverter outputs the NMOS tube in parallel with the resistor in the undervoltage sampling circuit, which is used to achieve the hysteresis effect.

[0047] When the input power supply voltage drops from a higher level, the signal VL7 also drops, that is, the base voltage of the two transistors drops. When it drops below the reference voltage, the sizes of the PMOS tubes PM18 and PM19 that form the current mirror are equal, the current balance is broken, the PMOS tube PM19 enters the linear region, the potential of VL9 rises, and VL10 drops. After being shaped by the two-stage inverter, a low-level undervoltage protection signal UVLO is output, and the chip enters the undervoltage lockout state. The input power supply voltage at this time is the minimum power supply voltage for the normal operation of most modules of the chip.

[0048] Specifically, see Figure 5 The NMOS tubes NM22, NM23, NM24, NM25 and the PMOS tubes PM21, PM22, PM23 in the overvoltage protection circuit are control tubes. The gate voltage of the PMOS tube is the undervoltage protection signal UVLO, and the gate voltage of the NMOS tube is the inverse VL14 of the undervoltage protection signal. The control tube will ensure that the overvoltage protection circuit is turned off when the chip is in undervoltage mode, and the output overvoltage protection signal must be low, thereby ensuring the working stability of the chip. The gate voltage of NM27 and NM28 comes from the over-temperature protection circuit. When the over-temperature protection circuit does not work properly, VL17 and Vl18 are low, then this part of the circuit is closed, Z1 is a three-state gate, and when the chip is in under-voltage mode, the three-state gate is closed, that is, when the over-temperature protection circuit works normally and the under-voltage protection signal is high, the over-voltage protection circuit is normally turned on, and the current mirror composed of PM24 and PM25 and the current mirror composed of NM28, NM29, NM30, and NM21 mirror the current of the branch where NM27 is located to each branch. The circuit works normally, generates bias voltages VL15 and VL16, pulls down the gate voltage of PM26, and PM26 is turned on.

[0049] Among them, the overvoltage comparator in the overvoltage protection circuit is a three-stage differential comparator. PM26, PM27 and PM28 are PMOS tubes with gate voltages of VL15 and VL16 connected in series in the actual circuit to provide tail current for each stage. One end of the three-state gates Z2 and Z3 is connected to the first-stage differential comparator, and the other end is connected to the reference voltage VREF and the reference voltage VL12 respectively. VL13 is the overvoltage adopted voltage. When the protection circuit of the power management chip works normally, assuming that the input power supply voltage rises from low, initially after passing through the comparator, the potential of point M is low, and the potential of point N is high. At this time, the overvoltage protection signal OVLO is high. After passing through the inverter, VL19 is low, VL20 is high, the three-state gate Z2 is turned on, and Z3 is turned off. The sampling voltage is compared with the reference voltage VREF. When the sampling voltage VL2 rises to be greater than the reference voltage VREF, the comparator output flips, and the overvoltage protection signal OVLO flips to low at the same time. After passing through the inverter, VL8 is high and VL9 is low. The three-state gate Z3 is turned on and Z2 is turned off. The sampling voltage is compared with the reference voltage VL12. At this time, the chip enters the overvoltage protection mode. The overvoltage protection signal turns off the power switch tube after passing through the power management chip, and charging stops. When the input power supply voltage drops from a high level, the three-state gate Z3 is turned on and Z2 is turned off. The input end of the comparator is the reference voltage and the sampling voltage. When the sampling voltage VL13 drops to the reference voltage VREF, the comparator output does not flip. When VL13 drops to the lower level of the reference voltage VL12, the comparator output flips to low, and after passing through the inverter, the overvoltage protection signal OVLO flips to high, and the overvoltage protection mode is released. If other control signals are normal, the power switch tube is turned on and the lithium battery is charged normally. At this time, VL19 is at a high potential, VL20 is at a low potential, the three-state gate Z2 is turned on, and Z3 is closed. The sampled voltage is compared with the reference voltage VREF again. The reference voltage VL12 is smaller than the reference voltage VREF, realizing the hysteresis effect and avoiding repeated opening and closing due to input power supply voltage jitter or overshoot.

[0050] Specifically, see Figure 6 and Figure 7, the charge pump module is a boost circuit. When the chip is working properly and the power switch transistor is conducting normally, the relationship between the gate voltage VG of the power switch transistor and the output voltage VOUT is VOUT < VG - VTH, where VTH represents the turn-on voltage of the power switch transistor. The power supply of the soft start module and other modules are all the same input power supply voltage VIN. If there is no boost circuit, the gate voltage value of the power switch transistor must be less than the input voltage value, that is, VG < VIN, then VOUT < VIN - VTH. Therefore, the output voltage VOUT is at least one voltage difference VTH lower than the input power supply voltage. After passing through the voltage protection module, the input power supply voltage is stepped down, resulting in the effective range of the input voltage being limited to a relatively small range, which also limits the input voltage range of the subsequent chips or devices. This kind of loss is unacceptable for lithium battery charging protection. Therefore, a module needs to be integrated in the chip to increase the gate voltage of the power switch transistor to at least one turn-on voltage value higher than the input power supply voltage, and the charge pump module can complete the boost well.

[0051] Among them, the charge pump module mainly includes an oscillator, a transformer circuit, and a charge pump. The oscillator generates a square wave, the transformer circuit changes the amplitude of this square wave, and finally inputs it into the charge pump to complete the boost. The power supply voltage of the oscillator and the power supply voltage VDD3 of the transformer circuit and the subsequent inverter both come from the LDO voltage division unit, and the two are of different magnitudes. The signal VL21 is generated by the power management chip. When the enable signal is high, the undervoltage protection signal is high, and the overvoltage protection signal is high, that is, when the chip is working properly, the signal VL21 is high and the oscillator starts. Otherwise, the signal VL21 is low. At this time, the signal VL22 is high, VL23 is low, and the circuit continuously outputs the low-level signal VL25. When VL21 flips to high, the circuit starts. Since VL23 and VL24 are high in the initial state, VL22 flips to low and VL23 flips to high at this time. Because the voltage across the capacitor cannot jump, VL24 jumps up at this time. VL24 discharges through the resistor R8 and the NMOS transistor of the NAND gate until VL24 is low to the threshold voltage of the inverter, and the voltage flips. The signal VL22 is high and VL23 is low. At this time, because the voltage across the capacitor cannot jump, VL24 jumps down. The power supply voltage of this part charges VL24 through the PMOS transistor of the NOT gate F1 and the resistor R8 until VL24 rises to the threshold voltage of the inverter and the voltage flips. The signal VL22 is low and VL23 is high. Then continue the above process to achieve oscillation, and the oscillation period can be adjusted by resistors and capacitors.

[0052] Among them, NMOS tubes NM32, NM33 and PMOS tubes PM22, PM23 form a voltage conversion circuit, so that the amplitude of the final square wave signal VL25 is VDD3. If the signal VL23 is low, VL26 is high, so NM32 is turned on, NM33 is turned off, and PM22 pulls the potential of point P up to VDD3. Similarly, if the signal VL23 is high, VL26 is low, so NM32 is turned off, NM33 is turned on, and the NMOS tube pulls point P down to the ground, so the circuit realizes the change of the amplitude of the square wave to VDD3. The square wave signal VL25 with an amplitude of VDD3 is input to another voltage conversion circuit to obtain square wave signals VL27 and VL28 with an amplitude of VDD4 and opposite phases. VDD4 is also generated by the LDO voltage divider unit and is greater than VDD3, so that the voltage output by the charge pump is higher. Figure 7 VL29 in the figure is the input power supply voltage VIN obtained by the voltage protection module, which is almost equal to the input power supply voltage. Signals VL27 and VL28 are two square waves with an amplitude of VDD4 and opposite phases. The charge pump mainly uses the characteristic that the voltage across the capacitor cannot change suddenly. When the square wave VL27 is at a high level and VL28 is at a low level, the NMOS tube NM35 is turned on, the capacitor C2 is charged, and the PMOS tube PM24 is turned on, so that the charge charged on the capacitor C3 is released to the output end. Similarly, when the square wave VL27 is at a low level and VL28 is at a high level, NM34 is turned on, the capacitor C3 is charged, and PM25 is turned on, so that the charge charged on the capacitor C2 is released to the output end. Through this interactive charging method, VL30=VL29+VDD4 is obtained to achieve voltage boost.

[0053] Optionally, the protection circuit of the power management chip further includes an enabling module, the enabling module is connected to the power management chip, and the enabling module is connected to the power management chip by an external port. Control output and the external port The enable control signal EN has the opposite level.

[0054] In this embodiment, when the external port When the high-level chip is turned off or the input power voltage of the voltage input terminal does not reach the undervoltage threshold of the undervoltage protection circuit, and the voltage of the voltage output terminal is greater than the discharge threshold of the discharge module, which is recorded as Vpd, the discharge module is started to make the voltage of the voltage output terminal drop rapidly. The enabling module is an inverter, and the input terminal of the inverter is connected to the external port The output end of the inverter is connected to the power management chip. The protection circuit of the power management chip can be regarded as a protection chip. The protection chip has four pins, of which the GND pin is connected to the ground of each module in the chip or the ground of the system, and the external port I / O pins It is the enable control terminal. When this pin is high, the chip enters the shutdown mode, and the input and output are disconnected. When this pin is low, the chip works normally. Pin IN is connected to the input power supply VBUS, and pin OUT is connected to the protected circuit. Pin IN and pin OUT are connected by a power switch tube. The opening or disconnection of the power switch tube determines whether the charging line is open, thereby protecting the lithium battery from overvoltage or undervoltage.

[0055] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes within the technical scope disclosed by the present invention according to the technical scheme and the utility model concept of the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A protection circuit for a power management chip, characterized in that: The protection circuit of the power management chip comprises a power management chip, a power switch tube, a soft start module, a voltage protection module, a charge pump module and a discharge module, wherein the soft start module, the voltage protection module, the charge pump module and the discharge module are connected to the power management chip, the soft start module and the charge pump module are connected to the discharge module, the drain of the power switch tube is connected to the voltage input end, the source of the power switch tube is connected to the voltage output end, and the gate of the power switch tube is connected to the soft start module; The voltage protection module includes an undervoltage protection circuit and an overvoltage protection circuit, and the undervoltage protection circuit and the overvoltage protection circuit are connected to the power management chip; Among them, the power management chip enables the undervoltage protection circuit and the overvoltage protection circuit to collect the input power supply voltage, the power management chip controls the on or off of the power switch tube according to the undervoltage protection signal output by the undervoltage protection circuit, and the discharge module is used to perform discharge protection on the voltage at the voltage output end; the power management chip controls the charge pump module to output a smooth high-voltage signal through the soft start module to drive the power switch tube according to the overvoltage protection signal output by the overvoltage protection circuit.

2. The protection circuit of the power management chip according to claim 1, characterized in that: The charge pump module includes an oscillator, a voltage conversion circuit and a charge pump connected in sequence, wherein the oscillator is used to generate a square wave and output it to the voltage conversion circuit, and the voltage conversion circuit changes the amplitude of the square wave and inputs it to the charge pump to complete the voltage boost.

3. The protection circuit of the power management chip according to claim 2, characterized in that: When the enable signal of the power management chip, the undervoltage protection signal and the overvoltage protection signal are all at high levels, the protection circuit of the power management chip works normally; When the input signal received by the oscillator from the power management chip is at a high level, the oscillator starts.

4. The protection circuit of the power management chip according to claim 3, characterized in that: The undervoltage protection circuit and the overvoltage protection circuit both include a comparator.

5. The protection circuit of the power management chip according to claim 1, characterized in that: The voltage protection module also includes an LDO voltage divider unit, the undervoltage protection circuit is connected to the LDO voltage divider unit, and the LDO voltage divider unit is used to divide the input power supply voltage of the voltage input end into a stable voltage and output it to each module in the circuit.

6. The protection circuit of the power management chip according to claim 5, characterized in that: The voltage protection module also includes a reference voltage circuit connected to the LDO voltage divider unit, the reference voltage circuit is used to provide a reference voltage to the overvoltage protection circuit, and the overvoltage protection circuit compares the collected overvoltage sampling signal with the reference voltage to output an overvoltage protection signal.

7. The protection circuit of the power management chip according to claim 1, characterized in that: The protection circuit of the power management chip also includes an enabling module, which is connected to the power management chip and is connected to the power management chip by an external port. Control output and the external port The enable control signal EN has the opposite level.

8. The protection circuit of the power management chip according to claim 7, characterized in that: When the external port When the high-level chip is turned off or the input power supply voltage of the voltage input terminal does not reach the undervoltage threshold of the undervoltage protection circuit, and the voltage of the voltage output terminal is greater than the discharge threshold of the discharge module, the discharge module is started to quickly reduce the voltage of the voltage output terminal.

9. The protection circuit of the power management chip according to claim 7, characterized in that: The enabling module is an inverter, and the input end of the inverter is connected to the external port The output end of the inverter is connected to the power management chip.

10. The protection circuit of the power management chip according to claim 1, characterized in that: When the protection circuit of the power management chip works normally and the power switch tube is turned on, the difference between the input power supply voltage and the turn-on voltage of the power switch tube is greater than the voltage of the voltage output terminal.

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