Current-limiting protection circuit for low-side power tube of power management chip

Abstract

The utility model belongs to the field of integrated circuits, and relates to a current-limiting protection circuit for a low-side power tube of a power management chip, which is characterized in that an emitter of Q1 is connected with a resistor R1, and a base is respectively connected with a collector of Q1, a collector of Q3 and a base of Q2; the base of the Q3 is connected with bias voltage, and the emitter is connected with the resistor R3; the Q2 is used as an input tube of the common collector amplifier with the emitter resistor, an emitter of the Q2 is connected with the resistor R2, and a collector of the Q2 is connected with a collector of the load tube Q4, the other end of the capacitor C1, an emitter of the Q5 and a base of the Q6; the base electrode of the Q4 is connected with the BIAS1, and the emitter electrode of the Q4 is connected with the resistor R4; the base electrode of the Q5 is connected with an enable control signal, and the collector electrode is grounded; the collector of the Q6 is grounded, and the emitter is connected to the control port of the power tube to generate a control signal; the upper ends of the R3 and the R4 are connected with a power supply; the lower port of the R1 is grounded; the circuit is simple in structure, low in design complexity and small in chip area.

Description

Technical Field

[0001] The invention belongs to the field of integrated circuits, and in particular relates to a current limiting protection circuit for a low-side power tube of a power management chip. Background Art

[0002] Current limiting protection circuits are widely used in the field of integrated circuits, especially in power management chips that provide stable voltage and driving capability for subsequent circuits. When the current load is too large, or even when an output short circuit occurs, the current limiting protection circuit can immediately shut down the chip to prevent the chip from not working properly or being damaged due to excessive load current.

[0003] The current limiting protection circuit usually consists of a current sampling circuit and an output control part. When the current collected by the sampling circuit is greater than the set value, the current limiting protection circuit outputs an enable control signal to shut down the entire chip or part of the chip's functions. When the output load returns to the normal range, the enable control terminal does not work, and the chip returns to normal working state. The current sampling circuit usually consists of a resistor, which will produce a certain amount of power loss, especially in the case of high current, the power consumption will increase significantly, and for the LDO circuit, it will affect its minimum input-output voltage difference. Therefore, when designing a current limiting protection circuit, a smaller resistance value should be selected as much as possible, which can reduce the chip area and increase the chip's power density; at the same time, it can reduce the conduction loss and improve the chip's efficiency; and it can reduce the influence of the sampling resistor on the LDO's minimum input-output voltage difference.

[0004] Existing current limiting protection circuits such as Figure 2 As shown, in this circuit structure, when the sampling current of the lower power tube Q1 exceeds a certain value I1, the emitter voltage of Q1 is gradually raised, causing the current of the Q2 branch to increase, thereby pulling down the collector voltage of Q2. When the sampling current exceeds I2, the collector voltage of Q2 is pulled down to a low level close to GND, thereby controlling Q4 to turn on and generating a control signal EN to turn off the power tube. Although this current limiting protection circuit has a current limiting function, it requires an additional sampling resistor and the shutdown current accuracy is not high. The collector voltage of Q2 needs to experience a large current difference I2-I1 from a high level to a low level. Summary of the invention

[0005] In order to solve the problems existing in the above prior art, the present invention proposes a current limiting protection circuit for the low-side power tube of the power management chip, the circuit structure includes: 4 resistors R1-R4, 4 PNP tubes Q3-Q6, 2 NPN transistors Q1-Q2 and a capacitor C1;

[0006] The transistor Q1 is used as the input tube of the common base amplifier, the emitter of Q1 is connected to the resistor R1, and the base of Q1 is connected to the collector of Q1, the collector of Q3 and the base of Q2 respectively; the base of Q3 is connected to the bias voltage BISA1, and the emitter of Q3 is connected to the resistor R3; Q2 is used as the input tube of the common collector amplifier with emitter resistor, the emitter of Q2 is connected to the resistor R2, and the collector of Q2 is connected to the collector of the load tube Q4, the other end of the capacitor C1, the emitter of Q5 and the base of Q6; the base of Q4 is connected to BIAS1, and the emitter of Q4 is connected to the resistor R4; the base of Q5 is connected to the enable control signal ENN, and the collector is grounded; the collector of Q6 is grounded, and the emitter is connected to the control port of the power tube to generate the control signal EN; the upper ends of R3 and R4 are connected to the power supply VCC; the lower port of R1 is grounded GND_B.

[0007] Preferably, the current limiting protection circuit is further connected to an aluminum wire resistor, which is connected to the other end of the resistor R1, so that the aluminum wire resistor is connected in parallel with the ground terminal GND_B of the resistor R1.

[0008] Furthermore, the resistance of the aluminum wire resistor is smaller than the resistance of the resistors R1 and R2.

[0009] Preferably, the resistance values ​​of the resistors R1 and R2 are equal, and the resistance values ​​of the resistors R3 and R4 are equal.

[0010] Preferably, the PNP transistor Q3 and the PNP transistor Q4 are completely identical.

[0011] Beneficial effects of the present invention:

[0012] The invented current limiting protection circuit for the low-side power tube of the power management chip uses the existing aluminum wire to act as a sampling resistor, without adding an additional sampling resistor, and the power loss is significantly reduced; the present invention uses the aluminum wire between the low-side power tube and the actual ground as a sampling resistor, without adding an additional sampling resistor, reducing the conduction loss generated by entering the sampling resistor. The IB generated by the limited input impedance of the BJT bipolar transistor is used to self-generate the shutdown current threshold point. A structure with a collector resistor is used as the output load to improve the accuracy of the shutdown current; the circuit of the present invention has a high accuracy in shutting down the current; the circuit structure of the present invention is simple, the design complexity is low, and the chip area is small. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to make the purpose, technical solution and beneficial effects of the present invention clearer, the present invention provides the following drawings for illustration:

[0014] Figure 1 The basic principle block diagram of the current limiting protection circuit;

[0015] Figure 2 Circuit diagram of traditional current limiting protection circuit;

[0016] Figure 3 A specific circuit diagram of the current limiting protection circuit of the present invention. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] A current limiting protection circuit for the low-side power tube of a power management chip, such as Figure 1 As shown, it includes a control circuit, a sampling circuit, an LDO / DCDC circuit and a load; the control circuit inputs an enable signal to the LDO / DCDC circuit, and drives the load through the LDO / DCDC circuit; and the corresponding data of the load is collected through the sampling circuit.

[0019] A current limiting protection circuit for the low-side power tube of a power management chip, such as Figure 3 As shown, the circuit structure includes: 4 resistors R1~R4, 4 PNP tubes Q3~Q6, 2 NPN transistors Q1~Q2 and a capacitor C1; the transistor Q1 is used as the input tube of the common base amplifier, the emitter is connected to the resistor R1, the aluminum wire resistor is indirectly connected in parallel, the base and the collector are connected, and are connected to the collector of the load tube Q3 and the base of Q2; the base of Q3 is connected to the bias voltage BISA1, the mirror load current, and the emitter is connected to the resistor R3; Q2 is used as the input tube of the common collector amplifier with the emitter resistor, and the emitter is connected to the emitter resistor R2 with negative feedback, which can improve the stability of the common collector amplifier. , the collector is connected to the collector of the load tube Q4 and the other end of the capacitor C1 and the control shutdown tube Q6; the collector of Q4 is connected to BIAS1, and the emitter is connected to the resistor R4; Q5 is used as an enable control tube, the base is connected to the enable control signal ENN, and the collector is connected to the actual ground GND_A; Q6 is used as a switch control tube, the collector is connected to the actual ground GND_A, and the emitter is connected to the control port of the power tube to generate the control signal EN to shut down the low-side power tube; the upper ends of R3 and R4 are connected to the power supply VCC; the lower port GND_B of R1 is connected in parallel with a section of aluminum wire resistance, and the aluminum wire resistance refers to the resistance value generated by the aluminum wire from the low-side power tube to the ground.

[0020] In this embodiment, the working principle of the current limiting protection circuit includes: the resistance values of resistors R1 and R2 are equal and much larger than the resistance of the aluminum wire, the resistance values of resistors R3 and R4 are equal, Q1 and Q2 are exactly the same, and Q3 and Q4 are exactly the same. GND_A is the actual analog ground, while GND_B is the source terminal voltage of the low-side power transistor, which is the resistance of a section of aluminum wire connecting the low-side power transistor to the ground in parallel. When the current of the low-side transistor is 0, since Q1 and Q2 are equal and R1 and R2 are equal, IE1 = IE2. Since the base and collector of Q1 are connected,

[0021] I E3 = IE1 + 2IB1 = IE2 + 2IB1 = IE4 + 2IB1, so IE4 < IE3. The collector voltage of Q2 is pulled up to be close to VCC, and Q4 enters the saturation region. As the current passing through the aluminum wire resistance to sample the lower power transistor gradually increases, the voltage of GND_B is raised, causing the base voltage of Q1 to rise. Since the bases of Q1 and Q2 are connected, the current in the Q2 branch becomes larger, and the collector current of Q4 increases. The collector current of Q4 is still less than the collector current of Q3, so the collector voltage of Q2 remains almost unchanged. When the sampled current increases to the threshold current I, the collector current of Q4 is equal to the collector current of Q3, thereby quickly pulling down the collector voltage of Q2, thereby controlling Q6 to turn on and generating a control signal EN to turn off the low-side power transistor. When the collector current continues to increase, Q2 enters the saturation region, the collector voltage of Q2 is pulled to be close to GND_A, and the collector current of Q4 is equal to the collector current of Q3.

[0022] The present invention uses Q3, Q4, R3, and R4 to replace M1 and M2 of the traditional current limiting protection circuit. Since the BJT has a larger output impedance than the MOS, the output impedance is further increased after adding a resistor to the collector, improving the voltage gain and the accuracy of the turn-off current.

[0023] In this embodiment, the value of the threshold current I is: assuming that the DC current amplification coefficients of Q1 and Q2 are β, the resistance of the aluminum wire is RS, the gain coefficient of Q2 is gm2, and the collector current of Q3 is set as IE3. When the sampled current changes from 0 to I, the value of ΔIE4 is:

[0024]

[0025] According to the value of ΔIE4, it is obtained that:

[0026]

[0027] wherein, I E2 is the collector current flowing through Q2.

[0028] The current limiting protection circuit of the present invention is suitable for the low-side power tube of the power management chip. The aluminum wire between the low-side power tube and the actual ground is used as a sampling resistor, and no additional sampling resistor is needed, thereby reducing the conduction loss generated by entering the sampling resistor. The IB generated by the limited input impedance of the BJT bipolar transistor is used to self-generate the shutdown current threshold point. A structure with a collector resistor is used as an output load to improve the accuracy of the shutdown current. In addition, the current limiting protection circuit for the power management chip has a simple circuit structure, low design complexity and a small chip area.

[0029] The above embodiments further illustrate the purpose, technical solutions and advantages of the present invention in detail. It should be understood that the above embodiments are only preferred implementation modes of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made to the present invention within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A current limiting protection circuit for a low-side power tube of a power management chip, characterized in that: include: 4 resistors R1~R4, 4 PNP transistors Q3~Q6, 2 NPN transistors Q1~Q2 and a capacitor C1; The transistor Q1 is used as the input tube of the common base amplifier, the emitter of Q1 is connected to the resistor R1, and the base of Q1 is connected to the collector of Q1, the collector of Q3 and the base of Q2 respectively; the base of Q3 is connected to the bias voltage BISA1, and the emitter of Q3 is connected to the resistor R3; Q2 is used as the input tube of the common collector amplifier with emitter resistor, the emitter of Q2 is connected to the resistor R2, and the collector of Q2 is connected to the collector of the load tube Q4, the other end of the capacitor C1, the emitter of Q5 and the base of Q6; the base of Q4 is connected to BIAS1, and the emitter of Q4 is connected to the resistor R4; the base of Q5 is connected to the enable control signal ENN, and the collector is grounded; the collector of Q6 is grounded, and the emitter is connected to the control port of the power tube to generate the control signal EN; the upper ends of R3 and R4 are connected to the power supply VCC; the lower port of R1 is grounded GND_B.

2. A current limiting protection circuit for a low-side power tube of a power management chip according to claim 1, characterized in that: The current limiting protection circuit is also connected to an aluminum wire resistor, which is connected to the other end of the resistor R1, so that the aluminum wire resistor is connected in parallel with the ground terminal GND_B of the resistor R1.

3. A current limiting protection circuit for a low-side power tube of a power management chip according to claim 2, characterized in that: The resistance of the aluminum wire resistor is smaller than the resistance of resistors R1 and R2.

4. A current limiting protection circuit for a low-side power tube of a power management chip according to claim 1, characterized in that: The resistance values ​​of the resistors R1 and R2 are equal, and the resistance values ​​of the resistors R3 and R4 are equal.

5. A current limiting protection circuit for a low-side power tube of a power management chip according to claim 1, characterized in that: PNP tube Q3 and PNP tube Q4 are exactly the same.

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