Cot control-based step-down converter control circuit and switching power supply chip

Abstract

The application discloses a control circuit of a step-down converter based on COT control and a switching power supply chip, and relates to the technical field of power supply. The control circuit comprises a first voltage comparator, an input end of which is connected with a reference signal and a feedback signal, and an output end of which is connected with an input end of a PWM comparator; a second voltage comparator, an input end of which is connected with an output signal of the step-down converter and an input signal of the step-down converter, and an output end of which is connected with a control end of the PWM comparator; and the PWM comparator, which comprises a first comparison unit, a tail current shunt unit, a control end and an output end, and outputs a control signal from the output end; when the control end inputs a first signal, the tail current shunt unit does not work, and the tail current of the first comparison unit is I1+I2; when the control end inputs a second signal, the tail current shunt unit works, and the tail current of the first comparison unit is I1. The application can take into account the output precision and stability of the system in the case that the duty cycle is large or small.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power supply control, and particularly relates to a control circuit of a COT control-based step-down converter and a switching power supply chip. BACKGROUND

[0002] In a COT control-based step-down converter (BUCK), a control signal of an output control switch tube is output by using the prior art as shown in the figure, a sampling voltage FB is obtained at an output end, the sampling voltage FB is compared with a reference voltage VREF, an EAOUT is output, the EAOUT is compared with the FB through a PWM comparator, a control signal CLK is generated, the switch of the switch tube is controlled, and the output voltage is adjusted. The EAOUT is controlled in a small fluctuation range by a clamping circuit. Figure 1

[0003] However, in the case of a large duty cycle, that is, when the voltage amplitude of the output signal of the step-down converter is relatively close to the voltage amplitude of the input signal, the working period is prolonged due to system regulation, and in particular in a high-voltage BUCK converter, the period is prolonged to tens of us, resulting in a large voltage amplitude of the EAOUT in a working period, and when compared with the feedback signal FB, a multi-pulse phenomenon occurs, thereby affecting the stability of the result. SUMMARY

[0004] The application aims to solve the problem of poor system stability of the COT control-based step-down converter in the prior art when the duty cycle is large, and provides a control circuit of a COT control-based step-down converter and a switching power supply chip.

[0005] The technical scheme is as follows:A control circuit of a COT control-based step-down converter, comprising:

[0006] a first voltage comparator, a first input end of which is connected with a reference signal, a second input end of which is connected with a feedback signal, and an output end of which is connected with an input end of a PWM comparator;

[0007] a second voltage comparator, a first input end of which is connected with an output signal of the step-down converter, a second input end of which is connected with an input signal of the step-down converter, and an output end of which is connected with a control end of the PWM comparator;

[0008] a PWM comparator, comprising a first comparison unit, a tail current shunt unit, a control end and an output end, the output end outputs a control signal, two input ends of the first comparison unit are respectively connected with the output end of the first voltage comparator and the feedback signal; when the control end inputs a first signal, the tail current shunt unit does not work, and the tail current of the first comparison unit is I1+I2; when the control end inputs a second signal, the tail current shunt unit works, and the tail current of the first comparison unit is I1.

[0009] Further, the tail current shunt unit comprises a second comparison unit, two inputs of the second comparison unit are connected with a reference signal and a feedback signal respectively, the second comparison unit works when a second signal is inputted to the control end, and a tail current of the second comparison unit is I2.

[0010] Further, the PWM comparator further comprises a first switch tube and a second switch tube, the tail current I2 is connected with the first comparison unit through the first switch tube, and the tail current I2 is connected with the second comparison unit through the second switch tube, the first switch tube and the second switch tube are controlled by the control end signal, the first switch tube is closed and the second switch tube is turned off when a first signal is inputted to the control end, and the first switch tube is turned off and the second switch tube is closed when a second signal is inputted to the control end.

[0011] Further, the output signal voltage of the buck converter is Vout, the input signal voltage of the buck converter is Vin, the second voltage comparator outputs the first signal when Vout < k*Vin, 0.5 < k < 1, otherwise the second voltage comparator outputs the second signal.

[0012] Further, the PWM comparator further comprises two RC units, the control end of the first switch tube and the control end of the second switch tube are connected with at least one RC unit respectively.

[0013] Further, the PWM comparator further comprises two RC units, the control end of the first switch tube and the control end of the second switch tube are connected with at least one RC unit respectively.

[0014] A switching power supply chip, comprising the above buck converter control circuit based on COT control.

[0015] Compared with the prior art, the buck converter control circuit based on COT control and the switching power supply chip provided by the application have the following beneficial effects:

[0016] When the system duty cycle is large, that is, the output signal of the buck converter is close to the input signal, the effective amplitude of the EAOUT signal is reduced, thereby ensuring the stability of the system; when the system duty cycle is small, the working state is equivalent to the traditional scheme, thereby ensuring the output precision. Therefore, whether the duty cycle is large or small, the output precision and stability of the system can be considered. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 It is a schematic diagram of the buck converter control circuit of the prior art;

[0018] Figure 2 It is a schematic diagram of the buck converter control circuit based on COT control in the embodiment;

[0019] Figure 3The internal schematic diagram of the PWM comparator in the embodiment. DETAILED DESCRIPTION

[0020] The application will be further explained in connection with the accompanying drawings and specific embodiments.

[0021] A COT control based step-down converter control circuit, as shown in Figure 2 , comprises:

[0022] A first voltage comparator, the first input end of which is connected with a reference signal VREF, the second input end of which is connected with a feedback signal FB, and the output end of which is connected with the input end of the PWM comparator;

[0023] A clamping circuit CLAMP, which is connected with the output end of the first voltage comparator and is used for clamping EAOUT in a smaller fluctuation range;

[0024] A second voltage comparator, the first input end of which is connected with the output signal VOUT of the step-down converter, the second input end of which is connected with the input signal VIN of the step-down converter, and the output end L_DUTY of which is connected with the control end of the PWM comparator and is used for indicating a large duty cycle;

[0025] As shown in Figure 3 , the PWM comparator (the VRIPPLE and VRAMP related contents are omitted in the figure) comprises a first comparison unit, a tail current shunt unit, a control end and an output end, the output end outputs a control signal CLK to control the opening and closing of a switch tube, two input ends of the first comparison unit are respectively connected with the output end EAOUT of the first voltage comparator and the feedback signal FB; when the control end inputs a first signal, the tail current shunt unit does not work, and the tail current of the first comparison unit is I1+I2; when the control end inputs a second signal, the tail current shunt unit works, and the tail current of the first comparison unit is I1.

[0026] In the embodiment, the tail current shunt unit comprises a second comparison unit, two input ends of the second comparison unit are respectively connected with a reference signal VREF and a feedback signal FB, the second comparison unit works when the control end inputs the second signal, and the tail current of the second comparison unit is I2. The tail current shunt unit can also be shunted in other ways, which is not limited to the comparison unit.

[0027] Specifically, in the embodiment, the control of the tail current shunt of the first comparison unit is realized by a pair of switch tubes M1 and M2 (such as MOS tubes), as shown in Figure 3As shown, the PWM comparator further comprises a first switch M1 and a second switch M2, the tail current I2 is connected to the first comparison unit through the first switch M1, and the tail current I2 is connected to the second comparison unit through the second switch M2, the first switch M1 and the second switch M2 are controlled by the control end signal, when the control end inputs the first signal (L_DUTY is low), the first switch M1 is closed, and the second switch M2 is turned off, at this time, the tail currents I1 and I2 all flow into the first comparison unit; when the control end inputs the second signal (L_DUTY is high), the first switch M1 is turned off, and the second switch M2 is closed, at this time, the tail current I1 flows into the first comparison unit, and the tail current I2 flows into the second comparison unit.

[0028] The output signal voltage of the buck converter is Vout, the input signal voltage of the buck converter is Vin, when Vout < k*Vin, 0.5 < k < 1, the value of k can be selected according to actual needs, for example, k is taken as 0.8, when the duty cycle is less than 0.8, the second voltage comparator outputs the first signal, for example, L_DUTY is low in the embodiment; otherwise, the second voltage comparator outputs the second signal, for example, L_DUTY is high in the embodiment.

[0029] The PWM comparator further comprises two RC units, the control ends of the first switch M1 and the second switch M2 are connected to at least one RC unit, for slowly and smoothly controlling the switching actions of the first switch M1 and the second switch M2. According to design needs, a plurality of inverters can be arranged to realize the control effect that the switching states of the two switches are opposite.

[0030] Overall, the PWM comparator comprises two input pairs, the negative ends of the input pairs are connected to the feedback signal FB, and the positive ends of the input pairs are connected to EAOUT and VREF respectively. When the duty cycle is small, that is, VOUT is much smaller than VIN, L_DUTY indicates low, the first switch M1 is turned on, and the second switch M2 is turned off. The tail currents I1 and I2 all flow into the input pair of the first comparison unit, at this time, the working state is equivalent to the conventional scheme. That is, in the small duty cycle, FB is directly compared with EAOUT, the control loop is controlled, and the output precision is ensured. When the duty cycle is large, L_DUTY indicates high, the signal after RC slowly turns off the first switch M1 and slowly turns on the second switch M2. Finally, the tail current ratio of the first comparison unit and the second comparison unit is I1:I2. Thus, the effective amplitude of EAOUT is reduced to I1 / (I1+I2) times within one working period. According to the need to control the ratio of I1:I2, the stability of the large duty cycle can be ensured on the premise of ensuring the output precision.

[0031] A switching power supply chip comprises the above-mentioned buck converter control circuit based on COT control, and the output precision and stability of the system can be considered regardless of whether the duty cycle is large or small.

Claims

1. A control circuit for a COT controlled buck converter, characterized by, The application relates to a COT control based step-down converter control circuit. The first voltage comparator is connected with a reference signal at the first input end and a feedback signal at the second input end, and the output end is connected with the input end of the PWM comparator. The PWM comparator comprises a first comparison unit, a tail current shunt unit, a control end and an output end, and the output end outputs a control signal; the two input ends of the first comparison unit are connected with the output end of the first voltage comparator and the feedback signal respectively; when the control end inputs a first signal, the tail current shunt unit does not work, and the tail current of the first comparison unit is I1+I2; when the control end inputs a second signal, the tail current shunt unit works, and the tail current of the first comparison unit is I1. The tail current shunt unit comprises a second comparison unit, the two input ends of the second comparison unit are connected with the reference signal and the feedback signal respectively, the second comparison unit works when the control end inputs the second signal, and the tail current of the second comparison unit is I2.

2. The COT control based buck converter control circuit of claim 1, wherein, The PWM comparator further comprises a first switch tube and a second switch tube, the tail current I2 is connected with the first comparison unit through the first switch tube, and the tail current I2 is connected with the second comparison unit through the second switch tube, the first switch tube and the second switch tube are controlled by the control end signal, the first switch tube is closed and the second switch tube is turned off when the control end inputs the first signal; the first switch tube is turned off and the second switch tube is closed when the control end inputs the second signal.

3. The COT control based buck converter control circuit of claim 2, wherein, The output signal voltage of the step-down converter is Vout, the input signal voltage of the step-down converter is Vin, the second voltage comparator outputs the first signal when Vout 4. The COT control based buck converter control circuit of any of claims 1-3, wherein, The PWM comparator further comprises two RC units, and the control ends of the first switch tube and the second switch tube are connected with at least one RC unit respectively.

5. The COT control based buck converter control circuit of any of claims 1-3, wherein, The application further comprises a clamping circuit connected with the output end of the first voltage comparator.

6. The COT control based buck converter control circuit of any of claims 1-3, wherein, The application relates to a COT control based step-down converter control circuit.

7. A switching power supply chip, characterized by comprising: The application relates to a COT control based step-down converter control circuit.

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