A fast transient response micro power module

Abstract

The present invention discloses a fast transient response micro power module, which includes an output sampling circuit, a transient detection circuit and a fixed on-time generation circuit; the output sampling circuit collects the output voltage, eliminates the error between the steady-state output voltage and the reference value through a high-bandwidth operational amplifier, and uses the sampled inductor current ripple to replace the output voltage ripple for control, so that a small ESR ceramic capacitor is selected for the output capacitor to improve the output ripple; the transient detection circuit is used to detect the situation of rapid load increase and improve the transient response speed by forcibly turning on the main power transistor; the fixed on-time generation circuit receives a control signal to generate the control signal required by the driver circuit; the present invention provides a fast transient response micro power module that can avoid the problems of the PWM control mode and solve the defect of large COT ripple at the same time.

Description

Technical Field

[0001] The present invention relates to the field of power supplies, and more specifically, to a fast transient response micro power module. Background Art

[0002] With the rapid development of microprocessors such as CPUs and FPGAs, their performance has been rapidly improved, and higher performance requirements have been put forward for the micro power modules that supply power to such microprocessors. The closed-loop control system of the micro power module is one of the important research directions. The control system affects the output steady-state characteristics of the power module and the transient response speed when the load jumps. By improving the control system, the transient response can be improved and the output ripple can be reduced.

[0003] At present, the micro power module often adopts a buck topology to convert the bus voltage into the input voltage required by the load. The system control methods often adopt types such as pulse width modulation (PWM) control and constant on-time control (COT).

[0004] PWM control is a fixed-frequency control, which adjusts the output by adjusting the on-time period by period. The output is often stabilized by an error operational amplifier or a transconductance operational amplifier, and a compensation network is required to improve the system stability, which increases the system design difficulty and complexity. The COT control method can effectively avoid the defects of the PWM control mode. It directly compares the feedback voltage with the reference value. When the feedback value is lower than the reference value, the upper switch is turned on, and after conducting for a fixed duration through a timing circuit, it is turned off until the feedback value is lower than the reference value again. Therefore, the COT control is a control method based on turning on at the bottom of the output voltage ripple. This control method has high requirements for the amplitude of the output voltage ripple and requires a large output voltage ripple to enhance the system stability. However, for the application of powering a microprocessor with a usually supply voltage of only 1V, a large output ripple cannot be tolerated. And because the on-time period is constant under the COT control method and is limited by the minimum off-time period set by the system, the transient response is poor in the case of a severe load jump. Therefore, there is an urgent need for a power module that can avoid the problems of the PWM control mode while solving the defect of large COT ripple and improving the transient response. Summary of the Invention

[0005] The present invention overcomes the deficiencies of the prior art and provides a fast transient response micro power module that can avoid the problems of the PWM control mode while solving the defect of large COT ripple.

[0006] The technical solution of the present invention is as follows:

[0007] A fast transient response micro power module includes an output sampling circuit, a transient detection circuit, and a constant on-time generation circuit;

[0008] The output sampling circuit collects the output voltage and eliminates the error between the steady-state output voltage and the reference value through a high-bandwidth operational amplifier. The inductor current ripple is sampled instead of the output voltage ripple for control, so that the output capacitor can be selected as a small ESR ceramic capacitor to improve the output ripple.

[0009] The transient detection circuit is used to detect the rapid increase of load and improve the transient response speed by forcibly turning on the main power tube;

[0010] The fixed on-time generation circuit receives the control signal and generates a control signal required by the driver circuit.

[0011] Furthermore, the output sampling circuit includes a resistor, an inductor, a capacitor, an operational amplifier and a comparator; one end of the inductor L is connected to the resistor R s One end of the inductor L is connected to the capacitor C s One end of the capacitor C out One end of the resistor R FBT Connect one end of the resistor R s The other end of the capacitor C s The other end of the capacitor C out The other end of the resistor R FBB One end of the resistor R FBB The other end of the resistor R FBT The other end of the connection;

[0012] Capacitor C s One end of the resistor R3 is connected to the capacitor C s The other end of the resistor R3 is connected to one end of the resistor R4 and the negative electrode of the remote amplifier U2. The other end of the resistor R4 and the output end of the remote amplifier U2 serve as an external pin and are connected to one end of the comparator U3.

[0013] Resistor R FBT The other end is connected to one end of the resistor R5 and one end of the operational amplifier U5, and the other end of the operational amplifier U5 is connected to the reference voltage V ref The other end of the resistor R5 is connected to one end of the capacitor C1, and the other end of the capacitor C1 and the output end of the operational amplifier U5 serve as external pins, and are connected to the other end of the comparator U3, and the output end of the comparator U3 serves as another external pin.

[0014] Further, the transient detection circuit includes a resistor, an operational amplifier, and a comparator;

[0015] One end of the resistor R9 is connected to the output end of the remote amplifier U2. 10 One end of the bias voltage Vbias1 Connect, the other end of resistor R9, and the other end of resistor R 10 are connected together to one end of operational amplifier U 12 ; one input terminal of operational amplifier U 12 is connected to one end of resistor R 11 , and one end of resistor R 12 ; the other end of resistor R 11 is grounded, and the other end of resistor R 12 is connected to the output terminal of operational amplifier U 12 together and connected to the input terminal of comparator U 14 ;

[0016] One end of resistor R 13 is connected to the output terminal of operational amplifier U5, and one end of resistor R 14 is connected to bias voltage V bias2 ; the other end of resistor R 13 , and the other end of resistor R 14 are connected together to one end of operational amplifier U 13 ; the other input terminal of operational amplifier U 13 is connected to one end of resistor R 15 , and one end of resistor R 16 ; the other end of resistor R 15 is grounded, and the other end of resistor R 16 is connected to the output terminal of operational amplifier U 13 together and connected to the other input terminal of comparator U 14 .

[0017] The advantages of the present invention are as follows:

[0018] In this solution, the error between the output voltage feedback value and the reference value is amplified using an operational amplifier to eliminate the steady-state error caused by the conduction at the trough of the ripple voltage; the sampled inductor current ripple is used instead of the output voltage ripple, thus getting rid of the dependence on the output capacitor with large ESR; a comparator is used to detect the moment when a severe load jump occurs and force the main power transistor to continuously conduct, achieving an approximate single-cycle response and improving the transient response speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is the overall circuit architecture diagram of the present invention;

[0020] Figure 2 is the key waveform diagram of the transient response of the present invention;

[0021] Figure 3 is the output sampling circuit diagram of the present invention;

[0022] Figure 4 is the fixed conduction time generation circuit diagram of the present invention;

[0023] Figure 5 This is the transient detection circuit diagram of the present invention;

[0024] Figure 6 This is the simulation waveform diagram of the steady-state output voltage of the present invention;

[0025] Figure 7 This is the simulation waveform diagram of the load jump transient of the present invention. Detailed implementation manners

[0026] The present invention will be further described below in conjunction with the accompanying drawings and detailed implementation manners. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Those parts not described in detail in this solution can all be implemented by conventional technical means.

[0027] As Figures 1 to 7 shown, a fast transient response micro-power module includes an output sampling circuit, a transient detection circuit, and a fixed on-time generation circuit;

[0028] The output sampling circuit samples the output voltage, eliminates the error between the steady-state output voltage and the reference value through a high-bandwidth operational amplifier, and uses the sampled inductor current ripple to replace the output voltage ripple for control, so that a small ESR ceramic capacitor is selected for the output capacitor to improve the output ripple;

[0029] The transient detection circuit is used to detect the situation of rapid increase in load and improve the transient response speed by forcibly turning on the main power transistor;

[0030] The fixed on-time generation circuit receives the control signal and generates the control signal required by the driver circuit.

[0031] This solution can be applied to the control systems of converters such as BUCK, forward, half-bridge, etc. For example, Figure 1 taking the single-transistor forward topology as an example. As Figure 2 shown, this is the key waveform for improving the transient response proposed by this solution, where V comp is the error amplified signal of the output voltage after passing through the operational amplifier, V iL is the ripple voltage signal obtained by sampling and converting the inductor current, EN TRANS is the transient detection signal used to control the forced turn-on of the power transistor, PGATE is the gate drive signal of the primary power transistor in the single-transistor forward topology shown in Figure 1 , and VOUT is the output voltage signal of the single-transistor forward topology shown in Figure 1 .

[0032] An input voltage sampling circuit is provided at the input end of the converter to detect the input voltage and serve as the input signal for the fixed on-time generation circuit, so that when the input voltage changes, the system switching frequency approximately remains unchanged under steady state. A current sampling circuit is provided across the inductor to sample the inductor current ripple information and convert it into a voltage signal, which serves as the input signal for the transient detection circuit and the fixed on-time generation circuit; the output voltage is sampled through a voltage division network and compared with a reference voltage by a high-bandwidth operational amplifier to adjust the output voltage, which also serves as the input signal for the fixed on-time generation circuit and the transient detection circuit; the transient detection circuit compares the current ripple information and the output voltage information. When a situation of a sharp increase in load occurs, there is V comp > V iL , at this time the control modulator forcibly turns on the upper switch until V comp ≤V iL is detected again, and the steady-state COT control is restored, thereby achieving an approximate single-cycle transient response.

[0033] Specifically, as Figure 3 shown, the output sampling circuit includes a resistor, an inductor, a capacitor, an operational amplifier, and a comparator; one end of the inductor L is connected to one end of the resistor R s , the other end of the inductor L is connected to one end of the capacitor C s , one end of the capacitor C out , and one end of the resistor R FBT ; the other end of the resistor R s is connected to the other end of the capacitor C s ; the other end of the capacitor C out and the other end of the resistor R FBB are grounded together, and the other end of the resistor R FBB is connected to the other end of the resistor R FBT ;

[0034] One end of the capacitor C s is connected to one end of the resistor R3, the other end of the capacitor C s is connected to one end of the resistor R1, the other end of the resistor R1 is connected to one end of the resistor R2 and the positive pole of the operational amplifier U2, and the other end of the resistor R2 is grounded; the other end of the resistor R3 is connected to one end of the resistor R4 and the negative pole of the operational amplifier U2, and the other end of the resistor R4 and the output end of the operational amplifier U2 together serve as an external pin and are connected to one end of the comparator U3;

[0035] The other end of the resistor R FBT is connected to one end of the resistor R5 and one end of the operational amplifier U5, and the other end of the operational amplifier U5 is connected to the reference voltage V refOne end of the resistor R5 is connected to one end of the capacitor C1. The other end of the capacitor C1 and the output end of the operational amplifier U5 are used as an external pin and are connected to the other end of the comparator U3. The output end of the comparator U3 is used as another external pin.

[0036] The output sampling circuit includes two parts: inductor current sampling and output voltage sampling. The inductor current sampling needs to satisfy

[0037] R s ·C s = i L / R DCR

[0038] where R DCR is the DC resistance of the inductor, which converts the inductor current into the voltage across C s and connects it to the two input terminals of the operational amplifier U2. U2 converts the differential signal into an output with respect to the reference ground and connects it to the inverting input terminal of the comparator U3 and the input terminal of the voltage bias U 12 ; The output voltage is connected to the inverting input terminal of the operational amplifier U5 through the voltage dividing network composed of R FBT , R FBB . The other input terminal is connected to the reference voltage. The output terminal of the operational amplifier U5 is connected to the non-inverting input terminal of the comparator U3 and the input terminal of the voltage bias U 13 ;

[0039] As Figure 4 shown, the fixed conduction time generation circuit is within the dashed box. The input voltage sampling converts the input voltage into a current signal through the resistor R7 and connects it to the anode of the diode of the optocoupler U1 to feed back to the secondary side. The sampling signal obtained at the CE terminal of the optocoupler U1 is connected to the fixed conduction time generation circuit to achieve that the steady-state switching frequency f s follows the fixed conduction duration T on to change. By adjusting the fixed conduction duration in the steady state, the steady-state switching frequency f s is approximately kept constant. The switching frequency f s follows the following formula:

[0040]

[0041] The switch S1 is controlled by the inverted output terminal of the RS flip-flop U9, charges the capacitor C3 and is connected to the non-inverting input terminal of the comparator U7, compares with the set voltage reference at the inverting input terminal to obtain the fixed conduction time, and is connected to the input terminal of the AND logic gate U8. The output terminal of U8 is connected to the R terminal of the RS flip-flop U9; The current source I1 charges the capacitor C2 through the switch S2 controlled by the non-inverted output terminal of the RS flip-flop U9 and is connected to the non-inverting input terminal of the comparator U 10 and compares with the set voltage reference at the inverting input terminal of the comparator to obtain the minimum turn-off time, and is connected to the AND logic gate U11 The input terminal of 11 is connected to the output of operational amplifier U3, and the output of the logic gate is connected to the S terminal of RS flip-flop U9. After receiving the input, the output of RS flip-flop U9 is connected to the drive circuit to control the switching power transistor, and the in-phase output terminal is connected to the input terminal of logic gate U8.

[0042] As Figure 5 shown, the transient detection circuit includes a resistor, an operational amplifier, and a comparator;

[0043] One end of resistor R9 is connected to the output terminal of operational amplifier U2, and one end of resistor R 10 is connected to the bias voltage V bias1 The other end of resistor R9 and the other end of resistor R 10 are connected together to one end of operational amplifier U 12 The other input terminal of operational amplifier U 12 is connected to one end of resistor R 11 and one end of resistor R 12 The other end of resistor R 11 is grounded, and the other end of resistor R 12 is connected to the output terminal of operational amplifier U 12 together to connect to the input terminal of comparator U 14 ;

[0044] One end of resistor R 13 is connected to the output terminal of operational amplifier U5, and one end of resistor R 14 is connected to the bias voltage V bias2 The other end of resistor R 13 and the other end of resistor R 14 are connected together to one end of operational amplifier U 13 The other input terminal of operational amplifier U 13 is connected to one end of resistor R 15 and one end of resistor R 16 The other end of resistor R 15 is grounded, and the other end of resistor R 16 is connected to the output terminal of operational amplifier U 13 together to connect to the other input terminal of comparator U 14 ;

[0045] Combined with Figure 2 , in the time period from t0 to t1, the load condition remains unchanged, the circuit is in the steady-state COT control, and it is in the fixed-time conduction stage. During this stage, the inductor current rises. At the moment of t1, when the fixed conduction time is reached, both U7 and U8 output high levels, the output of RS flip-flop U9 is cleared, and the primary switching transistor is turned off;

[0046] During the time period from t1 to t3, the primary switch is turned off, the inductor current decreases, and the current source I1 charges the capacitor C2. At time t2, the minimum off-time limit is reached, and the comparator U 10 output goes high; at time t3, the output of the operational amplifier U2 is lower than the output of U5, that is, the sampled inductor current signal is less than the voltage error amplified signal, the output of the comparator U3 goes high, and the AND gate U 11 output goes high, the output of the RS flip-flop U9 goes high, and the primary switch is turned on again;

[0047] At time t4, the load current increases. At this time, the system is still in the steady-state COT control. The conduction time of the primary switch is fixed, and the off-time is limited by the minimum off-time;

[0048] At time t5, the comparator U 14 detects that the input of the inverting terminal is higher than the input of the non-inverting terminal, and the output terminal is pulled low. The corresponding input of the AND gate U8 is low, and no clear signal is sent, and the switch continues to conduct;

[0049] At time t6, the comparator U 14 detects that the input of the inverting terminal is lower than the input of the non-inverting terminal again, and the output is high, and the COT control is restored.

[0050] The SIMPLIS software is used to build the circuit for simulation. The simulation takes the single-switch forward topology as an example. The input voltage is 48V, a transformer with a turns ratio of 12:1 is used, the secondary inductance is 200nH, and the output capacitor selects 6 100uF capacitors with an ESR of 5mΩ in parallel. The simulation results are as Figure 6 the steady-state output voltage waveform under a load of 5A. The average value of the steady-state output voltage is 994mV, and the output value set according to the reference value and the voltage dividing network is 995mV; the output voltage ripple is only 2.66mV; when the load jumps from 5A to 40A, the change rate is 5A / us, and the transient waveform is as Figure 7 , and the maximum undershoot voltage is 47mV.

[0051] In summary, this solution can get rid of the dependence on the output capacitor with large ESR in the traditional COT control method, and there is almost no steady-state error. Compared with the COT control method, under the same other conditions, the transient response detection and control of this solution can reduce the undershoot amplitude under load jump by 70%.

[0052] The above is only the preferred implementation manner of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several improvements and retouches can still be made, and these improvements and retouches should also be regarded as within the protection scope of the present invention.

Claims

1. A fast transient response micro power module, characterized in that: It includes an output sampling circuit, a transient detection circuit, and a fixed on-time generation circuit; The output sampling circuit samples the output voltage, eliminates the error between the steady-state output voltage and the reference value through a high-bandwidth operational amplifier, and uses the sampled inductor current ripple to replace the output voltage ripple for control, enabling the selection of a small ESR ceramic capacitor for the output capacitor to improve the output ripple; The transient detection circuit is used to detect the situation of a rapid increase in the load and improves the transient response speed by forcibly turning on the main power transistor; The fixed on-time generation circuit receives three control signals to generate the control signals required by the driver circuit. The three control signals include the inductor current ripple sampling signal, the transient detection signal of a rapid increase in the load, and the input voltage sampling signal.

2. The fast transient response micro-power module according to claim 1, characterized in that: The output sampling circuit includes resistors, inductors, capacitors, operational amplifiers, and comparators; one end of the inductor L is connected to one end of the resistor Rs, and the other end of the inductor L is connected to one end of the capacitor Cs, one end of the capacitor Cout, and one end of the resistor RFBT. The other end of the resistor Rs is connected to the other end of the capacitor Cs; the other end of the capacitor Cout and one end of the resistor RFBB are grounded together, and the other end of the resistor RFBB is connected to the other end of the resistor RFBT; One end of the capacitor Cs is connected to one end of the resistor R3, and the other end of the capacitor Cs is connected to one end of the resistor R1. The other end of the resistor R1 is connected to one end of the resistor R2 and the positive terminal of the operational amplifier U2. The other end of the resistor R2 is grounded; the other end of the resistor R3 is connected to one end of the resistor R4 and the negative terminal of the operational amplifier U2. The other end of the resistor R4 and the output terminal of the operational amplifier U2 are used as an external pin and are connected to one end of the comparator U3; The other end of the resistor RFBT is connected to one end of the resistor R5 and one end of the operational amplifier U5. The other end of the operational amplifier U5 is connected to the reference voltage Vref. The other end of the resistor R5 is connected to one end of the capacitor C1. The other end of the capacitor C1 and the output terminal of the operational amplifier U5 are used as an external pin and are connected to the other end of the comparator U3. The output terminal of the comparator U3 is used as another external pin.

3. A fast transient response micro power module according to claim 2, characterized in that: The transient detection circuit includes resistors, operational amplifiers, and comparators; One end of the resistor R9 is connected to the output terminal of the operational amplifier U2. One end of the resistor R10 is connected to the bias voltage Vbias1. The other ends of the resistor R9 and the resistor R10 are connected to one end of the operational amplifier U12 together. The other input terminal of the operational amplifier U12 is connected to one end of the resistor R11 and one end of the resistor R12. The other end of the resistor R11 is grounded. The other end of the resistor R12 and the output terminal of the operational amplifier U12 are connected to the input terminal of the comparator U14 together; One end of resistor R13 is connected to the output terminal of operational amplifier U5. One end of resistor R14 is connected to bias voltage Vbias2. The other end of resistor R13 and the other end of resistor R14 are connected together to one end of operational amplifier U13. The other input terminal of operational amplifier U13 is connected to one end of resistor R15 and one end of resistor R16. The other end of resistor R15 is grounded. The other end of resistor R16 and the output terminal of operational amplifier U13 are connected together to the other input terminal of comparator U14.

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