Buck switch-mode power converter large signal transient response optimizer
A switch mode power supply (SMPS) response to a disturbance is improved by using a hysteretic control in combination with a fixed frequency, pulse-width modulated (PWM) controller for providing robust control and optimizing the response to disturbances in buck or buck derived switch mode power supply (SMPS) system topologies.
1. A switch mode power supply (SMPS) controller using hysteretic control in combination with pulse-width modulation (PWM) control, said controller comprising:
a hysteretic control circuit having a first input coupled to a reference voltage, a second input coupled to a feedback voltage representing a load side output voltage of a switch mode power supply (SMPS), a first output for controlling a high side hysteretic demand, and a second output for controlling a low side hysteretic disable;
a PWM error generator having a third input coupled to the reference voltage, a fourth input coupled to the feedback voltage, a fifth input coupled to a current sense circuit, and a third output for controlling PWM demand; and
a power circuit driver having a high side (HS) power control output, and a low side (LS) power control output, the HS and LS power control outputs are adapted to drive power switches of a switch mode power supply (SMPS), the third output of the PWM error generator is coupled to the power circuit driver for control thereof, and the first and second outputs of the hysteretic control circuit are coupled to the power circuit driver for further control thereof;
the PWM error generator third output controls the power circuit driver to make the feedback voltage substantially equal to the reference voltage unless a difference between the feedback voltage and the reference voltage is greater than at least a predetermined value, wherein if the feedback voltage is greater than the reference voltage by at least the predetermined hysteretic value, then the hysteretic control circuit forces the HS and LS power control outputs to an off-state,
if the feedback voltage is less than the reference voltage by at least the predetermined hysteretic value, then the hysteretic control circuit turns on the HS power control output and turns off the LS power control output, and
otherwise the PWM error generator controls the HS and LS power control outputs so as to force the difference between the reference voltage and the feedback voltage to substantially zero over a certain time period.
2. The SMPS controller according to claim 1 , wherein when the difference between the reference voltage and the feedback voltage is substantially zero, the PWM error generator controls the HS and LS power control outputs based upon current values received at the fifth input of the PWM error generator.
3. The SMPS controller according to claim 1 , wherein the power switches of the SMPS are power field effect transistors.
4. The SMPS controller according to claim 1 , wherein the current sense circuit comprises:
a current-to-voltage converter having a input coupled to a current sensor located on a power source side of the SMPS; and
a voltage output coupled to the fifth input of the PWM error generator.
5. The SMPS controller according to claim 1 , wherein the hysteretic control circuit comprises first and second hysteretic comparators.
6. The SMPS controller according to claim 1 , wherein the PWM error generator comprises:
an operational amplifier having a first input coupled to the reference voltage, a second input and an output representing the difference between the reference voltage and a voltage on the second input;
a compensation network having an input coupled to the feedback voltage and an output coupled to the second input of the operational amplifier, wherein the output of the operational amplifier represents the difference between the reference voltage and the compensated feedback voltage from the compensation network; and
a hysteretic comparator having a first input coupled to the output of the voltage comparator, a second input coupled to the current sense circuit through a summing node, and an output coupled to a PWM generator that is coupled to the power circuit driver, wherein the summing node adds a perturbation signal to a signal from the current sense circuit.
7. A method for controlling a switch mode power supply (SMPS) using hysteretic control in combination with pulse-width modulation (PWM) control, said method comprising the steps of:
determining a voltage difference between a reference voltage and a feedback voltage with a hysteretic control circuit and a PWM error generator, the feedback voltage being representative of an output voltage of a switch mode power supply (SMPS);
controlling high side (HS) and low side (LS) power switches of the SMPS with the PWM error generator when the voltage difference within a predetermined hysteretic window, and
if the voltage difference is outside said predetermined window and greater than the reference voltage then turning off the HS and LS drive signal, and
if the voltage difference is outside said predetermined window and smaller than the reference voltage then turning on the HS drive signal and turning off the LS drive signal.
8. The method according to claim 7 , wherein the predetermined hysteretic window is determined by two hysteretic comparators.
9. The method according to claim 7 , further comprising the step of controlling the power switches of the SMPS with the PWM error generator based upon input current when the voltage difference is substantially zero.
10. The method according to claim 9 , wherein the input current is determined by a current-to-voltage converter.