Multi-phase DC-DC converters with open-loop PWM for transient performance enhancement
A multi-phase switching power converter includes a panic mode detector that triggers the activation of each phase in an open-loop mode of operation in which an open-loop duty cycle is used that is greater than a closed-loop duty cycle used during closed-loop operation for the active phases.
1. A multi-phase switching power converter, comprising;
a plurality of phases, each phase including a power stage and an inductor, wherein each power stage is configured to implement a duty cycle responsive to a duty cycle control signal;
a panic mode detector configured to perform an assertion of an open-loop enable signal to trigger an open-loop mode of operation for each phase in response to an output voltage being less than a voltage droop threshold;
a plurality of pulse-width modulators corresponding to the plurality of phases, each pulse-width modulator configured to generate a closed-loop PWM control signal for its corresponding phase;
an open-loop pulse width control signal generator configured to generate an open-loop control signal for each phase; and
a multiplexer configured to respond to the assertion of the open-loop enable signal by selecting for the open-loop control signal for each phase to form each phase's duty cycle control signal.
2. The multi-phase switching power converter of claim 1 , wherein the panic-mode detector is configured to perform a de-assertion of the open-loop enable signal responsive to the output voltage equaling a desired output voltage, wherein the multiplexer is further configured to respond to the de-assertion of the open-loop enable signal by selecting for the closed-loop PWM control signal for each phase to form the phase's duty cycle control signal.
3. The multi-phase switching power converter of claim 2 , wherein each pulse-width modulator is a dual-edge pulse-width modulator.
4. The multi-phase switching power converter of claim 2 , further comprising an error amplifier configured to compare the output voltage to a reference voltage to generate an error signal for each pulse-width modulator.
5. The multi-phase switching power converter of claim 4 , wherein the error amplifier includes a compensation network.
6. The multi-phase switching power converter of claim 2 , wherein the open-loop pulse width control signal generator is configured to generate the open-loop control signal for each phase to equal a power supply voltage.
7. The multi-phase switching power converter of claim 2 , wherein the open-loop pulse width control signal generator comprises a counter configured to control a pulse-width for each open-loop control signal.
8. The multi-phase switching power converter of claim 2 , wherein the open-loop pulse width control signal generator comprises a variable RC network configured to control a pulse-width for each open-loop control signal.
9. The multi-phase switching power converter of claim 2 , wherein each power stage is configured to implement a 100% duty cycle during the open-loop mode of operation.
10. The multi-phase switching power converter of claim 2 , wherein each power stage is configured to implement a 95% duty cycle during the open-loop mode of operation.
11. The multi-phase switching power converter of claim 1 , wherein the multi-phase switching power converter comprises a multi-phase buck converter.
12. The multi-phase switching power converter of claim 1 , wherein the panic mode detector is configured to activate each phase according to a phase-activation sequence.
13. The multi-phase switching power converter of claim 12 , wherein the phase-activation sequence comprises an initial activation of a clock buffer in each power stage, a subsequent activation of the open-loop pulse width control signal generator, a subsequent activation of non-overlap logic in each power stage, and a final activation of field-effect transistor power switches in each power stage.
14. A multi-phase switching power converter, comprising;
a plurality of phases, each phase including a power stage and an inductor, wherein each power stage is configured to implement a duty cycle responsive to a duty cycle control signal;
a panic mode detector configured to perform an assertion of an open-loop enable signal to trigger an open-loop mode of operation for each phase in response to a change in an output current for the multi-phase switching power converter exceeding a current change threshold;
a plurality of pulse-width modulators corresponding to the plurality of phases, each pulse-width modulator configured to generate a closed-loop PWM control signal for its corresponding phase;
an open-loop pulse width control signal generator configured to generate an open-loop control signal for each phase; and
a multiplexer configured to respond to the assertion of the open-loop enable signal by selecting for the open-loop control signal for each phase to form each phase's duty cycle control signal.
15. The multi-phase switching power converter of claim 14 , wherein the panic-mode detector is configured to perform a de-assertion of the open-loop enable signal responsive to the output current equaling a desired output current, wherein the multiplexer is further configured to respond to the de-assertion of the open-loop enable signal by selecting for the closed-loop PWM control signal for each phase to form the phase's duty cycle control signal.
16. The multi-phase switching power converter of claim 15 , wherein each pulse-width modulator is a dual-edge pulse-width modulator.
17. The multi-phase switching power converter of claim 16 , further comprising an error amplifier configured to compare an output voltage to a reference voltage to generate an error signal for each pulse-width modulator.
18. A method of open loop operation for a multi-phase buck converter, comprising:
detecting a panic condition selected from the group consisting of an output voltage falling below a voltage droop threshold and a change in an output current exceeding a current change threshold;
in response to the detection of the panic condition, activating each phase in the multi-phase buck converter to operate in an open-loop mode of operation.
19. The method of claim 18 , further comprising:
detecting that the panic condition no longer exists; and
in response to the detection of the absence of the panic condition, transitioning each phase to a closed-loop pulse-width mode of operation.
20. The method of claim 18 , wherein operating each phase in the open-loop mode of operation comprises controlling a power stage in each phase to implement a 100% duty cycle.
21. The method of claim 18 , wherein operating each phase in the open-loop mode of operation comprises controlling a power stage in each phase to implement a 95% duty cycle.