Method and apparatus for dynamic voltage transition control in semi-resonant and resonant converters

1. A voltage converter, comprising:

a power stage coupled to a power source;

a passive circuit coupling the power stage to an output capacitor;

a synchronous rectification (SR) switch operable to couple the passive circuit to ground when the SR switch is conducting;

a linear controller operable to control switching of the SR switch and switch devices included in the power stage, to regulate an output voltage of the voltage converter based on a reference voltage; and

an adaptive voltage positioning (AVP) circuit operable to generate an offset voltage applied to the reference voltage based on a first signal representing output current of the voltage converter, and to subtract a second signal from the first signal, the second signal approximating a surge current applied to the output capacitor via the passive circuit for charging the output capacitor during transitions in the reference voltage.

2. The voltage converter of claim 1 , wherein the second signal has a half-cycle sinusoidal-like waveform.

3. The voltage converter of claim 1 , wherein the second signal has a triangular waveform.

4. The voltage converter of claim 1 , wherein the linear controller is operable to generate the second signal based on an expected peak of the surge current and a magnitude of change in the reference voltage.

5. The voltage converter of claim 1 , wherein the AVP circuit is operable to generate a current compensation signal based on a difference between the first signal and the second signal, filter the current compensation signal to generate the offset voltage and subtract the offset voltage and an output voltage feedback signal from the reference voltage to generate an error signal input to the linear controller.

6. The voltage converter of claim 1 , wherein the linear controller is operable to generate a duty cycle for use in switching the SR switch and the switch devices included in the power stage, wherein an offset is applied to the duty cycle or on-time generated from the duty cycle, and wherein the offset increases the duty cycle or the on-time.

7. The voltage converter of claim 6 , wherein the offset applied to the duty cycle or the on-time is fixed.

8. The voltage converter of claim 6 , wherein the linear controller is operable to accommodate a plurality of different degrees of change in the reference voltage, and wherein the offset applied to the duty cycle or the on-time depends on the degree of change in the reference voltage.

9. The voltage converter of claim 6 , wherein a rising edge of the offset applied to the duty cycle or the on-time is steeper than a falling edge of the offset.

10. The voltage converter of claim 6 , wherein the linear controller is operable to control an amplitude and timing of the offset applied to the duty cycle or the on-time based on a slew rate of the voltage converter and a magnitude of change in the reference voltage.

11. The voltage converter of claim 6 , wherein the offset applied to the duty cycle or the on-time is based on the output capacitor and a slew rate of the voltage converter.

12. The voltage converter of claim 1 , wherein during a transition in the reference voltage from a first voltage level to a second voltage level the linear controller is operable to shorten an off-time duration at a beginning of the transition and during which energy is transferred to the output capacitor via the passive circuit, so that a subsequent on-time of longer duration than the off-time occurs sooner in the transition in the reference voltage.

13. The voltage converter of claim 12 , wherein the linear controller is operable to shorten the off-time duration for a plurality of switching periods at the beginning of the transition.

14. The voltage converter of claim 1 , wherein the passive circuit is configured such that a current flowing through the SR switch when the SR switch is conducting has a shape of a half cycle of a sinusoid, and the surge current applied to the output capacitor comprises half cycle sinusoids.

15. The voltage converter of claim 1 , wherein the passive circuit comprises a tapped inductor and the SR switch is operable to couple a center tap of the tapped inductor to ground when the SR switch is conducting.

16. The voltage converter of claim 1 , wherein the power stage comprises a high-side switch and a low-side switch, and wherein the linear controller is operable to control the SR switch such that the SR switch conducts when the low-side switch is conducting, and the SR switch does not conduct when the low-side switch is not conducting.

17. A method of operating a voltage converter that includes a power stage coupled to a power source, a passive circuit coupling the power stage to an output capacitor, and a synchronous rectification (SR) switch operable to couple the passive circuit to ground when the SR switch is conducting, the method comprising:

controlling, using a linear control technique, switching of the SR switch and switch devices included in the power stage to regulate an output voltage of the voltage converter based on a reference voltage;

generating an offset voltage applied to the reference voltage based on a first signal representing output current of the voltage converter; and

subtracting a second signal from the first signal, the second signal approximating a surge current applied to the output capacitor via the passive circuit for charging the output capacitor during transitions in the reference voltage.

18. The method of claim 17 , wherein the second signal has a half-cycle sinusoidal-like waveform.

19. The method of claim 17 , wherein the second signal has a triangular waveform.

20. The method of claim 17 , further comprising:

generating the second signal based on an expected peak of the surge current and a magnitude of change in the reference voltage.

21. The method of claim 17 , further comprising:

generating a current compensation signal based on a difference between the first signal and the second signal;

filtering the current compensation signal to generate the offset voltage; and

subtracting the offset voltage and an output voltage feedback signal from the reference voltage to generate an error signal input to a linear controller of the voltage converter.

22. The method of claim 17 , further comprising:

generating a duty cycle for use in switching the SR switch and the switch devices included in the power stage; and

applying an offset to the duty cycle or on-time generated from the duty cycle, the offset increasing the duty cycle or the on-time.

23. The method of claim 22 , wherein the offset applied to the duty cycle or the on-time is fixed.

24. The method of claim 22 , further comprising:

accommodating a plurality of different degrees of change in the reference voltage,

wherein the offset applied to the duty cycle or the on-time depends on the degree of change in the reference voltage.

25. The method of claim 22 , wherein a rising edge of the offset applied to the duty cycle or the on-time is steeper than a falling edge of the offset.

26. The method of claim 22 , further comprising:

controlling an amplitude and timing of the offset applied to the duty cycle or the on-time based on a slew rate of the voltage converter and a magnitude of change in the reference voltage.

27. The method of claim 22 , wherein the offset applied to the duty cycle or the on-time is based on the output capacitor and a slew rate of the voltage converter.

28. The method of claim 17 , further comprising:

during a transition in the reference voltage from a first voltage level to a second voltage level, shortening an off-time duration at a beginning of the transition and during which energy is transferred to the output capacitor via the passive circuit, so that a subsequent on-time of longer duration than the off-time occurs sooner in the transition in the reference voltage.

29. The method of claim 28 , further comprising:

shortening the off-time duration for a plurality of switching periods at the beginning of the transition.