Adaptive PWM pulse positioning for fast transient response

1. An adaptive pulse positioning system for a voltage converter providing an output voltage, said adaptive pulse positioning circuit comprising:

an adjustable ramp generator having an adjust input and providing a periodic ramp voltage having a magnitude which is adjusted based on said adjust input;

a pulse generator circuit which receives said ramp voltage and which generates a pulse signal comprising a plurality of pulses for controlling the output voltage of the voltage controller based on said ramp voltage; and

a sense and adjust circuit which senses a signal indicative of an output load transient of the voltage converter and which provides an adjust signal to said adjust input of said adjustable ramp generator to adaptively shift said pulse signal in time in response to said output load transient without adding pulses to said plurality of pulses.

2. The adaptive pulse positioning system of claim 1 , wherein said adjustable ramp generator comprises a triangle ramp generator providing a triangle ramp voltage which ramps between lower and upper threshold voltages, and wherein said adjust input adjusts said upper threshold voltage.

3. The adaptive pulse positioning system of claim 2 , wherein said sense and adjust circuit has a reset input coupled to said adjustable ramp generator and wherein said sense and adjust circuit adjusts said upper threshold for only one cycle of said ramp voltage.

4. The adaptive pulse positioning system of claim 1 , wherein said pulse generator circuit comprises:

a comparator which compares an error voltage with said ramp voltage and which generates a pulse control signal indicative thereof, and

a pulse timing circuit having a first input receiving said pulse control signal, a second input receiving a clock signal based on said ramp voltage, and an output providing said pulse signal, wherein said pulse timing circuit ensures that said pulse signal has only one pulse for each cycle of said ramp voltage.

5. The adaptive pulse positioning system of claim 1 , wherein said sense and adjust circuit comprises:

a sensor which senses an output load signal and which provides a sense voltage proportional to said output load signal;

a load transient circuit having an input receiving said sense voltage and an output providing a load transient sense voltage indicative of transients of said output load signal;

a comparator circuit which compares said load transient sense voltage with a positive threshold voltage and a negative threshold voltage, wherein said comparator circuit provides a first control signal if said load transient sense voltage reaches said positive threshold voltage and which provides a second control signal if said load transient sense voltage reaches said negative threshold voltage; and

an adjust signal generation circuit which provides said adjust signal to decrease said magnitude of said ramp voltage when said first control signal is provided and which provides said adjust signal to increase said magnitude of said ramp voltage when said second control signal is provided.

6. The adaptive pulse positioning system of claim 5 , wherein said sensor comprises a current sensor which senses output load current of the voltage converter.

7. The adaptive pulse positioning system of claim 5 , wherein said load transient circuit comprises:

a low-pass filter having an input receiving said sense voltage and having an output; and

an amplifier having a first input receiving said sense voltage, a second input coupled to said output of said low-pass filter, and an output providing said load transient sense voltage.

8. The adaptive pulse positioning system of claim 5 , wherein said adjustable ramp generator comprises a triangle ramp generator providing a triangle ramp voltage which ramps between lower and upper threshold voltages, and wherein said adjust signal decreases said upper threshold voltage when said first control signal is provided and increases said upper threshold voltage when said second control signal is provided.

9. The adaptive pulse positioning system of claim 8 , wherein said adjust signal generation circuit asserts said adjust signal proportional to said sense voltage when said first control signal is provided and asserts said adjust signal at an offset level which is adjusted by an amount proportional to said sense voltage when said second control signal is provided.

10. A method of adaptively positioning pulse width modulation pulses that are used to control an output voltage of a voltage regulator, comprising:

generating a periodic ramp voltage;

comparing the ramp voltage to an error voltage to provide a plurality of pulses in consecutive cycles of the ramp voltage;

sensing a signal indicative of a load transient of an output load of the voltage regulator; and

adjusting the ramp voltage in response to the load transient to adaptively shift the plurality of pulses in time without adding pulses.

11. The method of claim 10 , wherein said sensing a signal indicative of a load transient of an output load of the voltage regulator comprises sensing output load current.

12. The method of claim 10 , wherein said generating a ramp voltage comprises generating a ramp voltage which ranges between first and second threshold voltages, and wherein said adjusting the ramp voltage comprises adjusting at least one of the first and second threshold voltages for at least one cycle of the ramp voltage.

13. The method of claim 10 , wherein said generating a ramp voltage comprises generating a triangle ramp voltage which ramps between a lower threshold voltage and an upper threshold voltage, and wherein said adjusting the ramp voltage comprises adjusting the upper threshold voltage for at least one cycle of the ramp voltage.

14. The method of claim 13 , wherein said sensing a signal indicative of a load transient of an output load of the voltage regulator comprises detecting a positive load transient indicating an increased load, and wherein said adjusting the ramp voltage comprises decreasing the upper threshold voltage for at least one cycle of the ramp voltage.

15. The method of claim 13 , wherein said sensing a signal indicative of a load transient of an output load of the voltage regulator comprises detecting a negative load transient indicating a decreased load, and wherein said adjusting the ramp voltage comprises increasing the upper threshold voltage for at least one cycle of the ramp voltage.

16. The method of claim 10 , wherein said sensing a signal indicative of a load transient of an output load of the voltage regulator comprises:

sensing a change of an output signal;

comparing the change of the output signal with a threshold; and

detecting a load transient when the change of the output signal reaches the threshold.

17. The method of claim 10 , wherein said sensing a signal indicative of a load transient of an output load of the voltage regulator comprises:

sensing a change of an output signal;

comparing the change of the output signal with a positive threshold and a negative threshold; and

detecting a load transient when the change of the output signal reaches either one of the positive and negative thresholds.

18. The method of claim 10 , wherein said adjusting the ramp voltage comprises adjusting the ramp voltage for only one cycle.

19. The method of claim 10 , wherein said adjusting the ramp voltage comprises adjusting the ramp voltage based on relative amount of the load transient.

20. The method of claim 10 , wherein:

said generating a periodic ramp voltage comprises generating the ramp voltage between a lower threshold voltage and an upper threshold voltage; and

wherein said adjusting the ramp voltage comprises:

decreasing the upper threshold voltage by an amount proportional to the load transient indicating an increased load; and

increasing the upper threshold voltage by an offset minus an amount proportional to the load transient indicating a decreased load.