Duty cycle dependent non-linear slope compensation for improved dynamic response
A two-stage converter including a buck converter and a DC-DC converter that receives power from the buck converter. The DC-DC converter generates an output voltage of the two-stage converter. A buck control circuit generates a drive signal for the buck converter. The drive signal is based on a first signal representing the output voltage, a second signal representing load applied to the buck converter, and a compensation signal. A characteristic of the compensation signal varies based on the drive signal.
1. A two-stage converter comprising:
a buck converter;
a DC-DC converter that receives power from the buck converter and generates an output voltage of the two-stage converter;
a buck control circuit that generates a drive signal for the buck converter;
a compensation circuit that generates a compensation signal having a non-linear characteristic based on the drive signal, and
wherein the drive signal is based on a first signal representing the output voltage, a second signal representing load applied to said buck converter, and the compensation signal.
2. A two-stage converter of claim 1 , wherein the non-linear characteristic includes a slope.
3. The two-stage converter of claim 2 , wherein the slope of the compensation signal at an end of a selected time period varies in accordance with a duration of the selected time period.
4. The two-stage converter of claim 3 , wherein said the drive signal is pulse-width-modulated (PWM).
5. The two-stage converter of claim 4 , wherein the selected time period defines a duty cycle of the drive signal.
6. The two-stage converter of claim 2 , wherein said compensation circuit defines a first generally linear signal, and the slope of the compensation signal varies in accordance with the first signal.
7. The two-stage converter of claim 6 , wherein said compensation circuit defines the non-linear characteristic of the compensation signal based on the first signal.
8. The two-stage converter of claim 1 , wherein the compensation circuit further includes
a first capacitance; and
a second capacitance,
wherein the non-linear characteristic of the compensation signal is determined based on said first and second capacitances.
9. The two-stage converter of claim 8 , wherein said first capacitance stores a first voltage, and said second capacitance receives a linear ramp current based on the first voltage.
10. The two-stage converter of claim 9 , wherein the compensation circuit includes a voltage dependent current source that receives the first voltage and generates the linear ramp current.
11. A method for operating a two-stage converter comprising
reducing a first voltage to a second voltage;
reducing the second voltage to a load voltage; and
controlling the second voltage via a drive signal based on a first signal representing the load voltage, a second signal representing load applied to the second voltage, and a compensation signal, wherein the compensation signal has a non-linear characteristic based on the drive signal.
12. The method of claim 11 , wherein the non-linear characteristic includes a slope.
13. The method of claim 12 , wherein the slope the compensation signal at an end of a selected time period varies in accordance with a duration of the selected time period.
14. The method of claim 13 , wherein said the drive signal is pulse-width-modulated (PWM).
15. The method of claim 14 , wherein the selected time period defines a duty cycle of the drive signal.
16. The method of claim 12 , further comprising generating the compensation signal based on a first generally linear signal, and wherein the slope of the compensation signal varies in accordance with the first signal.
17. A two-stage converter comprising:
buck converter means for reducing an input voltage to a second voltage;
DC-DC converter means for receiving power from the buck converter means and generating an output voltage of the two-stage converter; and
compensation circuit means for generating a compensation signal,
buck control means for controlling the second voltage via a drive signal based on a first signal representing the output voltage, a second signal representing load applied to the buck converter means, and the compensation signal, wherein the compensation signal has a non-linear characteristic based on the drive signal.
18. The two-stage converter of claim 17 , wherein the non-linear characteristic includes a slope.
19. The two-stage converter claim 18 , wherein the slope at an end of a selected time period varies in accordance with a duration of the selected time period.
20. The two-stage converter claim 19 , wherein said the drive signal is pulse-width-modulated (PWM).
21. The two-stage converter of claim 20 , wherein the selected time period defines a duty cycle of the drive signal.
22. The two-stage converter of claim 18 , wherein said compensation circuit means defines a first generally linear signal, and the slope of the compensation signal varying in accordance with the first signal.
23. The two-stage converter of claim 17 , wherein the compensation circuit means further including
a first capacitive means; and
a second capacitive means,
wherein the non-linear characteristic of the compensation signal is determined based on said first and second capacitive means.
24. The two-stage converter of claim 23 , wherein said first capacitive means stores a first voltage, and said second capacitive means receives a linear ramp current based on the first voltage.
25. The two-stage converter of claim 24 , wherein the compensation circuit means includes a voltage dependent current source that receives the first voltage and generates the linear ramp current.