Converter digital control circuit with adaptive compensation

• US 10,181,791 B2
• Filed: 01/22/2018
• Issued: 01/15/2019
• Est. Priority Date: 04/14/2017
• Status: Active Grant

• Current Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Original Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Inventors: Kesarwani, Kapil, Tope, Mackenzie
• Primary Examiner(s): Dole, Timothy J.
• Assistant Examiner(s): Ahmad, Shahzeb K
• Application Number:
  US15/876,641
• Publication Number:
  US 20180301985A1
• Time in Patent Office: 358 Days
• CPC Class Codes: G05B 11/42 for obtaining a characteristic which is both proportional and time-dependent, e.g. P. I., P. I. D.
• CPC Class Codes: G05F 1/575 characterised by the feedback circuit
• CPC Class Codes: G05F 5/00 Systems for regulating electric variables by detecting deviations in the electric input to the system and thereby controlling a device within the system to obtain a regulated output
• CPC Class Codes: H02M 1/0003 Details of control, feedback or regulation circuits
• CPC Class Codes: H02M 1/0022 the disturbance parameters being input voltage fluctuations
• CPC Class Codes: H02M 3/157 with digital control
• CPC Class Codes: H03G 3/004 Control by varying the supply voltage
• CPC Class Codes: H03G 3/30 in amplifiers having semiconductor devices

Abstract

A control circuit for a voltage regulator includes a digital compensator having adaptive compensation to permit operation over different operating conditions. The digital compensator includes a gain parameter that is inversely proportional to the input voltage and is independent of the switching frequency. In embodiments, the voltage regulator has a crossover frequency established by at least one pole and at least one zero and the corner frequency of the converter output filter has a first fixed, predetermined relationship with respect to the switching frequency, a second fixed, predetermined relationship with respect to the crossover frequency, and a third fixed, predetermined relationship with respect to the at least one pole and at least one zero.

Claims

1. A control circuit for a voltage regulator comprising at least one switch responsive to a voltage control signal for switching at a switching frequency and an output filter having a corner frequency, the voltage regulator configured to convert an input voltage into a regulated output voltage, comprising:

a divider coupled to the regulated output voltage to generate a divided voltage having a value that is a fraction of the regulated output voltage;

an ADC responsive to the divided voltage to generate a feedback control signal;

a digital compensator responsive to the feedback control signal to generate a compensator signal, wherein the digital compensator comprises a gain parameter that is inversely proportional to the input voltage and is independent of the switching frequency; and

a pulse width modulator responsive to the compensator signal to generate the voltage control signal.

2. The control circuit of claim 1, wherein the voltage regulator has a crossover frequency established by at least one pole and at least one zero and wherein the corner frequency of the output filter has a first fixed, predetermined relationship with respect to the switching frequency, a second fixed, predetermined relationship with respect to the crossover frequency, and a third fixed, predetermined relationship with respect to the at least one pole and at least one zero.

3. The control circuit of claim 1, wherein the digital compensator comprises a Proportional-Integral-Derivative (PID) controller comprising an integral register configured to store a value indicative of the input voltage.

4. The control circuit of claim 3, wherein one or more of a proportional gain, an integral gain, or a derivative gain of the PID controller is scaled by the value indicative of the input voltage.

5. The control circuit of claim 4, wherein the digital compensator is configured to generate the compensator signal during a first portion of cycles of a system clock signal and the gain of the digital compensator is scaled by the value indicative of the input voltage during a second portion of clock cycles different than the first portion of cycles of the system clock signal.

6. The control circuit of claim 1, wherein the digital compensator is further responsive to a feedforward signal indicative of a variation in the input voltage.

7. The control circuit of claim 1, wherein the voltage regulator is a DC-DC converter.

8. The control circuit of claim 7, wherein the DC-DC converter is a buck regulator.

9. A method for generating a voltage control signal for controlling a switch of a voltage regulator configured to convert an input voltage into a regulated output voltage, the switch operating at a switching frequency and the voltage regulator further comprising an output filter having a corner frequency, comprising:

generating a feedback control signal based on a voltage difference between the regulated output voltage and a reference voltage;

generating a duty cycle word with a digital compensator in response to the feedback control signal, comprising computing a compensator gain that is independent of the switching frequency; and

converting the duty cycle word into the voltage control signal with a pulse width modulator.

10. The method of claim 9, wherein the voltage regulator has a crossover frequency established by at least one pole and at least one zero, the method further comprising setting the corner frequency of the output filter to have a first fixed, predetermined relationship with respect to the switching frequency, a second, fixed predetermined relationship with respect to the crossover frequency, and a third fixed, predetermined relationship with respect to the at least one pole and at least one zero.

11. The method of claim 9, wherein generating the duty cycle word comprises providing a digital compensator with a proportional-Integral-Derivative (PID) controller.

12. The method of claim 11, wherein providing the digital compensator with a PID controller comprises providing an integral register in which a value indicative of the input voltage is stored and wherein computing the compensator gain comprises scaling one or more of a proportional gain, an integral gain, or a derivative gain of the PID controller by the value indicative of the input voltage.

13. The method of claim 9, wherein generating the duty cycle word comprises generating the duty cycle word in response to the feedback control signal and to a feedforward signal.

14. The method of claim 9, wherein generating the feedback control signal comprises:

dividing the regulated output voltage to generate a divided voltage having a value that is a fraction of the regulated output voltage;

generating an error voltage indicative of a difference between the divided voltage and the reference voltage; and

converting the error voltage into a digital signal to generate the feedback control signal.

15. A control circuit for a voltage regulator comprising at least one switch responsive to a voltage control signal for switching at a switching frequency and an output filter having a corner frequency, the voltage regulator having a crossover frequency established by at least one pole and at least one zero and configured to convert an input voltage into a regulated output voltage, comprising:

a divider coupled to the regulated output voltage to generate a divided voltage having a value that is a fraction of the regulated output voltage;

an error amplifier responsive to the divided voltage and to a reference voltage to generate an error voltage indicative of a difference between the divided voltage and the reference voltage;

an ADC responsive to the error voltage to generate a feedback control signal;

a digital compensator responsive to the feedback control signal to generate a compensator signal; and

a pulse width modulator responsive to the compensator signal to generate the voltage control signal,

wherein the corner frequency of the output filter has a first fixed, predetermined relationship with respect to the switching frequency, a second fixed, predetermined relationship with respect to the crossover frequency, and a third fixed, predetermined relationship with respect to the at least one pole and at least one zero.

16. The control circuit of claim 15, wherein the digital compensator comprises a PID controller comprising an integral register configured to store a value indicative of the input voltage.

17. The control circuit of claim 16, wherein one or more of a proportional gain, an integral gain, or a derivative gain of the PID controller is scaled by the value indicative of the input voltage.

18. A control circuit for a voltage regulator comprising at least one switch responsive to a PWM voltage control signal for switching at a switching frequency and an output filter having a corner frequency, the voltage regulator configured to convert an input voltage into a regulated output voltage, comprising:

means for dividing the input voltage to generate a divided voltage having a value that is a fraction of the input voltage;

means for generating an error signal indicative of a difference between the divided voltage and a reference voltage;

means for converting the error voltage into a digital feedback control signal;

means responsive to the digital feedback control signal and comprising a gain parameter that is inversely proportional to the input voltage and is independent of the switching frequency for generating a compensator signal indicative of a duty cycle for the switch; and

means for generating the PWM voltage control signal in response to the compensator signal.

19. The control circuit of claim 18, wherein the voltage regulator has a crossover frequency established by at least one pole and at least one zero and wherein the corner frequency of the output filter has a first fixed, predetermined relationship with respect to the switching frequency, a second fixed, predetermined relationship with respect to the crossover frequency, and a third fixed, predetermined relationship with respect to the at least one pole and at least one zero.

20. The control circuit of claim 18, wherein the compensator signal generating means comprises a PID controller comprising an integral register configured to store a value indicative of the input voltage.

21. The control circuit of claim 20, wherein one or more of a proportional gain, an integral gain, or a derivative gain of the PID controller is scaled by the value indicative of the input voltage.