Buck DC-DC converter with dual feedback control

• US 8,593,125 B1
• Filed: 10/22/2012
• Issued: 11/26/2013
• Est. Priority Date: 10/22/2012
• Status: Active Grant

• Current Assignee: Microchip Technology Incorporated
• Original Assignee: Micrel Incorporated (Microchip Technology Incorporated)
• Inventors: Xue, Dashun
• Primary Examiner(s): Berhane, Adolf
• Assistant Examiner(s): NASH, GARY A
• Application Number:
  US13/657,674
• Time in Patent Office: 400 Days
• Field of Search: 323273-275, 323/280, 323282-285
• US Class Current: 323/284
• CPC Class Codes: H02M 1/15 using active elements
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators
• CPC Class Codes: H02M 3/1566 with means for compensating against rapid load changes, e.g. with auxiliary current source, with dual mode control or with inductance variation

Abstract

A buck switching regulator includes a feedback control circuit including a first gain circuit configured to generate a first feedback signal indicative of the regulated output voltage; a ripple generation circuit configured to generate a ripple signal using the switching output voltage and to inject the ripple signal to the first feedback signal; a second gain circuit configured to generate a second feedback signal indicative of the regulated output voltage; an operational transconductance amplifier (OTA) configured to generate an output signal having a magnitude indicative the difference between the second feedback signal and the first reference signal; and a comparator configured to generate a comparator output signal having an output level indicative of the difference between the output signal of the OTA and the first feedback signal. As thus configured, the buck switching regulator generates an output voltage with increased accuracy and fast transient response.

Claims

1. A buck switching regulator being configured to receiving an input voltage and to generate a regulated output voltage, the buck switching regulator controlling a high-side switch and a low-side switch based on a feedback control scheme to drive a switch output node for generating a switching output voltage, the switch output node being coupled to an LC filter to generate the regulated output voltage having a substantially constant magnitude on an output node, the buck switching regulator including a feedback control circuit comprising:

a first gain circuit configured to generate a first feedback signal indicative of the regulated output voltage;

a ripple generation circuit configured to generate a ripple signal using the switching output voltage and to inject the ripple signal to the first feedback signal;

a second gain circuit configured to generate a second feedback signal indicative of the regulated output voltage;

an operational transconductance amplifier (OTA) configured to receive the second feedback signal and a first reference signal and to generate an output signal having a magnitude indicative the difference between the second feedback signal and the first reference signal; and

a comparator configured to receive the output signal of the OTA and the first feedback signal and to generate a comparator output signal having an output level indicative of the difference between the output signal of the OTA and the first feedback signal,

wherein the first gain circuit comprises a voltage divider having a first divider ratio and the second gain circuit comprises a voltage divider having a second divider ratio, the first divider ratio being the same as or different from the second divider ratio.

2. The buck switching regulator of claim 1, wherein the output signal of the OTA is a slowly varying signal, the feedback control circuit regulating valleys of the ripple signal to be at or above the output signal of the OTA.

3. The buck switching regulator of claim 1, wherein the second feedback signal is a DC signal and the output signal of the OTA is a slowly varying DC signal.

4. The buck switching regulator of claim 1, wherein the first feedback signal has the same magnitude or a different magnitude than the second feedback signal.

5. The buck switching regulator of claim 1, further comprising:

a controller and driver circuit configured to drive the high-side switch and the low-side switch in response to the comparator output signal, the comparator output signal being asserted to turn on the high-side switch.

6. The buck switching regulator of claim 5, wherein the comparator output signal is asserted when the first feedback signal is less than the output signal of the OTA, the output signal of the OTA being a slowly varying signal.

7. The buck switching regulator of claim 5, wherein the controller and driver circuit implements a constant on-time feedback control scheme.

8. A method in buck switching regulator receiving an input voltage and controlling a high-side switch and a low-side switch using a feedback control scheme to drive a switch output node for generating a switching output voltage, the switch output node being coupled to an LC filter circuit to generate a regulated output voltage having a substantially constant magnitude on an output node, the method comprising:

generating a first feedback signal indicative of the regulated output voltage;

generating a ripple signal using the switching output voltage;

injecting the ripple signal to the first feedback signal;

generating a second feedback signal indicative of the regulated output voltage;

generating using an operational transconductance amplifier (OTA) an output signal having a magnitude indicative the difference between the second feedback signal and a first reference signal; and

generating using a comparator a comparator output signal having an output level indicative of the difference between the output signal of the OTA and the first feedback signal,

wherein generating a first feedback signal indicative of the regulated output voltage comprises dividing the regulated output voltage by a first divider ratio to generate the first feedback signal; and

generating a second feedback signal indicative of the regulated output voltage comprises dividing the regulated output voltage by a second divider ratio to generate the second feedback signal, the first divider ratio being the same as or different from the second divider ratio.

9. The method of claim 8, wherein the output signal of the OTA comprises a slowly varying signal and the method further comprises:

regulating the valleys of the ripple signal to be at or above the output signal of the OTA.

10. The method of claim 8, wherein the second feedback signal is a DC signal and the output signal of the OTA is a slowly varying DC signal.

11. The method of claim 8, wherein the first feedback signal has the same magnitude or a different magnitude than the second feedback signal.

12. The method of claim 8, further comprising:

driving the high-side switch and the low-side switch in response to the comparator output signal, the comparator output signal being asserted to turn on the high-side switch.

13. The method of claim 12, wherein generating using a comparator a comparator output signal having an output level indicative of the difference between the output signal of the OTA and the first feedback signal comprises:

asserting the comparator output signal when the first feedback signal is less than the output signal of the OTA, the output signal of the OTA being a slowly varying signal.

14. The method of claim 12, wherein driving the high-side switch and the low-side switch in response to the comparator output signal comprises:

driving the high-side switch and the low-side switch in response to the comparator output signal under a constant on-time feedback control scheme.