Composite loop compensation for low drop-out regulator

• US 6,703,816 B2
• Filed: 07/08/2002
• Issued: 03/09/2004
• Est. Priority Date: 03/25/2002
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Zhang, Haoran, Botker, Thomas L., Biagi, Hubert J.
• Primary Examiner(s): Riley, Shawn
• Application Number:
  US10/190,931
• Publication Number:
  US 20030178980A1
• Time in Patent Office: 610 Days
• Field of Search: 323/280, 323/281, 323/274, 323/275, 323/277, 327/465, 327/553, 327/554, 327/555
• US Class Current: 323/280
• CPC Class Codes: G05F 1/575 characterised by the feedback circuit

Abstract

A composite loop compensation circuit and method for a low drop-out regulator configured to facilitate stable operation at very low output load currents is provided. An exemplary low drop-out regulator includes an error amplifier, a pass device, and a composite loop compensation circuit. The compensation loop compensation circuit includes a plurality of segmented sense devices, a plurality of switches and a biasing component. The plurality of segmented sense devices are configured to sense an output load current, i.e., the current from the output terminal of the pass device. The plurality of switches are coupled between the plurality of segmented sense devices and a biasing component. Composite loop compensation circuit is configured to adjust the dominant first pole of the composite feedback loop based on the output load current through biasing of the active resistor component. As a result, the low drop-out regulator can include a very large pass device form addressing high currents and can remain stable for extremely low currents.

Claims

1. A low drop-out regulator for providing an output voltage to a load device, said low drop-out regulator comprising:

a pass device comprising a power transistor having an output terminal configured for providing the output voltage to the load device;

an error amplifier having an output terminal providing a current configured for driving said pass device, said error amplifier having a capacitor device configured between said output terminal and an inverting input terminal of said error amplifier;

an active resistor configured between said output terminal of said pass device and said inverting input terminal of said error amplifier to provide a composite loop; and

a composite loop compensation circuit comprising;

at least one segmented sense device configured for sensing an output load current delivered by said pass device;

a least one switch coupled to said at least one segmented sense device; and

a biasing component coupled between said at least one switch and said active resistor, said biasing component being configured for biasing said active resistor to adjust a dominant first pole created by said active resistor and said capacitor device based on said output load current delivered by said pass device.

2. The low drop-out regulator according to claim 1, wherein said composite loop compensation circuit further comprises at least one current source corresponding to said at least one segmented sense device, said at least one current source being configured to supply current to said at least one segmented sense device.

3. The low drop-out regulator according to claim 2, wherein said composite loop compensation circuit comprises a plurality of segmented sense devices, a plurality of switches, and a plurality of current sources, said plurality of current sources corresponding to said plurality of segmented sense devices and being configured to supply current to said plurality of segmented sense devices.

4. The low drop-out regulator according to claim 3, wherein each of said plurality of segmented sense devices comprises a sense transistor having a source coupled to an upper supply rail, a control terminal coupled to a control terminal of said pass device, and an output terminal coupled to one of said plurality of current sources.

5. The low drop-out regulator according to claim 3, wherein plurality of current sources comprise active current sources to increase an effective range of compensation for a range of said output load current.

6. The low drop-out regulator according to claim 3, wherein said plurality of segmented sense devices and said plurality of current sources are scaled to compensate various ranges of output current.

7. The low drop-out regulator according to claim 6, wherein said segmented sense devices are increasingly scaled in one of an octave and a decade scale.

8. The low drop-out regulator according to claim 7, wherein said plurality of current sources are scaled in a manner inversely proportional to said segmented sense devices.

9. The low drop-out regulator according to claim 1, wherein said low drop-out regulator further comprises a current feedback amplifier coupled to an output terminal of said error amplifier and configured to provide said output current for driving said control terminal of said pass device.

10. The low drop-out regulator according to claim 3, wherein said composite loop compensation circuit further comprises a second plurality of current sources configured to receive a bias voltage signal and to supply current to each of said plurality of switches to facilitate operation of said biasing component.

11. The low drop-out regulator according to claim 10, wherein said biasing component is configured with an upper and lower biasing limit to provide an upper and lower resistance value for said active resistor through selection of a number of said second plurality of current sources and said plurality of switches.

12. The low drop-out regulator according to claim 10, wherein said composite loop compensation circuit further comprises a limiting current source coupled to said biasing component, said limiting current source configured to provide at least a minimum amount of current to said biasing component.

13. A composite loop compensation circuit for compensation of an output stage having a pass device, said composite loop compensation circuit comprising:

at least one segmented sense device configured for sensing an output current delivered to the pass device, said at least one segmented sense device having a control terminal configured for coupling to a control terminal of the pass device;

a least one switch having a control terminal coupled to an output terminal of said at least one segmented sense device; and

a biasing component coupled between said at least one switch and said output stage, said biasing component being configured for biasing said output stage to adjust a dominant first pole based on the output current delivered to the pass device.

14. The composite loop compensation circuit according to claim 13, wherein said composite loop compensation circuit further comprises a least one current source configured for supplying current to said at least one segmented sense device.

15. The composite loop compensation circuit according to claim 14, wherein said composite loop compensation circuit further comprises at least one other current source coupled to said at least one switch, said at least one other current source configured for supplying current to said biasing component.

16. The composite loop compensation circuit according to claim 15, wherein said composite loop compensation circuit comprises a plurality of segmented sense devices, a plurality of switches, and a plurality of first current sources, and a plurality of second current sources, said plurality of first current sources corresponding to said plurality of segmented sense devices and being configured to supply current to said plurality of segmented sense devices, said plurality of second current sources being configured to receive a bias voltage signal and to supply current to each of said plurality of switches to facilitate operation of said biasing component.

17. The composite loop compensation circuit according to claim 16, wherein said biasing component is configured with an upper and lower biasing limit to provide an upper and lower resistance value for said active resistor through selection of a number of said second plurality of current sources and said plurality of switches.

18. The composite loop compensation circuit according to claim 17, wherein said composite loop compensation circuit further comprises a limiting current source coupled to said biasing component, said limiting current source configured to provide at least a minimum amount of current to said biasing component.

19. A method for compensation of a composite loop of a low drop-out regulator, said compensation method comprising the steps of:

sensing an output current provided to a control terminal of a pass device with a first segmented sense device; and

supplying a biasing current through a biasing component to adjust an effective resistance within an active resistor component of the low drop-out regulator, thereby adjusting a dominant first pole created by the active resistor an a capacitor device.

20. The method according to claim 19, wherein said method further comprises the steps of:

sensing said output current provided to said control terminal of said pass device with a second segmented sense device, said second segmented sense device being configured to sense said output current at an increased current level, said second segmented sense device comprising a smaller transistor device than said first segmented sense device; and

compensating said low drop-out regulator through adjustment of said biasing current through turning on switches corresponding to said output current sensed by said first segmented sense device and said second segmented sense device.

21. The method according to claim 19, wherein said method further comprises the steps of:

sensing said output current provided to said control terminal of said pass device with a plurality of segmented sense devices, said plurality of segmented sense devices being configured to sense said output current at successively increasing current levels, said plurality of segmented sense devices comprising successively smaller transistor devices than said first segmented sense device; and

compensating said low drop-out regulator through adjustment of said biasing current through selectively turning on switches corresponding to said output current sensed by said plurality of segmented sense devices.

22. The method according to claim 21, wherein said step of sensing said output current provided to said control terminal of said pass device comprises sensing with said plurality of segmented sense devices coupled to a plurality of active current sources to increase an effective range of compensation for a range of said output current.

23. The method according to claim 19, wherein said step of compensating said low drop-out regulator comprises using an upper and lower biasing limit to provide an upper and lower resistance value for said active resistor component.

24. The method according to claim 19, wherein said step of compensating said low drop-out regulator comprises providing a minimum amount for said biasing current.

25. The method according to claim 23, wherein said step of compensating comprises configuring said active resistor component to be a substantially smaller fraction in device size than a biasing component.