Output stage compensation circuit

• US 6,700,360 B2
• Filed: 03/25/2002
• Issued: 03/02/2004
• Est. Priority Date: 03/25/2002
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Burt, Rodney T., Biagi, Hubert J.
• Primary Examiner(s): Riley, Shawn
• Application Number:
  US10/107,270
• Publication Number:
  US 20030178978A1
• Time in Patent Office: 708 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

An output stage compensation circuit and method for a low drop-out regulator configured to facilitate stable operation while providing output voltage and current to downstream circuit devices is provided. An exemplary low drop-out regulator is configured with an output stage compensation circuit including one or more segmented sense devices configured to drive one or more fixed current sources. Each segmented sense device is configured to compensate a suitable range of output current and to multiply the effect of associated compensation capacitors. The one or more segmented sense devices are configured to provide pole-zero compensation based on output current. Further, the current range of each segment can be overlapped. As a result, the stability of the low drop-out regulator is not dependent upon the output current requirements or the capacitance requirements of the downstream circuit.

Claims

1. A low drop-out regulator having a compensation scheme for providing stable operation while providing output current to a downstream circuit device, said low drop-out regulator comprising:

a pass device comprising a power transistor for driving a load current to the downstream device, said pass device having a control terminal;

an error amplifier for providing an output current configured for driving said control terminal of said pass device; and

an output stage compensation circuit comprising at least one segmented sense device configured to sense said output current.

2. The low drop-out regulator according to claim 1, wherein said output stage 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 output stage compensation circuit comprises a plurality of segmented sense devices 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 gate coupled to gate of pass device, and a drain coupled to one of said plurality of current sources.

5. The low drop-out regulator according to claim 3, wherein said at least one segmented sense device comprises a compensation capacitor coupled between a control terminal and an output terminal of said at least one segmented sense device.

6. 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 current.

7. 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.

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

9. 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.

10. 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.

11. A compensation circuit for compensation of an output stage, said compensation circuit comprising:

at least one segmented sense device configured to provide pole-zero compensation, said at least one segmented sense device comprising a sense transistor having a control terminal configured for coupling to a control terminal of a pass device; and

at least one current source configured for supplying current to said at least one segmented sense device.

12. The output stage compensation circuit according to claim 11, wherein said at least one segmented sense device further comprises an input terminal configured for coupling to an upper supply rail and an output terminal coupled to said at least one current source.

13. The output stage compensation circuit according to claim 12, wherein said at least one segmented sense device further comprises a compensation capacitor coupled between said control terminal and said output terminal of said at least one segmented sense device.

14. The output stage compensation circuit according to claim 13, wherein said output stage compensation circuit further comprises a plurality of segmented sense devices having a plurality of compensation capacitors and a plurality of current sources comprising active current sources.

15. The output stage compensation circuit according to claim 14, wherein said plurality of segmented sense devices are scaled to provide facilitate compensation for overlapping ranges of output current.

16. The output stage compensation circuit according to claim 15, wherein said plurality of current sources are scaled inversely proportional in size to said plurality of segmented sense devices.

17. The output stage compensation circuit according to claim 14, wherein said plurality of segmented sense devices are configured to multiply the effects of compensation from said compensation capacitors.

18. The output stage compensation circuit according to claim 11, wherein a control terminal of said at least one current source can be actively driven by a current-mirror device of a current feedback amplifier.

19. The output stage compensation circuit according to claim 14, wherein said plurality of segmented sense devices comprise a large scaled sense device configured to provide compensation at extremely low levels of output current.

20. The output stage compensation circuit according to claim 19, wherein said plurality of segmented sense devices comprise a small scaled sense device configured with said large scaled sense device to effectively limit ground current utilized during compensation at low output currents.

21. The output stage compensation circuit according to claim 13, wherein said compensation capacitor is configured in series with a resistor, and said at least one current source is configured in series with another resistor, both of said resistor and said another resistor being configured for adjusting pole-zero compensation.

22. A method for compensation of an output stage, said method comprising the steps of:

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

compensating the output stage through said first compensation capacitor.

23. The method according to claim 22, 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 having a second compensation capacitor, 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 output stage through said first compensation capacitor and said second compensation capacitor.

24. The compensation method according to claim 23, wherein said step of sensing with said first segmented sense device comprises drawing current from a first current source.

25. The compensation method according to claim 24, wherein said step of sensing with said second segmented sense device comprises drawing current from a second current source larger than said first current source.

26. The compensation method according to claim 23, wherein said method further comprises the steps of sensing said output current with a plurality of additional segmented sense devices having a plurality of compensation capacitors, with each of said plurality of additional segmented sense devices being scaled in size, configured to sense multiple levels of output current, and being coupled to a one of a plurality of additional current sources.

27. The compensation method according to claim 26, wherein said plurality of additional current sources is scaled in a manner inversely proportional to said plurality of additional segmented sense devices.

28. The compensation method according to claim 26, wherein said plurality of additional segmented sense devices is configured to multiply compensation effects of said plurality of compensation capacitors.