Stable low dropout voltage regulator controller

• US 5,686,821 A
• Filed: 05/09/1996
• Issued: 11/11/1997
• Est. Priority Date: 05/09/1996
• Status: Expired due to Term

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Brokaw, Adrian P.
• Primary Examiner(s): BERHANE, ADOLF D
• Application Number:
  US08/647,241
• Time in Patent Office: 551 Days
• Field of Search: 323/273, 323/280, 323/277, 323/281, 323/313, 323/314, 323/315, 323/316
• US Class Current: 323/273
• CPC Class Codes: G05F 1/575 characterised by the feedback circuit

Abstract

A single-loop voltage regulator controller includes a high-gain transconductance amplifier that accommodates common mode inputs as low as its negative supply rail. The input stage of the amplifier produces a proportional to absoulte temperature (PTAT) input offset voltage. The transconductance amplifier'"'"'s inverting input is connected to the circuit common, or negative supply rail, and a tap from a feedback network is connected to the amplifier'"'"'s noninverting input. The feedback network provides, at this tap, a PTAT measure of the regulator'"'"'s regulated output. The amplifier'"'"'s output is connected to drive a noninverting driver which, in turn, is connected to drive the control terminal of the regulator'"'"'s pass transistor. A compensation capacitor connected between the amplifier'"'"'s output and the regulated output terminal ensures the regulator'"'"'s stability even for relatively low level load impedances.

Claims

1. A low dropout voltage regulator controller for connection with a pass transistor to produce a low dropout voltage regulator, comprising:

a common supply terminal,

a control terminal connectable to the control terminal of a pass transistor,

an unregulated voltage input terminal connectable to a current conducting terminal of a pass transistor,

a regulated voltage output terminal connectable to another current conducting terminal of a pass transistor,

a single-loop feedback controller connected between said regulated voltage output terminal and said pass transistor control terminal, said feedback controller including a transconductance amplifier having an output, said feedback controller connected to provide a control signal which, when connected to said pass transistor control terminal produces a regulated output voltage at said regulated voltage output terminal which is substantially independent of the regulator'"'"'s load and operating temperature, and

a pole-splitting compensation capacitor connected between the output of said transconductance amplifier and said regulated voltage output terminal which splits the regulator'"'"'s poles to improve the stablilty of the regulator.

2. The controller of claim 1, wherein said single-loop feedback controller comprises:

a feedback circuit having a tap connected between said regulated output and common terminals, said circuit producing a proportional to absolute temperature (PTAT) signal, available at said tap, that is representative of the voltage at the regulated output terminal.

3. The controller of claim 2, wherein said single-loop feedback controller further comprises a differential input transconductance amplifier with a common mode input range that includes the common supply voltage, said amplifier further including a PTAT offset voltage at one of said inputs, said input being connected to the tap of the feedback circuit.

4. The controller of claim 3, wherein said single-loop feedback controller further comprises a non-inverting driver connected between the output of said amplifier and said pass transistor control terminal.

5. The controller of claim 4, wherein said single-loop feedback controller further comprises a compensation capacitor connected between said amplifier output and said regulated output terminal.

6. The controller of claim 5, wherein said amplifier comprises:

a differential input stage having inverting and noninverting inputs that accommodate common mode signals as low as its common supply voltage, said input stage connected to produce a PTAT input offset voltage, said inverting input connected to said common supply terminal and said output coupled to said pass transistor control terminal through said noninverting driver.

7. The controller of claim 6, wherein said differential input stage comprises:

a differential pair of PNP transistors having ratioed emitters, with their bases connected to provide said inverting and noninverting inputs, their collectors connected to said common supply terminal and their emitters connected to receive biasing currents.

8. The controller of claim 7, wherein said amplifier further comprises:

a ratioed current mirror connected to provide current to said differential pair and to amplify the PTAT offset voltage across said inverting and noninverting inputs.

9. The controller of claim 8, wherein said amplifier further comprises:

a bias circuit connected to provide bias current to said current mirror, and

a differential to single-ended converter connected to convert an amplified differential signal from said differential pair into a single-ended signal and to modulate the current mirror bias current in response to variations in said amplified differential signal.

10. A low dropout voltage regulator having an unregulated voltage input terminal, a regulated voltage output terminal, and a common terminal, comprising:

a pass transistor having two current conducting terminals connected to said voltage input terminal, the other current conducting terminal connected to said regulated voltage output terminal,

a single-loop feedback controller connected between said regulated voltage output terminal and said pass transistor control terminal, said controller including a transconductance amplifier having an output, said controller connected to provide a control signal which, when connected to said pass transistor control terminal produces a regulated output voltage which is substantially independent of the regulator'"'"'s load and operating temperature, and

a pole-splitting compensation capacitor connected between the output of said transconductance amplifier and said regulated voltage output terminal which splits the regulator'"'"'s poles to improve the stability of the regulator.

11. The voltage regulator of claim 10, wherein said single-loop feedback controller comprises:

a feedback circuit having a tap connected between said regulated output and common terminals, said circuit producing a 5 PTAT signal, available at said tap, that is representative of the voltage at the regulated output terminal.

12. The regulator of claim 11, wherein said single-loop feedback controller further comprises a differential input transconductance amplifier with a common mode input range that includes the common supply voltage, said amplifier further including a proportional to absolute temperature offset voltage at one of said inputs, said input being connected to the tap of the feedback circuit.

13. The regulator of claim 12, wherein said single-loop feedback controller further comprises a non-inverting driver connected between the output of said amplifier and said pass transistor control terminal.

14. The regulator of claim 13, wherein said single-loop feedback controller further comprises a compensation capacitor connected between said amplifier output and said regulated output terminal.

15. The regulator of claim 14, wherein said amplifier comprises:

a differential input stage having inverting and noninverting inputs that accommodate common mode signals as low as its common supply voltage, said input stage connected to produce a PTAT input offset voltage, said inverting input connected to said common supply terminal and said output coupled to said pass transistor control terminal through said noninverting driver.

16. The regulator of claim 15, wherein said differential input stage comprises:

a differential pair of PNP transistors having ratioed emitters, with their bases connected to provide said inverting and noninverting inputs, their collectors connected to said common supply terminal and their emitters connected to receive biasing currents.

17. The regulator of claim 16, wherein said amplifier further comprises:

a ratioed current mirror connected to provide current to said differential pair and to amplify the PTAT offset voltage across said inverting and noninverting inputs.

18. The regulator of claim 17, wherein said amplifier further comprises:

a bias circuit connected to provide bias current to said current mirror, and

a differential to single-ended converter connected to convert an amplified differential signal from said differential pair into a single-ended signal and to modulate the current mirror bias current in response to variations in said amplified differential signal.

19. A low dropout voltage regulator having an unregulated voltage input terminal, a regulated voltage output terminal, and a common terminal, comprising:

a pass transistor having two current conducting terminals and one control terminal, one of said current conducting terminals connected to accept an unregulated input voltage, the other current conducting terminal connected to provide said regulated voltage output,

a noninverting driver connected to drive said control terminal of said pass transistor,

a differential amplifier having inverting and non-inverting inputs and an output, said amplifier being connected at its inverting input to a negative voltage supply and at its output to said control terminal of the pass transistor through said noninverting driver, and an input stage that accommodates common mode signals as low as the amplifier'"'"'s negative supply rail, said input stage also connected to produce a PTAT input offset voltage,

a feedback circuit connected to sense the voltage across said regulated voltage output terminal and said common terminal and to provide at a tap terminal a PTAT signal that is representative of said voltage across said regulated voltage output and common terminals, said tap terminal connected to the noninverting input of said amplifier, and

a compensation capacitor connected from the output of said amplifier to said regulated voltage output terminal.

20. The voltage regulator of claim 19, wherein said amplifier comprises:

a differential pair of bipolar transistors having ratioed emitters, said transistors connected to produce a PTAT offset voltage across said inverting and noninverting inputs.

21. The voltage regulator of claim 20, wherein said amplifier further comprises:

a ratioed current mirror connected to provide current to said differential pair and to amplify the PTAT offset voltage across said inverting and noninverting inputs.

22. The voltage regulator of claim 21, wherein said amplifier further comprises:

a bias circuit connected to provide bias current to said current mirror, and

a differential to single-ended converter connected to convert an amplified differential signal from said differential pair into a single-ended signal and to modulate the bias current in response to variations in said amplified differential signal.

23. The voltage regulator of claim 22, wherein said noninverting driver comprises:

a low-gain, wide-band amplifier.

24. The voltage regulator of claim 23, wherein said noninverting driver comprises:

a unity gain inverting amplifier connected to be driven by said differential amplifier, and

a drive transistor having two current conducting terminals and a control terminal, one of said drive transistor current conducting terminals coupled to the negative voltage terminal, the other current conducting terminal coupled to the control terminal of said pass transistor, and the control terminal of said drive transistor connected to be driven by the unity gain inverting amplifier.

25. The voltage regulator of claim 23, wherein said noninverting driver comprises:

a drive transistor having two current conducting terminals and a control terminal, the control terminal coupled to be driven by said differential to single ended converter, one of said drive transistor current conducting terminals coupled to the negative supply terminal, and the other current conducting terminal coupled to the control terminal of said pass transistor, said drive transistor connected to produce a voltage swing at the control terminal of said pass transistor which is in phase with the voltage swing of the differential to single-ended converter.

26. The voltage regulator of claim 25, wherein said driver further comprises:

a resistor network connected to provide starter current for said pass transistor and a current steering circuit connected to modulate the control terminal of said drive transistor in phase with the signal from the differential to single-ended converter.

27. The voltage regulator of claim 25, wherein said drive transistor is a PNP transistor with its emitter coupled to the control terminal of said pass transistor.

28. The voltage regulator of claim 25, wherein said drive transistor is a p-channel FET.

29. The voltage regulator of claim 25, wherein said feedback circuit comprises:

a first voltage divider having a tap connected connected across said regulated output and negative supply terminals,

a diode connected at its anode to the tap of said first voltage divider, and

a second voltage divider connected between the cathode of said diode and said negative supply terminal, and at its tap to said noninverting input of said amplifier.

30. The voltage regulator of claim 29, wherein said first voltage divider is ratioed to produce an open circuit voltage equal to the bandgap voltage at its tap whenever the voltage at the regulated output terminal equals a prescribed value.