Method and circuitry for compensating low dropout regulators

Patent metadata

Field	Value
Publication number	US-11009900-B2
Application number	US-201715400976-A
Country	US
Kind code	B2
Filing date	Jan 7, 2017
Priority date	Jan 7, 2017
Publication date	May 18, 2021
Grant date	May 18, 2021

Abstract

Low dropout regulators (LDOs) are disclosed herein. An example of an LDO includes an error amplifier having a first input and a second input, wherein the first input is for coupling to an output of the LDO and the second input for coupling to a reference voltage. The error amplifier has an output with a voltage that is proportional to the difference between the output voltage and the reference voltage. A second amplifier is coupled between the error amplifier and the output of the LDO. A gain boost amplifier is coupled between the error amplifier and the second amplifier. The gain boost amplifier increases DC gain of the LDO in response to a load step on the output.

First claim

What is claimed:

1. A low dropout regulator (LDO) comprising:
an error amplifier having a first input and a second input, the first input for coupling to an output of the LDO and the second input for coupling to a reference voltage, the error amplifier operable to output a voltage proportional to the difference between the output voltage of the LDO and the reference voltage;
a second amplifier having an input coupled to the error amplifier and an output coupled to the output of the LDO;
a gain boost amplifier coupled between the output of the error amplifier and the input of the second amplifier, the gain boost amplifier operable to change the DC gain of the LDO in response to a load step on the output; and
wherein the error amplifier comprises a differential amplifier having a tail current and wherein the tail current is set in response to the output of the error amplifier.

2. The LDO of claim 1 , wherein the gain boost amplifier is further operable to reduce the DC gain of the error amplifier in response to the load step on the output of the LDO.

3. The LDO of claim 1 , wherein the tail current is increased in response to the error amplifier indicating a difference between a voltage at the output of the LDO and the reference voltage, and wherein the tail current is decreased in response to the error amplifier indicating the voltage at the output of the LDO and the reference voltage being substantially the same.

4. The LDO of claim 1 , wherein the error amplifier has a differential output coupled to the input of a differential amplifier, wherein the tail current is set in response to the output of the differential amplifier.

5. The LDO of claim 1 , wherein the gain boost amplifier is operable to regulate current flow through the second amplifier.

6. The LDO of claim 1 , wherein the gain boost amplifier is a differential amplifier, and further comprising a filter coupled between inputs of the differential amplifier.

7. The LDO of claim 1 , further comprising a common gate amplifier coupled to the output of the error amplifier, the output of the common gate amplifier coupled to a transistor and is operable to control the tail current of the error amplifier.

8. A low dropout regulator (LDO) comprising:
an error amplifier having a first input and a second input, the first input for coupling to an output of the LDO and the second input for coupling to a reference voltage, the error amplifier operable to output a voltage proportional to the difference between the output voltage of the LDO and the reference voltage;
a second amplifier having an input coupled to the error amplifier and an output coupled to the output of the LDO;
a gain boost amplifier coupled between the output of the error amplifier and the input of the second amplifier, the gain boost amplifier operable to change the DC gain of the LDO in response to a load step on the output; and
a pass transistor having a drain and source coupled between a voltage input to the LDO and the output of the LDO, the gate of the pass transistor being coupled to an input of the gain boost amplifier and an output of the second amplifier.

9. The LDO of claim 8 , wherein the second amplifier is a differential amplifier, the gain boost amplifier is a differential amplifier, and wherein the gate of the pass transistor is coupled to a first output of the second amplifier and a first input of the gain boost amplifier.

10. The LDO of claim 9 , wherein a second output of the second amplifier is coupled to a second input of the gain boost amplifier.

11. A method for compensating a low dropout regulator (LDO), the LDO having an error amplifier coupled to a second amplifier, the method comprising:
receiving a first voltage that is proportional to an output voltage of the LDO;
comparing the first voltage to a reference voltage using the error amplifier;
changing the gain of the error amplifier in response to comparing the first voltage to the reference voltage, wherein the change of gain provides gain boost to the output of the LDO; and
changing the DC gain of the LDO in response to the comparing, wherein the changing the gain of the LDO reduces the difference between the first voltage and the reference voltage; and
wherein the LDO comprises a differential amplifier having inputs coupled to the reference voltage and the first voltage, the differential amplifier operable to compare the first voltage to the reference voltage; wherein the differential amplifier has a tail current and wherein changing the gain of the error amplifier comprises changing the tail current.

12. The method of claim 11 , wherein changing the tail current comprises:
increasing the tail current in response to the output voltage being different than the reference voltage; and
decreasing the tail current in response to the output voltage being substantially the same as the reference voltage.

13. The method of claim 11 , wherein the second amplifier has a current flow that is proportional to the gain of the second amplifier, and wherein changing the DC gain of the LDO in response to the comparing includes changing the current flow through the second amplifier.

14. A low dropout regulator (LDO) comprising:
an input for coupling to an input voltage;
an output for providing an output voltage;
a pass transistor coupled between the input and the output;
an error amplifier operable to compare the output voltage to a reference voltage and generate an error signal proportional to the difference between the output voltage and the reference voltage;
circuitry for controlling the gain of the error amplifier in response to the error signal;
a second amplifier having an output to the gate of the pass transistor;
a current regulator for controlling the gain of the second amplifier;
a gain boost amplifier coupled between the error amplifier and the second amplifier, the output of the gain boost amplifier for controlling the current regulator; and
a filter coupled between differential inputs of the gain boost amplifier.

15. The LDO of claim 14 , wherein the current regulator is a transistor having a gate coupled to the output of the gain boost amplifier.

16. A low dropout regulator (LDO) having an error amplifier and a gain boosting amplifier nested within the LDO, the LDO comprising:
an LDO input;
an LDO output,
the error amplifier (EA) having a first EA input, a second EA input, a first EA output and a second EA output, the error amplifier including:
a first transistor having a first current terminal, a second current terminal connected to the first EA output, and a first control terminal connected to the first EA input; and
a second transistor having a third current terminal connected to the first current terminal, a fourth current terminal connected to the second EA output, and a second control terminal connected to the LDO output;

a third transistor having a fifth current terminal, a sixth current terminal and a third control terminal connected to the fifth current terminal;
a pass transistor having a seventh current terminal connected to a first supply rail having a first supply potential, an eighth current terminal coupled to a second supply rail having a second supply potential different than the first supply potential, and a pass control terminal;
the gain boosting amplifier (GBA) having a first GBA input coupled to the third current terminal, a second GBA input coupled to the third current terminal and a GBA output, the gain boosting amplifier operable to cause a potential at the third control terminal to track a potential at the pass control terminal.

Assignees

• Texas Instruments Inc

Inventors

• Ivanov Vadim Valerievich
• Sriraj Sahana

Classifications

• G05F1/40 Primary

  using discharge tubes or semiconductor devices as final control devices · CPC title

• G05F1/563

  including two stages of regulation at least one of which is output level responsive, e.g. coarse and fine regulation · CPC title

• G05F1/575 Primary

  characterised by the feedback circuit · CPC title