Dual input self-referenced voltage regulator
An apparatus for voltage regulation is disclosed. In some implementations, the apparatus includes: a first voltage regulator configured to generate a regulated voltage at an output based on a first supply voltage on a first voltage rail; a second voltage regulator configured to generate the regulated voltage at the output based on a second supply voltage on a second voltage rail; and a control circuit configured to: maintain the first and second voltage regulators generating the regulated voltage at the same time in response to a first condition; and prevent cross-coupling of the second supply voltage to the first voltage rail in response to a second condition.
1 . An apparatus, comprising:
a first voltage regulator configured to generate a regulated voltage at an output based on a first supply voltage on a first voltage rail, wherein the first voltage regulator comprises
a first field effect transistor (FET), a second FET, a first resistive device, and a second resistive device coupled in series between the first voltage rail and a third voltage rail, wherein a first node between the second FET and the first resistive device is coupled to the output, and
a first Brokaw cell including an input coupled to a second node between the first and second resistive devices and an output coupled to gates of the first and second FETs, respectively;
a second voltage regulator configured to generate the regulated voltage at the output based on a second supply voltage on a second voltage rail; and
a control circuit configured to:
maintain the first and second voltage regulators generating the regulated voltage at the same time in response to a first condition; and
prevent a cross-coupling of the second supply voltage to the first voltage rail in response to a second condition.
2 . The apparatus of claim 1 , wherein the first condition comprises the first supply voltage being greater than the second supply voltage.
3 . The apparatus of claim 1 , wherein the second condition comprises the first supply voltage being less than the second supply voltage.
4 . The apparatus of claim 1 , wherein the control circuit comprises a first comparator configured to generate a first control signal based on the first and second supply voltages, wherein the first voltage regulator comprises a field effect transistor (FET) coupled between the first voltage rail and the output, wherein the FET is configured to turn off based on the first control signal.
5 . The apparatus of claim 4 , wherein the FET is configured to generate the regulated voltage in response to the first control signal indicating that the first supply voltage is greater than the second supply voltage.
6 . The apparatus of claim 4 , wherein the FET is configured to turn off in response to the first control signal indicating that the first supply voltage is less than the second supply voltage.
7 . The apparatus of claim 1 , wherein the control circuit is further configured to prevent a cross-coupling of the first supply voltage to the second voltage rail in response to a third condition.
8 . The apparatus of claim 7 , wherein the third condition comprises the second supply voltage being less than the regulated voltage.
9 . The apparatus of claim 8 , wherein the third condition comprises the second supply voltage being greater than the first supply voltage.
10 . The apparatus of claim 9 , wherein the control circuit comprises:
a first comparator configured to generate a first control signal based on the first and second supply voltages; and
a second comparator configured to generate a second control signal based on the second supply voltage and the regulated voltage, wherein the second comparator is configured to be enabled based on the first control signal.
11 . The apparatus of claim 10 , wherein the second comparator is configured to be enabled in response to the first control signal indicating that the first supply voltage is greater than the second supply voltage.
12 . The apparatus of claim 11 , wherein the second voltage regulator comprises a field effect transistor (FET) coupled between the second voltage rail and the output, wherein the FET is configured to turn off based on the second control signal.
13 . The apparatus of claim 12 , wherein the FET is configured to turn off in response to the second control signal indicating that the second supply voltage is less than the regulated voltage.
14 . The apparatus of claim 1 , wherein the second voltage regulator comprises:
a third FET, a fourth FET, a third resistive device, and a fourth resistive device coupled in series between the second voltage rail and the third voltage rail, wherein a third node between the fourth FET and the third resistive device is coupled to the output; and
a second Brokaw cell including an input coupled to a fourth node between the third and fourth resistive devices and an output coupled to gates of the third and fourth FETs, respectively.
15 . The apparatus of claim 14 , wherein the first, second, third, and fourth resistive devices are configured to provide a first feedback voltage to the input of the first Brokaw cell greater than a second feedback voltage provided to the input of the second Brokaw cell.
16 . The apparatus of claim 1 , wherein at least one of the first or second voltage regulator comprises a Brokaw cell.
17 . The apparatus of claim 16 , wherein the Brokaw cell comprises:
a first field effect transistor (FET), a second FET, a third FET, and a first bipolar junction transistor (BJT) coupled between a first node and a second node;
a fourth FET, a fifth FET, a sixth FET, and a second BJT, and a first resistive device coupled between the first node and the second node;
a second resistive device coupled between the second node and a third voltage rail;
a third resistive device coupled between gates of the third and sixth FETs, respectively; and
a fourth resistive device coupled between bases of the first and second BJTs, respectively;
wherein gates of the first and third FETs are coupled together, and gates of the second and fourth FETs are coupled together.
18 . The apparatus of claim 17 , wherein the first, second, fourth, and fifth FETs are p-channel FETs, and wherein the third and sixth FETs are n-channel FETs.
19 . The apparatus of claim 17 , wherein a size of the second BJT is greater than a size of the first BJT.
20 . A method, comprising:
generating a regulated voltage at an output based on a first supply voltage on a first voltage rail based on a first condition;
generating the regulated voltage based on a second supply voltage on a second voltage rail on a second condition, wherein the second condition comprises the first supply voltage being greater than the second supply voltage and the second supply voltage being greater than the regulated voltage; and
decoupling the first voltage rail from the output in response to a third condition.
21 . The method of claim 20 , wherein the first condition comprises the first supply voltage being greater than the second supply voltage.
22 . The method of claim 20 , wherein the third condition comprises the first supply voltage being less than the second supply voltage.
23 . The method of claim 20 , further comprising decoupling the second voltage rail from the output in response to a fourth condition.
24 . The method of claim 23 , wherein the fourth condition comprises the second supply voltage being greater than the first supply voltage.
25 . An apparatus, comprising:
a first voltage regulator configured to generate a regulated voltage at an output based on a first supply voltage on a first voltage rail;
a second voltage regulator configured to generate the regulated voltage at the output based on a second supply voltage on a second voltage rail; and
a control circuit configured to:
couple the first and second voltage rails to the output at the same time in response to a first condition; and
decouple the first voltage rail from the output in response to a second condition, wherein the second condition comprises the first supply voltage being greater than the second supply voltage and the second supply voltage being greater than the regulated voltage.
26 . The apparatus of claim 25 , wherein the first condition comprises the first supply voltage being greater than the second supply voltage.
27 . The apparatus of claim 25 , wherein the second condition comprises the first supply voltage being less than the second supply voltage.
28 . An apparatus, comprising:
means for generating a regulated voltage at an output based on a first supply voltage on a first voltage rail based on a first condition;
means for generating the regulated voltage based on a second supply voltage on a second voltage rail on a second condition, wherein the second condition comprises the first supply voltage being greater than the second supply voltage and the second supply voltage being greater than the regulated voltage; and
means for decoupling the first voltage rail from the output in response to a third condition.