Method of forming a semiconductor device
In one embodiment, an LDO circuit is configured to increase a bias current to an error amplifier of the LDO circuit, and to subsequently return the bias current to an earlier value in response to the output current increasing to greater than a threshold current level.
1. A regulator configured as an analog low drop out regulator comprising:
the regulator configured for supplying a load current to a load and forming an output voltage having a desired value;
an error amplifier configured to receive a reference voltage and form the output voltage having the desired value that is substantially representative of the reference voltage;
a differential pair of the error amplifier configured to conduct a first bias current of a first value; and
a bias control circuit configured form an adjust current and use the adjust current to control the error amplifier to increase the first bias current from the first value to a second value in response to the output voltage decreasing to less than the desired value wherein the load current is less than a threshold value prior to the output voltage decreasing, the bias control circuit configured to decrease the adjust current response to the output voltage returning to substantially the desired value.
2. The regulator of claim 1 wherein the bias control circuit decreases the adjust current after the load current increases to greater than the threshold value.
3. The regulator of claim 1 wherein the bias control circuit includes a steering circuit that couples the error amplifier to receive a control current in response to the load current having a value that is less than the threshold value, and to decouple the error amplifier from the control current in response to the load current increasing to greater than the threshold value.
4. The regulator of claim 1 wherein the error amplifier includes a variable current source that conducts the first bias current and wherein the bias control circuit controls the variable current source to change the first value to the second value.
5. The regulator of claim 1 wherein the bias control circuit includes a capacitor configured to form a control current in response to the output voltage decreasing wherein the bias control circuit selectively couples the error amplifier to receive the control current to change the first value to the second value.
6. The regulator of claim 5 further including the bias control circuit configured to decouple the error amplifier from the control current in response to the load current being substantially greater than the threshold value.
7. The regulator of claim 1 wherein the bias control circuit includes a first capacitor coupled to receive the output voltage and configured to form a first control current in response to the output voltage decreasing.
8. The regulator of claim 7 wherein the bias control circuit is configured to couple the first control current to a first variable current source that is coupled commonly to both transistors of the differential pair.
9. The regulator of claim 7 wherein the bias control circuit includes a second capacitor coupled to receive the output voltage and configured to form a second control current in response to the output voltage decreasing.
10. The regulator of claim 9 wherein the bias control circuit is configured to couple a second variable current source of the error amplifier to receive the second control current wherein the second variable current source supplies a second bias current to a first transistor of the differential pair and supplies a third bias current to a second transistor of the differential pair wherein the second bias current is substantially equal to the third bias current.
11. The regulator of claim 1 wherein the bias control circuit includes a steering circuit to selectively couple a control current from the bias control circuit to the error amplifier to increase the first value to the second value.
12. The regulator of claim 1 wherein the bias control circuit includes a first capacitor coupled to receive the output voltage, a first transistor configured to couple a first control current from the first capacitor to a control terminal of a first variable current source, the first variable current source commonly coupled to a second transistor and a third transistor of the differential pair to conduct the first bias current.
13. The regulator of claim 12 further including a second capacitor coupled to receive the output voltage, a fourth transistor configured to couple a second control current from the second capacitor to a control terminal of a second variable current source, the second variable current source having a first output coupled to the second transistor and having a second output coupled to the third transistor.
14. A method of forming a low dropout regulator comprising:
configuring an output for forming an output voltage and an output current for supplying to a load;
configuring an error amplifier to receive a reference voltage and form the output voltage having a desired value;
configuring the low dropout regulator to selectively couple the error amplifier to a bias adjust circuit responsively to the output current having a value that is less than a threshold value wherein the bias adjust circuit subsequently forms an adjust signal to have a value that increases a bias current of the error amplifier from a first value to a second value in response to the output voltage decreasing to less than the desired value; and
configuring the bias adjust circuit to subsequently decouple the error amplifier from receiving the adjust signal in response to the output current increasing to no less than the threshold value.
15. The method of claim 14 including configuring a differential pair of the error amplifier to conduct the bias current of the first value.
16. The method of claim 15 including configuring a variable current source of the error amplifier to form the bias current.
17. The method of claim 14 including configuring the bias adjust circuit to not change the first value in response to output voltage changes subsequently to the output current being greater than the threshold value.
18. The method of claim 14 including configuring the bias adjust circuit to form the control current as a current through a capacitor in response to the output voltage decreasing and to couple the control current to a current source of the error amplifier to change the first value to the second value.
19. A method of forming a low drop out regulator comprising:
configuring an error amplifier of the low drop out regulator to receive a reference voltage and form an output voltage having a desired value and form an output current;
configuring a bias control circuit to selectively increase a bias current of the error amplifier from a first value to a second value in response to the output voltage decreasing to less than the desired value; and
configuring the bias control circuit to subsequently decouple the error amplifier from receiving the control current in response to the output current increasing to no less than a threshold value.
20. The method of claim 19 including configuring the bias control circuit to selectively couple the error amplifier for receiving the control current in response to the output current decreasing to less than the threshold value.