High slew rate switching regulator circuits and methods

1. An apparatus comprising:

a first switching regulator coupled to an output node;

a second switching regulator coupled to the output node through a capacitor, wherein the capacitor comprises

a first terminal coupled to the output node, and

a second terminal coupled to the second switching regulator; and

a controller configured to regulate a voltage on the output node, wherein the controller comprises

a first feedback input coupled to the first terminal of the capacitor, and

a second feedback input coupled to the second terminal of the capacitor;

wherein the controller is further configured to regulate a voltage on the second terminal of the capacitor,

wherein the first switching regulator is configured to produce a first current slew rate and the second switching regulator is configured to produce a second current slew rate, and wherein the first current slew rate is different than the second current slew rate.

2. The apparatus of claim 1 , wherein the regulated voltage on the second terminal of the capacitor is equal to a difference between an input voltage and the regulated voltage on the output node.

3. The apparatus of claim 1 :

wherein the first switching regulator produces a first current through a first inductor in response to a change in a reference signal; and

the second switching regulator produces the second current through a second inductor in response to the change in the reference signal.

4. The apparatus of claim 1 :

wherein the first switching regulator produces the first current through a first inductor in response to a change in a load current; and

the second switching regulator produces the second current through a second inductor in response to the change in the load current.

5. The apparatus of claim 1 , wherein the first switching regulator generates a first capacitor recharge current and the second switching regulator generates a second capacitor recharge current, wherein a sum of the first capacitor recharge current and the second capacitor recharge current is approximately zero.

6. The apparatus of claim 1 , wherein a first input voltage to the first switching regulator is equal to a second input voltage to the second switching regulator.

7. The apparatus of claim 1 , wherein the first current slew rate corresponds to a rate of change in a first current through a first inductor and the second current slew rate corresponds to a rate of change in a second current through a second inductor.

8. The apparatus of claim 1 , wherein a duty cycle of a first inductor in the first switching regulator is controlled independently of a duty cycle of a second inductor in the second switching regulator.

9. The apparatus of claim 1 , wherein the second switching regulator has a negative current slew rate that is greater than a negative current slew rate of the first switching regulator.

10. The apparatus of claim 1 , wherein the first switching regulator has a positive current slew rate that is greater than a positive current slew rate of the second switching regulator.

11. A method comprising:

receiving a first input voltage in a first switching regulator;

receiving a second input voltage in a second switching regulator; and

controlling the first switching regulator to produce a first current through a first inductor and controlling the second switching regulator to produce a second current through a second inductor and a capacitor to maintain a first regulated voltage on an output node and a second regulated voltage between the second inductor and the capacitor,

wherein the first switching regulator is configured to produce a first current slew rate and the second switching regulator is configured to produce a second current slew rate, and wherein the first current slew rate is different than the second current slew rate.

12. The method of claim 11 , wherein the first input voltage is equal to the second input voltage, and wherein the second regulated voltage is equal to a difference between the first input voltage and the first regulated voltage.

13. The method of claim 11 :

wherein the first switching regulator produces the first current in response to a change in a reference signal; and

the second switching regulator produces the second current in response to the change in the reference signal.

14. The method of claim 11 :

wherein the first switching regulator produces the first current in response to a change in a load current; and

the second switching regulator produces the second current in response to the change in the load current.

15. The method of claim 11 , further comprising:

controlling the first switching regulator to generate a first capacitor recharge current; and

controlling the second switching regulator to generate a second capacitor recharge current;

wherein a sum of the first capacitor recharge current and the second capacitor recharge current is approximately zero.

16. The method of claim 11 , wherein the second switching regulator has a negative current slew rate that is greater than a negative current slew rate of the first switching regulator.

17. The method of claim 11 , wherein the first switching regulator is coupled to a load at the output node, and wherein the second switching regulator is coupled to the load through the capacitor.

18. The method of claim 11 , wherein the first current slew rate corresponds to a rate of change in the first current through the first inductor and the second current slew rate corresponds to a rate of change in the second current through the second inductor.

19. The method of claim 11 , wherein a duty cycle of the first inductor is controlled independently of a duty cycle of the second inductor.

20. The method of claim 11 , wherein the first switching regulator has a positive current slew rate that is greater than a positive current slew rate of the second switching regulator.