Voltage regulator with optimal efficiency selection and a master-slave zero cross detection configuration

1. A voltage regulator comprising:

a first phase power stage including:

a first high side transistor configured to activate and deactivate to regulate an input voltage;

a first low side transistor coupled to the first high side transistor, the first low side transistor configured to deactivate when a current level in the first phase power stage is substantially equal to zero; and

a zero cross detection circuit in communication with the first low side transistor, the zero cross detection circuit configured to measure the current level for the first phase power stage, and to deactivate the first low side transistor when the current level is substantially equal to zero;

a second phase power stage connected in parallel with the first phase power stage, the second phase power stage including:

a second high side transistor configured to activate and deactivate to regulate the input voltage; and

a second low side transistor coupled to the second high side transistor, the second low side transistor configured to deactivate in response to a signal from the zero cross detection circuit, the signal indicating when the current level in the first phase power stage is substantially equal to zero; and

a controller coupled to the first phase power stage and to the second phase power stage, the controller configured to measure an output current of the voltage regulator and to activate the second phase power stage when the output current is above a first threshold current level.

2. The voltage regulator of claim 1 further comprising:

a third phase power stage including:

a third high side transistor configured to activate and deactivate to regulate the input voltage; and

a third low side transistor coupled to the third high side transistor, the third low side transistor configured to deactivate in response to the signal from the zero cross detection circuit, the signal indicates when the current level in the first phase power stage is substantially equal to zero.

3. The voltage regulator of claim 2 wherein the controller is further configured to enable the third phase power stage when the output current is above a second threshold current level.

4. The voltage regulator of claim 1 wherein the first phase power stage further includes:

a drive circuit coupled to the first high side transistor and to the first low high side transistor, the drive circuit configured to control the first high side transistor and the first low side transistor.

5. The voltage regulator of claim 1 wherein the current level is measured in the low side transistor.

6. The voltage regulator of claim 1 wherein the current level is measure based on a current through an inductor.

7. The voltage regulator of claim 1 wherein the first high side transistor, the first low side transistor, the second high side transistor, and the second low side transistor are metal-oxide-semiconductor-field-effect-transistors (MOSFETs).

8. A voltage regulator comprising:

a first phase power stage including a zero cross detection circuit configured to measure a current level for the first phase power stage, to set a first flag in a first driver of the first phase power stage when the current level is substantially equal to zero, and to cause a diode emulation state in the first phase power stage in response to the first flag being set in the first driver;

a second phase power stage in communication with the zero cross detection circuit, the second phase power stage configured to set a second flag in a second driver of the second phase power stage in response to a signal from the zero cross detection circuit, and to enter the diode emulation state in response to the second flag being set in the second driver; and

a controller coupled to the first phase power stage and to the second phase power stage, the controller configured to measure an output current of the voltage regulator and to activate the second phase power stage when the output current is above a first threshold current level.

9. The voltage regulator of claim 8 further comprising:

a third phase power stage in communication with the zero cross detection circuit, the third phase power stage configured to enter the diode emulation state in response to receiving a signal from the zero cross detection circuit.

10. The voltage regulator of claim 9 wherein the controller is further configured to enable the third phase power stage when the output current is above a second threshold current level.

11. The voltage regulator of claim 8 wherein the diode emulation state of the first phase power stage and the second phase power stage prevents an opposite current flow in the first phase power stage and the second phase power stage.

12. The voltage regulator of claim 8 wherein the current level is measured in a low side transistor of the first phase power stage.

13. The voltage regulator of claim 8 wherein the current level is measure based on a current through an inductor.

14. A method comprising:

enabling a first phase power stage and a second phase power stage in a voltage regulator;

detecting that an output current of the voltage regulator is below a first threshold current;

disabling a third phase power stage when the output current of the voltage regulator is below the first threshold current;

measuring a current in a first low side transistor in the first phase power stage;

detecting that the current in the first low side transistor is below a zero detect threshold;

setting a flag in the voltage regulator when the current in the first low side transistor is below a zero detect threshold;

detecting, in the first phase power stage and the second phase power stage, that the flag is set; and

disabling the first low side transistor in the first phase power stage and a second low side transistor in the second phase power stage when the flag is set.

15. The method of claim 14 further comprising:

detecting that the current in the first low side transistor is above the zero detect threshold;

unsetting the flag in the voltage regulator when the current in the first low side transistor is above the zero detect threshold;

detecting, in the first phase power stage and the second phase power stage, that the flag is unset;

enabling the first low side transistor and the second low transistor when the flag is unset;

detecting that the output current of the voltage regulator is above the first threshold current;

enabling the third phase power stage when the output current of the voltage regulator is above the first threshold current; and

enabling a third low side transistor in the third phase power stage when the flag is unset.

16. The method of claim 15 further comprising:

detecting that the current in the first low-side transistor is below a second threshold current; and

disabling the second phase power stage and the third phase power stage in response to the current in the first low-side transistor is below the second threshold current.

17. The method of claim 16 wherein the second threshold current is less than the first threshold current.

18. The method of claim 14 wherein the current level is measured in the low side transistor.

19. The method of claim 14 wherein the current level is measure based on a current through an inductor.

20. The method of claim 14 wherein the first low side transistor and the second low side transistor are metal-oxide-semiconductor-field-effect-transistors (MOSFETs).