Synchronous buck converter including multi-mode control for light load efficiency and related method

1. A synchronous buck converter comprising:

a multi-mode control circuit for detecting a load condition of a variable load;

an output stage driven by said multi-mode control circuit;

said variable load coupled to said output stage;

said multi-mode control circuit including a first control circuitry for driving said output stage using a first control mode and a second control circuitry different from said first control circuitry for driving said output stage using it second control mode;

a feedback circuit connected between said output stage and said multi-mode control circuit, said feedback circuit configured to provide a first feedback signal to said first control circuitry using a first feedback path, and to provide a second feedback signal to said second control circuitry using a second feedback path;

wherein said multi-mode control circuit adjusts a current provided by said output stage to said variable load based on said load condition.

2. The synchronous buck converter of claim 1 , wherein said multi-mode control circuit is configured to selectably provide a drive signal to said output stage using one of said first control mode and said second control mode according to said load condition.

3. The synchronous buck converter of claim 1 , wherein said multi-mode control circuit is configured to selectably provide a drive signal to said output stage using one of at least said first control mode and said second control mode according to said load condition, and wherein said first control mode is selected for switching efficiency when said load condition is heavy and said second control mode is selected for switching efficiency when said load condition is light.

4. The synchronous buck converter of claim 1 , wherein one control mode selectably used by said multi-mode control circuit to drive said output stage comprises an adaptive ON-time (AOT) mode.

5. The synchronous buck converter of claim 1 , wherein one control mode selectably used by said multi-mode control circuit to drive said output stage comprises an AOT mode; and wherein an ON-time of said AOT mode is determined according to one of said first and second feedback signals received from said feedback circuit.

6. The synchronous buck converter of claim 1 , wherein said multi-mode control circuit is further configured to increase a switching frequency of said output stage if said switching frequency is less than or equal to approximately 25 kHz.

7. The synchronous buck converter of claim 1 , wherein one control mode selectably used by said multi-mode control circuit to drive said output stage comprises a pulse-width modulation (PWM) mode.

8. The synchronous buck converter of claim 1 , wherein said multi-mode control circuit is configured to selectably provide a drive signal to said output stage using one of at least said first control mode and said second control mode according to said load condition, wherein said first control mode is selected for switching efficiency when said load condition is heavy and said second control mode is selected for switching efficiency when said load condition is light, said multi-mode control circuit further configured to delay transition from said first control mode to said second control mode for a delay interval after detecting that said load condition is light.

9. The synchronous buck converter of claim 1 , wherein said multi-mode control circuit comprises a first selective control output coupled to a high-side switch of said output stage and a second selective control output coupled to a low-Side switch of said output stage.

10. The synchronous buck converter of claim 1 , wherein said multi-mode control circuit comprises a first selective control output coupled to a high-side switch of said output stage and a second selective control output coupled to a low-side switch of said output stage, and wherein said first and second selective control outputs comprise respective first and second multiplexers.

11. A method for use in a synchronous buck converter, said method comprising:

driving an output stage of said synchronous buck converter by a multi-mode control circuit including a first control circuitry for driving said output stage using a first control mode and a second control circuitry different from said first control circuitry for driving said output stage using a second control mode;

detecting by said multi-mode control circuit a load condition of a variable load coupled to said output stage;

providing feedback from said output stage to said multi-mode control circuit by a feedback circuit of said synchronous buck converter, said feedback circuit configured to provide a first feedback signal to said first control circuitry using a first feedback path, and to provide a second feedback signal to said second control circuitry using a second feedback path;

adjusting by said multi-mode control circuit a current provided by said output stage to said variable load based on said load condition.

12. The method of claim 11 , wherein driving said output stage of said synchronous buck converter by said multi-mode control circuit comprises selectably providing a drive signal to said output stage using one of said first control mode and said second control mode according to said load condition.

13. The method of claim 11 , wherein driving said output stage of said synchronous buck converter by said multi-mode control circuit comprises selectably providing a drive signal to said output stage using one of at least said first control mode and said second control mode according to said load condition, and wherein said first control mode is selected for switching efficiency when said load condition is heavy and said second control mode is selected for switching efficiency when said load condition is light.

14. The method of claim 11 , wherein one control mode selectably used by said multi-mode control circuit to drive said output stage comprises an adaptive ON-time (AOT) mode.

15. The method of claim 11 , wherein one control mode selectably used by said multi-mode control circuit to drive said output stage comprises an AOT mode, and wherein an ON-time of said AOT mode is determined according to one of said first and second feedback signals received from said feedback circuit.

16. The method of claim 11 , further comprising increasing by said multi-mode control circuit a switching frequency of said output stage if said switching frequency is less than or equal to approximately 25 kHz.

17. The method of claim 11 , wherein one control mode selectably used by said multi-mode control circuit to drive said output stage comprises a pulse-width modulation (PWM) mode.

18. The method of claim 11 , wherein driving said output stage of said synchronous buck converter by said multi-mode control circuit comprises selectably providing a drive signal to said output stage using one of at least said first control mode and said second control mode according to said load condition, wherein said first control mode is selected for switching efficiency when said load condition is heavy and said second control mode is selected for switching efficiency when said load condition is light, said method further comprising delaying a transition from said first control mode to said second control mode for a delay interval after detecting that said load condition is light.

19. The method of claim 11 , wherein said multi-mode control circuit comprises a first selective control output coupled to a high-side switch of said output stage and a second selective control output coupled to a low-side switch of said output stage.

20. The method of claim 11 , wherein said multi-mode control circuit comprises a first selective control output coupled to a high-side switch of said output stage and a second selective control output coupled to a low-side switch of said output stage, and wherein said first and second selective control outputs comprise respective first and second multiplexers.