Circuits and methods for controlling a charge pump system

1. A circuit comprising:

a first charge pump coupled to a first switch and operable for providing a first control voltage to said first switch; and

a feedback circuit coupled to said first charge pump and operable for receiving said first control voltage and for adjusting an operating frequency of said first charge pump based upon said first control voltage, wherein said first control voltage is adjusted to a predetermined target voltage by adjusting said operating frequency through said feedback circuit, wherein said feedback circuit comprises:

a sensor coupled to said first switch and operable for generating a sense voltage indicative of said first control voltage;

a first converter coupled to said sensor and operable for generating a first sense current based upon said sense voltage, wherein said first sense current is proportional to a differential voltage between said sense voltage and a reference voltage; and

an oscillator coupled to said first converter and operable for adjusting said operating frequency based upon said first sense current.

2. The circuit of claim 1 , further comprising:

a second switch coupled to said first switch;

a second charge pump coupled to said second switch and operable for providing a second control voltage to said second switch; and

a second converter coupled to said second switch and operable for generating a second sense current based upon said second control voltage, wherein said oscillator adjusts said operating frequency based upon said first sense current and said second sense current, and wherein said first charge pump and said second charge pump share said operating frequency.

3. The circuit of claim 2 , wherein said oscillator adjusts said operating frequency based upon a sum of said first sense current and said second sense current.

4. The circuit of claim 1 , wherein said first converter includes a P channel metal oxide semiconductor field effect transistor (PMOSFET), and wherein said reference voltage is a threshold voltage of said PMOSFET.

5. The circuit of claim 1 , wherein said first sense current is cut off when said first control voltage is less than a predetermined clamp voltage.

6. The circuit of claim 1 , wherein said first charge pump operates at a predetermined maximum frequency when said first control voltage is less than a predetermined clamp voltage.

7. The circuit of claim 1 , wherein said first switch comprises an NMOSFET, and wherein said first control voltage is a gate-to-source voltage of said NMOSFET.

8. A method comprising:

providing a control voltage by a charge pump;

controlling a status of a switch based upon said control voltage;

generating a sense voltage indicative of said control voltage, wherein said sense voltage is proportional to said control voltage;

generating a sense current based upon said sense voltage;

adjusting an operating frequency of said charge pump based upon said sense current; and

adjusting said control voltage to a predetermined target voltage by adjusting said operating frequency.

9. The method of claim 8 , wherein said sense current is proportional to a differential voltage between said sense voltage and a reference voltage.

10. The method of claim 8 , further comprising:

cutting off said sense current when said control voltage is less than a predetermined clamp voltage.

11. The method of claim 8 , further comprising:

controlling said charge pump to operate at a predetermined maximum frequency when said control voltage is less than a predetermined clamp voltage.

12. The method of claim 8 , wherein said switch comprises an NMOSFET, and wherein said control voltage is a gate-to-source voltage of said NMOSFET.

13. A system comprising:

a power source;

a switch coupled to said power source and operable for controlling a connection of said power source to an electronic device based upon a control voltage;

a charge pump coupled to said switch and operable for providing said control voltage; and

a feedback circuit coupled between said switch and said charge pump and operable for adjusting an operating frequency of said charge pump based upon said control voltage to a balance frequency, wherein said feedback circuit comprises:

a sensor coupled to said switch and operable for generating a sense voltage indicative of said control voltage;

a converter coupled to said sensor and operable for generating a sense current based upon said sense voltage; and

an oscillator coupled to said converter and operable for adjusting said operating frequency based upon said sense current.

14. The system of claim 13 , wherein said converter includes a PMOSFET, and wherein said sense current is proportional to a differential voltage between said sense voltage and a threshold voltage of said PMOSFET.

15. The system of claim 13 , wherein said sense current is cut off when said control voltage is less than a predetermined clamp voltage.

16. The system of claim 13 , wherein said charge pump operates at a predetermined maximum frequency when said control voltage is less than a predetermined clamp voltage.

17. The system of claim 13 , wherein said switch comprises an NMOSFET, and wherein said control voltage is a gate-to-source voltage of said NMOSFET.

18. The system of claim 13 , wherein said sense voltage is proportional to said control voltage.