Method and apparatus for synchronous rectifier

1. A method for controlling a drive signal in a synchronous rectifier controller (SRC), the method comprising:

detecting a beginning of a conduction phase using a current sense signal;

in response to detecting the beginning of the conduction phase, commencing an exception timer, commencing a first blanking interval, and asserting the drive signal; and

in response to an OFF condition being detected, the first blanking interval being elapsed, and the exception timer being running, de-asserting the drive signal and commencing a second blanking interval; and

in response to an ON condition being detected, the second blanking interval being elapsed, and the exception timer being running, commencing a third blanking interval and asserting the drive signal.

2. The method of claim 1 , further comprising:

de-asserting the drive signal in response to the OFF condition being detected and the exception timer being lapsed.

3. The method of claim 2 , further comprising:

de-asserting the drive signal in response to the OFF condition being detected, the second blanking interval being lapsed, and the exception timer being lapsed.

4. The method of claim 2 , wherein detecting the beginning of the conduction phase comprises:

detecting the ON condition and that the exception timer is not running.

5. The method of claim 2 , further comprising:

detecting the ON condition in response to the current sense signal falling below an ON threshold.

6. The method of claim 2 , further comprising:

detecting the OFF condition in response to the current sense signal rising above an OFF threshold.

7. The method of claim 1 , wherein a duration of the third blanking interval is the same as a duration of the first blanking interval, and

wherein a duration of the second blanking interval is a predetermined fraction of the duration of the first blanking interval.

8. A Synchronous Rectifier Controller (SRC), comprising:

an exception timer; and

control logic that:

detects a beginning of a conduction phase;

in response to the beginning of the conduction phase being detected, commences the exception timer and performs a first assertion of a drive signal;

in response to detecting an OFF condition, de-asserts the drive signal; and

in response to detecting an ON condition and that the exception timer is running, performs a second assertion of the drive signal.

9. The SRC of claim 8 , further comprising:

one or more blanking timers;

wherein the control logic:

in response to detecting the OFF condition and that the exception timer is running, directs the one or more blanking timers to generate a first blanking interval; and

in response to determining that the first blanking interval has not lapsed, prevents the detection of the ON condition.

10. The SRC of claim 9 , wherein the control logic:

directs the one or more blanking timers to generate a second blanking interval in response to the control logic asserting the drive signal; and

in response to determining that the second blanking interval has not lapsed, prevents the detection of the OFF condition.

11. The SRC of claim 10 , wherein a duration of the first blanking interval is a predetermined fraction of a duration of the second blanking interval.

12. The SRC of claim 8 , further comprising:

an ON comparator that detects the ON condition by comparing a current sense signal to an ON threshold.

13. The SRC of claim 12 , further comprising:

an OFF comparator that detects the OFF condition by comparing the current sense signal to an OFF threshold.

14. The SRC of claim 8 , wherein a duration of the exception timer is externally configurable.

15. A semiconductor device including a synchronous rectifier controller, comprising:

an exception timer;

one or more blanking timers; and

control logic that:

detects a beginning of a conduction phase;

in response to detecting the beginning of the conduction phase, commences the exception timer and performs a first assertion of a drive signal;

in response to detecting an OFF condition, de-asserts the drive signal;

in response to detecting the OFF condition and that the exception timer is running, directs the one or more blanking timers to generate a first blanking interval;

in response to determining that the first blanking interval has not lapsed, prevents the detection of an ON condition; and

in response to detecting the ON condition is detected and that the exception timer is running, performs a second assertion of the drive signal.

16. The semiconductor device of claim 15 , wherein the control logic:

directs the one or more blanking timers to generate a second blanking interval in response to the control logic asserting the drive signal; and

in response to determining that the second blanking interval has not lapsed, prevents the detection of the OFF condition.

17. The semiconductor device of claim 16 , wherein a duration of the first blanking interval is a predetermined fraction of a duration of the second blanking interval.

18. The semiconductor device of claim 15 , further comprising:

an ON comparator that detects the ON condition by comparing a current sense signal to an ON threshold.

19. The semiconductor device of claim 15 , further comprising:

an OFF comparator that detects the OFF condition by comparing the current sense signal to an OFF threshold.

20. The semiconductor device of claim 15 , wherein a duration of the exception timer is externally configurable.