Over-voltage protection circuit and method therefor

1. An over-voltage protection circuit of a power supply controller comprising:

a control circuit coupled to receive a first PWM control signal and responsively form a first control signal operable to control a first transistor to control a output voltage and coupled to receive a second PWM control signal and responsively form a second control signal operable to control a second transistor to control the output voltage;

the control circuit configured to block the first PWM control signal and the second PWM control signal responsively to an over-voltage value of the output voltage;

the control circuit configured to assert the second control signal and negate the first control signal responsively to a first voltage value of the output voltage that is less than the over-voltage value; and

the control circuit configured to negate the second control signal and negate the first control signal responsively to a second voltage value of the output voltage that is greater than the first voltage value and less than the over-voltage value.

2. The over-voltage protection circuit of the power supply controller of claim 1 wherein the control circuit configured to assert the second control signal and negate the first control signal includes the control circuit configured to assert the second control signal subsequently to being negated responsively to the over-voltage value.

3. The over-voltage protection circuit of the power supply controller of claim 1 wherein the control circuit configured to assert the second control signal and negate the first control signal includes the control circuit configured to negate the second control signal subsequently to being asserted responsively to the first voltage value.

4. The over-voltage protection circuit of the power supply controller of claim 1 further including a PWM controller configured to generate the first PWM control signal and the second PWM control signal responsively to the output voltage.

5. The over-voltage protection circuit of the power supply controller of claim 4 further including an error amplifier coupled to receive a feedback signal representative of the output voltage and responsively form an error signal wherein the error signal is coupled to the PWM controller.

6. The over-voltage protection circuit of the power supply controller of claim 1 wherein the control circuit configured to block the first PWM control signal and the second PWM control signal responsively to the over-voltage value of the output voltage includes a detector coupled to detect the over-voltage value and responsively block the first PWM control signal from the first control signal and to block the second PWM control signal from the second control signal.

7. The over-voltage protection circuit of the power supply controller of claim 1 wherein the control circuit includes a comparator configured to detect the first voltage value and the second voltage value and to responsively control the first control signal and the second control signal.

8. A method of forming an over-voltage protection circuit of a power supply controller comprising:

configuring the power supply controller to control an output voltage;

configuring the over-voltage protection circuit to assert a first control signal to enable a first power transistor of the power supply controller responsively to an over-voltage value of the output voltage;

configuring the over-voltage protection circuit to subsequently negate the first control signal to disable the first power transistor responsively to a first voltage value of the output voltage; and

configuring the over-voltage protection circuit to subsequently assert the first control signal to enable the first power transistor responsively to a second voltage value of the output voltage wherein the second voltage value is greater than the first voltage value and less than the over-voltage value.

9. The method of claim 8 further including configuring the over-voltage protection circuit to negate the first control signal to disable the first power transistor responsively to the first voltage value of the output voltage subsequently to enabling the first power transistor responsively to the second voltage value.

10. The method of claim 8 wherein configuring the over-voltage protection circuit to control the output voltage and assert the first control signal to enable the first power transistor responsively to the over-voltage value of the output voltage includes configuring the over-voltage protection circuit to disable a second power transistor responsively to the over-voltage value and to continue disabling the second power transistor while the first control signal is subsequently negated and asserted.

11. The method of claim 8 wherein the over-voltage protection circuit and the power supply controller are formed on a semiconductor die.

12. The method of claim 8 wherein configuring the power supply controller to control the output voltage includes configuring a PWM controller of the power supply controller to generate a first PWM control signal and a second PWM control signal responsively to the output voltage and coupling the first control signal to block the second PWM control signal responsively to the over-voltage value.

13. The method of claim 12 wherein coupling the first control signal to override the second PWM control signal responsively to the over-voltage value includes coupling the first control signal to block the second PWM control signal responsively to the over-voltage value, the first voltage value and the second voltage value.

14. The method of claim 13 wherein configuring the over-voltage protection circuit to subsequently assert the first control signal to enable the first power transistor includes configuring over-voltage protection circuit to disable a second power transistor while enabling the first power transistor.

15. A method of operating an over-voltage protection circuit of a power supply controller comprising:

detecting an over-voltage value of an output voltage of a power supply system;

disabling an upper power transistor of an output stage of the power supply system responsively to the over-voltage value; and

alternately enabling and disabling a lower power transistor of the output stage responsively to respective first and second values of the output voltage.

16. The method of claim 15 wherein disabling the upper power transistor of the output stage of the power supply system responsively to the over-voltage value includes blocking a first PWM control signal from the upper power transistor responsively to the over-voltage value.

17. The method of claim 16 wherein alternately enabling and disabling the lower power transistor of the output stage includes blocking a second PWM control signal from the lower power transistor responsively to the over-voltage value and asserting a control signal to enable the lower power transistor responsively to the first value, and negating the control signal to disable the lower power transistor responsively to the second value.

18. The method of claim 17 including asserting the control signal to enable the lower power transistor subsequently to blocking the first PWM control signal and the second PWM control signal.

19. The method of claim 17 including negating the second control signal to disable the lower power transistor subsequently to asserting the control signal to enable the lower power transistor.

20. The method of claim 15 wherein alternately enabling and disabling the lower power transistor of the output stage responsively to respective first and second values of the output voltage includes alternately enabling and disabling the lower power transistor for multiple cycles and disabling the upper power transistor while alternately enabling and disabling the lower power transistor.