Method of forming a power supply controller and device therefor

1. A semiconductor device having a power supply controller comprising:

a power switch;

a ramp generator configured to form a ramp signal having a periodically occurring period;

a first control circuit configured to form a switching drive signal having the period to operate the power switch and control an output voltage within a desired range around a target value;

a feedback circuit configured to form a feedback signal that is representative of the output voltage;

a current sense circuit configured to from a sense signal that is representative of a current through the power switch;

a second control circuit operably coupled to modulate one of the feedback signal or the sense signal and form a modulated control signal wherein the second control circuit is configured to use only one terminal of the semiconductor device to set a level of the modulation; and

the first control circuit operably coupled to use the modulated control signal to control a duty cycle of the switching drive signal.

2. The semiconductor device having the power supply controller of claim 1 wherein the second control circuit receives the ramp signal and forms a control current that modulates a value of the sense signal.

3. The semiconductor device having the power supply controller of claim 2 wherein the second control circuit is configured to use a resistor external to the semiconductor device to establish a value of the control current and wherein the second control circuit is configured to steer the control current through the only one terminal.

4. The semiconductor device having the power supply controller of claim 2 wherein the control current has a ramp shape that is summed with the sense signal.

5. The semiconductor device having the power supply controller of claim 1 wherein the second control circuit receives the ramp signal and forms a control current that modulates a value of the feedback signal.

6. The semiconductor device having the power supply controller of claim 5 wherein the second circuit is configured to form the control current with a negative going ramp shape that is subtracted from the feedback signal.

7. The semiconductor device having the power supply controller of claim 1 wherein the second control circuit includes a first transistor having a control electrode coupled to receive the ramp signal and a first current carrying electrode coupled to the only one terminal of the semiconductor device.

8. The semiconductor device having the power supply controller of claim 7 wherein the feedback signal is modulated to form the modulated control signal and the modulated control signal is compared to the sense signal to control the duty cycle of the power switch.

9. The semiconductor device having the power supply controller of claim 7 wherein the sense signal is modulated to form the modulated control signal and the modulated control signal is compared to the feedback signal to control the duty cycle of the power switch.

10. A method of forming a power supply controller comprising:

configuring the power supply controller to generate a ramp signal having a period;

configuring the power supply controller to generate a switching drive signal having the period to control an output voltage to a desired range around a target value

configuring the power supply controller to receive a feedback signal that is representative of the output voltage and responsively form a feedback control signal that is representative of the feedback signal; and

configuring the power supply controller to modulate the feedback control signal with the ramp signal to form a modulated control signal.

11. The method of claim 10 further including configuring the power supply controller to form a sense signal that is representative of a current used to form the output voltage during an active portion of the switching drive signal, and configuring the power supply controller to compare the modulated control signal to the sense signal and responsively control a duty cycle of the switching drive signal.

12. The method of claim 10 wherein configuring the power supply controller to generate the switching drive signal includes configuring the power supply controller to generate the ramp signal having the period.

13. The method of claim 10 wherein configuring the power supply controller to modulate the feedback control signal with the ramp signal to form the modulated control signal includes configuring a control circuit of the power supply controller to receive the ramp signal and use a resistor external to the power supply controller to control a level of the modulation of the modulated control signal.

14. The method of claim 10 wherein configuring the power supply controller to modulate the feedback control signal with the ramp signal to form the modulated control signal includes configuring the power supply controller to use the ramp signal to form a first current that is representative of the ramp signal and to use the first current to modulate the feedback signal.

15. The method of claim 14 wherein configuring the power supply controller to use the ramp signal to form the first current that is representative of the ramp signal includes coupling a first control electrode of a first transistor to receive the ramp signal and coupling a first current carrying electrode of the first transistor to an input terminal of a semiconductor device wherein a resistor external to the semiconductor device controls a value of the first current.

16. The method of claim 15 wherein further including forming the semiconductor device to include the first transistor and at least a portion of the power supply controller.

17. A method of forming a semiconductor device having a power supply controller comprising:

configuring the power supply controller to generate a first ramp signal that repeats with a first period;

configuring the power supply controller to generate a switching drive signal having the first period to control an output voltage to a desired range around a target value;

configuring a first control circuit of the power supply controller to receive a feedback signal that is representative of the output voltage;

configuring the first control circuit to receive a sense signal that is representative of a current used to form the output voltage;

configuring the power supply controller to modulate a signal selected from the group consisting of the feedback signal or the sense signal with the first ramp signal to form a modulated control signal; and

configuring the first control circuit to use the modulated control signal to control a duty cycle of the switching drive signal.

18. The method of claim 17 wherein configuring the power supply controller to modulate the signal selected from the group consisting of the feedback signal or the sense signal with the first ramp signal to form the modulated control signal includes configuring the power supply controller to modulate the sense signal and to compare the modulated sense signal to the feedback signal.

19. The method of claim 17 wherein configuring the power supply controller to modulate the signal selected from the group consisting of the feedback signal or the sense signal with the first ramp signal to form the modulated control signal includes coupling a second control circuit to form a modulation signal that is representative of the first ramp signal and to use the modulation signal to modulate the sense signal.

20. The method of claim 19 wherein coupling the second control circuit to form the modulation signal that is representative of the first ramp signal and to use the modulation signal to modulate the sense signal includes forming on a semiconductor die the first control circuit, the second control circuit, and a power switch that is coupled to receive the switching drive signal and further including coupling one terminal of the semiconductor die to use an element external to the semiconductor die to adjust a value of the modulation signal.