Intelligent soft start for switching regulators

• US 20070090817A1
• Filed: 10/26/2005
• Published: 04/26/2007
• Est. Priority Date: 10/26/2005
• Status: Active Grant

• Current Assignee: Microchip Technology Incorporated
• Original Assignee: Micrel Incorporated (Microchip Technology Incorporated)
• Inventors: Yee, Philip
• Granted Patent: US 7,408,332 B2
• Time in Patent Office: Days
• US Class Current: 323/282
• CPC Class Codes: G05F 1/468 characterised by reference voltage circuitry, e.g. soft start, remote shutdown
• CPC Class Codes: H02M 1/36 Means for starting or stopping converters
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators

Abstract

A circuit, method, and system for intelligently soft starting switching regulators are provided. The circuit, method, and system provide for a switching circuit operable to couple an input voltage to an output of the switching regulator in response to a control signal, a controller operable to generate the control signal to control the switching of the switching circuit based in part on a reference voltage, and a soft start circuit operable to provide the reference voltage to the controller responsive to the switching of the switching circuit.

Claims

1. A switching regulator comprising:

a switching circuit operable to couple an input voltage to an output of the switching regulator in response to a control signal;

a controller operable to generate the control signal to control the switching of the switching circuit based in part on a reference voltage; and

a soft start circuit operable to provide the reference voltage to the controller responsive to the switching of the switching circuit.

2. The switching regulator of claim 1, wherein the switching circuit comprises:

a first transistor operable to couple the input voltage to the output of the switching regulator in response to the control signal generated by the controller; and

a rectifier operable to direct a current flow in the switching regulator when the input voltage is not coupled to the output of the switching regulator.

3. The switching regulator of claim 2, wherein the rectifier is a diode or a second transistor.

4. The switching regulator of claim 3, wherein the first transistor is a P-channel MOSFET and the second transistor is an N-channel MOSFET.

5. The switching regulator of claim 1, wherein the controller comprises:

an error amplifier operable to generate an output signal based on the reference voltage from the soft start circuit and a feedback from the output of the switching regulator; and

a comparator operable to generate the control signal to control the switching of the switching circuit based on the output signal from the error amplifier and a ramp voltage from an internal circuit.

6. The switching regulator of claim 5, further comprising:

one or more resistors operable to regulate the feedback from the output of the switching regulator to the error amplifier.

7. The switching regulator of claim 1, wherein the soft start circuit comprises:

a filter operable to filter the reference voltage provided to the controller; and

a transistor operable to couple the reference voltage to the filter in response to the control signal generated by the controller.

8. The switching regulator of claim 7, wherein a rate at which the filter in the soft start circuit increases the reference voltage provided to the controller is discontinuous.

9. The switching regulator of claim 7, wherein a rate at which the transistor in the soft start circuit couples the reference voltage to the filter is based on a load coupled to the output of the switching regulator.

10. A method of regulating an input voltage using a switching regulator, the method comprising:

coupling the input voltage to an output of the switching regulator through a switching circuit in the switching regulator in response to a control signal;

generating the control signal at a controller in the switching regulator to control the switching of the switching circuit based in part on a reference voltage; and

providing the reference voltage to the controller through a soft start circuit in the switching regulator responsive to the switching of the switching circuit.

11. The method of claim 10, wherein coupling the input voltage to the output of the switching regulator comprises:

coupling the input voltage to the output of the switching regulator through a transistor in the switching circuit in response to the control signal generated by the controller; and

directing a current flow in the switching regulator through a rectifier in the switching circuit when the input voltage is not coupled to the output of the switching regulator.

12. The method of claim 10, wherein generating the control signal to control the switching of the switching circuit comprises:

generating an output signal at an error amplifier in the controller based on the reference voltage from the soft start circuit and a feedback from the output of the switching regulator; and

generating the control signal to control the switching of the switching circuit at a comparator in the controller based on the output signal from the error amplifier and a ramp voltage from an internal circuit.

13. The method of claim 10, wherein providing the reference voltage to the controller comprises:

filtering the reference voltage provided to the controller through a filter in the soft start circuit; and

coupling the reference voltage to the filter through a transistor in the soft start circuit in response to the control signal generated by the controller.

14. The method of claim 13, wherein a rate at which the filter in the soft start circuit increases the reference voltage provided to the controller is discontinuous.

15. The method of claim 13, wherein a rate at which the transistor in the soft start circuit couples the reference voltage to the filter is based on a load coupled to the output of the switching regulator.

16. A system comprising:

an integrated circuit;

a power source operable to power the integrated circuit; and

a switching regulator operable to regulate a power output from the power source to the integrated circuit, the switching regulator comprising

a switching circuit operable to couple an input voltage to an output of the switching regulator in response to a control signal, wherein the input voltage is provided by the power output from the power source and the output of the switching regulator is connected to the integrated circuit;

a controller operable to generate the control signal to control the switching of the switching circuit based in part on a reference voltage; and

a soft start circuit operable to provide the reference voltage to the controller responsive to the switching of the switching circuit.

17. The system of claim 16, wherein the switching circuit in the switching regulator comprises:

a transistor operable to couple the input voltage to the output of the switching regulator in response to the control signal generated by the controller; and

a rectifier operable to direct a current flow in the switching regulator when the input voltage is not coupled to the output of the switching regulator.

18. The system of claim 16, wherein the controller in the switching regulator comprises:

an error amplifier operable to generate an output signal based on the reference voltage from the soft start circuit and a feedback from the output of the switching regulator; and

a comparator operable to generate the control signal to control the switching of the switching circuit based on the output signal from the error amplifier and a ramp voltage from an internal circuit.

19. The system of claim 16, wherein the soft start circuit in the switching regulator comprises:

a filter operable to filter the reference voltage provided to the controller; and

a transistor operable to couple the reference voltage to the filter in response to the control signal generated by the controller.

20. The system of claim 19, wherein a rate at which the filter in the soft start circuit increases the reference voltage provided to the controller is discontinuous.

21. The system of claim 19, wherein a rate at which the transistor in the soft start circuit couples the reference voltage to the filter in the soft start circuit is based on a load associated with the integrated circuit.