Methods and Apparatuses for a Soft-Start Function with Auto-Disable

• US 20130200873A1
• Filed: 02/03/2012
• Published: 08/08/2013
• Est. Priority Date: 02/03/2012
• Status: Active Grant

• Current Assignee: pSemi Corporation (Murata Manufacturing Co Limited)
• Original Assignee: Peregrine Semiconductor Corporation (Murata Manufacturing Co Limited)
• Inventors: Wu, Gary Chunshien
• Granted Patent: US 9,042,135 B2
• Time in Patent Office: Days
• US Class Current: 323/288
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• 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
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence

Abstract

Methods and apparatuses for a soft-start function with auto-disable are described. Such methods and apparatuses can gradually increase a voltage towards a reference voltage using a ramp generator and a control loop and can disable the ramp generator and the control loop once the voltage has reached the reference voltage.

Claims

1. A circuital arrangement, wherein the circuital arrangement is adapted to be coupled to a reference voltage generator, the reference voltage generator being adapted to generate a reference voltage when not coupled to the circuital arrangement, the circuital arrangement comprising:

a ramp generator, wherein, during operation, the ramp generator is configured to generate a ramp voltage that increases in magnitude over time;

a control loop comprising a comparator coupled with a first switching element on one end and the ramp generator on another end, wherein, during operation;

the comparator is adapted to receive the ramp voltage and a soft-start voltage,

the comparator is configured to apply a comparator output voltage to the first switching element, and

the comparator output voltage gradually turns off the first switching element as the ramp voltage increases toward the reference voltage,

wherein the soft-start voltage is a function of the ramp voltage, the comparator output voltage, and the reference voltage.

2. The circuital arrangement according to claim 1, wherein:

the soft-start voltage follows the ramp voltage when the ramp voltage is less than the reference voltage, and

the soft-start voltage follows the reference voltage when the ramp voltage is greater than the reference voltage.

3. The circuital arrangement according to claim 1, wherein:

the first switching element is a field effect transistor, and

the first switching element is outside of subthreshold mode when the ramp voltage is not greater than the reference voltage and is in subthreshold mode when the ramp voltage is greater than the reference voltage.

4. The circuital arrangement according to claim 1, further comprising:

a PMOSFET coupled with the first switching arrangement and the comparator on one end and the ramp generator on another end,

wherein;

the PMOSFET is adapted to receive the ramp voltage and the soft-start voltage, and

during operation, the comparator output voltage gradually turns off the PMOSFET as the ramp voltage increases toward the reference voltage.

5. The circuital arrangement according to claim 1, wherein the ramp generator comprises at least one of:

an RC ramp generator, wherein the RC ramp generator comprises at least one resistor coupled with at least one capacitor, and

a linear ramp generator, wherein the linear ramp comprises a fixed current source and a capacitor, the fixed current source being configured to feed a current to the capacitor.

6. The circuital arrangement according to claim 1, wherein:

the reference voltage generator is a bandgap voltage reference circuit, and

the reference voltage is a function of an output of the bandgap voltage reference circuit.

7. The circuital arrangement according to claim 1, further comprising a second switching element coupled with the ramp generator, wherein:

the second switching element is adapted to receive a control signal,

the second switching element is in a first state when the control signal is at a first voltage and is in a second state when the control signal is at a second voltage, and

the ramp generator and the control loop are in operation when the second switching element is in the second state.

8. The circuital arrangement according to claim 7, wherein the second switching element is turned on in the first state and turned off in the second state.

9. A DC-DC converter, comprising:

the circuital arrangement according to claim 1, wherein the circuital arrangement generates the soft-start voltage; and

a DC-DC conversion unit configured to generate a second voltage waveform based on the soft-start voltage,

wherein a voltage output of the DC-DC converter is a function of the second voltage waveform.

10. The DC-DC converter according to claim 9, wherein the second voltage waveform is a square wave, the DC-DC converter further comprising:

reactive elements coupled with the DC-DC conversion unit and configured to generate the voltage output of the DC-DC converter from the second voltage waveform.

11. The DC-DC converter according to claim 9, further comprising:

a transconductance amplifier coupled with the control loop of the circuital arrangement and adapted to receive the reference voltage and a feedback voltage,

wherein;

the feedback voltage is a function of the voltage output from the DC-DC converter, and

a current output from the DC-DC converter is based on a voltage output from the transconductance amplifier.

18. A method of increasing a soft-start voltage from a first voltage to a second voltage, the second voltage being substantially equal in value to a reference voltage, the method comprising:

providing the circuital arrangement according to claim 7;

applying a control signal to the second switching element of the circuital arrangement such that the ramp generator and the control loop are in operation; and

increasing the soft-start voltage from the first voltage to the second voltage by operating the ramp generator and the control loop.

12. A method of increasing a soft-start voltage from a first voltage to a second voltage, the second voltage being substantially equal in value to a reference voltage, wherein the reference voltage is adapted to be generated via a reference voltage generator, the method comprising:

generating a ramp voltage via a ramp generator, wherein, during operation of the ramp generator, the ramp voltage increases in magnitude over time;

providing a control loop, wherein the control loop comprises a comparator coupled with a first switching element on one end and the ramp generator on another end;

generating a comparator output voltage via the comparator based on the ramp voltage and the soft-start voltage;

providing the first switching element, wherein;

the first switching element is adapted to receive the comparator output voltage, and

the comparator output voltage gradually turns off the first switching element as the ramp voltage increases toward the reference voltage;

providing the first voltage as the soft-start voltage;

increasing the soft-start voltage toward the second voltage when the ramp voltage is less than the reference voltage; and

retaining the soft-start voltage at the second voltage when the ramp voltage is greater than the reference voltage, thus increasing the soft-start voltage from the first voltage to the second voltage.

13. The method according to claim 12, wherein:

the soft-start voltage follows the ramp voltage when the ramp voltage is less than the reference voltage, and

the soft-start voltage follows the second voltage when the ramp voltage is greater than the reference voltage.

14. The method according to claim 12, wherein:

the soft-start voltage is an output of a soft-start circuit,

the reference voltage generator is adapted to generate the reference voltage when not coupled to the soft-start circuit, and

the generating of the ramp voltage, generating of the comparator output voltage, increasing of the soft-start voltage, and retaining of the soft-start voltage is performed during operation of the soft-start circuit.

15. The method according to claim 14, wherein:

the first switching element is a field effect transistor, and

during operation of the soft-start circuit, the first switching element is outside of subthreshold mode when the ramp voltage is not greater than the reference voltage and is in subthreshold mode when the ramp voltage is greater than the reference voltage.

16. The method according to claim 14, further comprising:

providing a PMOSFET coupled with the first switching arrangement and the comparator on one end and the ramp generator on another end,

wherein;

the PMOSFET is adapted to receive the ramp voltage and the soft-start voltage, and

during operation of the soft-start circuit, the comparator output voltage gradually turns off the PMOSFET as the ramp voltage increases toward the reference voltage.

17. The method according to claim 12, wherein:

the ramp generator comprises a resistor and a capacitor;

the resistor and the capacitor are coupled with the comparator; and

the generating of the ramp voltage comprises;

applying a source voltage to the ramp generator, wherein the source voltage is coupled to a first end of the resistor;

generating a current through the resistor based on a voltage difference between the source voltage and voltage at a second end of the resistor; and

generating the ramp voltage based on the current across the resistor, wherein the ramp voltage appears across the capacitor.