Soft-start circuit for switching regulator

• US 9,484,800 B2
• Filed: 03/05/2014
• Issued: 11/01/2016
• Est. Priority Date: 03/05/2014
• Status: Active Grant

• Current Assignee: Tower Semiconductor Limited
• Original Assignee: Tower Semiconductor Limited
• Inventors: Faingersh, Alexander, Sarig, Erez
• Primary Examiner(s): Berhane, Adolf
• Assistant Examiner(s): DEMISSE, AFEWORK S
• Application Number:
  US14/198,477
• Publication Number:
  US 20150256060A1
• Time in Patent Office: 972 Days
• Field of Search: 323/234, 323/237, 323/265, 323/266, 323273-275, 323282-285
• US Class Current: 1/1
• 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 soft-start circuit for a switching regulator (e.g., a buck converter) in which the soft-start circuit supplies a DC ramp voltage to the switch regulator'"'"'s pre-driver such that the pulsed gate voltage supplied to power switch during the initial soft-start operating phase includes a series of pulses having amplitudes that respectively gradually change (e.g., sequentially increase from 0V to the system operating voltage), whereby the regulated output voltage passed from the power switch to the load is gradually increased at a rate that prevents voltage overshoot and inrush current. The DC ramp voltage is generated, for example, by a current source that begins charging a capacitor at the beginning of the initial soft-start operating phase. This arrangement allows a constant-frequency ramp signal generated by a single oscillator to be shared by multiple switch regulators that are fabricated on an IC chip.

Claims

1. An integrated circuit comprising:

a load circuit;

a switching regulator for supplying a regulated output voltage to the load circuit, the switching regulator comprising;

a switch control circuit including means for generating a pulsed gate voltage signal;

a power switch coupled to a system operating voltage source and the load and having a gate terminal connected to receive the pulsed gate voltage signal; and

a soft-start circuit including means for generating a direct current (DC) ramp voltage that gradually changes between a first voltage and a second voltage during an initial soft-start operating phase,

wherein soft-start circuit is coupled to supply the the DC ramp voltage to the switch control circuit such that an amplitude of the pulsed gate voltage gradually changes between the first and second voltages during the initial soft-start phase, and

wherein the soft-start circuit comprises a ramp generator circuit coupled to the gate terminal of one of a PMOS source-follower transistor transistor and an NMOS source-follower transistor, and means for activating the ramp generator at the beginning of the initial soft-start operating phase.

2. The integrated circuit of claim 1,

wherein the switch control circuit comprises:

a comparator configured to generate an amplifier control signal in response to a portion of the regulated output voltage and a predetermined reference voltage;

a pulse width modulator (PWM) circuit configured to generate a pulse signal in response to an oscillating ramp signal and the amplifier control signal; and

an amplifier configured to generate said pulsed gate voltage signal in response to the pulse signal, and

wherein the soft-start circuit is coupled to the amplifier such that the DC ramp voltage is supplied to a power terminal of the amplifier.

3. The integrated circuit of claim 1,

wherein the integrated circuit comprises two or more said switching regulators, two or more load circuits respectively coupled to receive regulated voltages from said two or more said switching regulators, said soft-start circuit, and an oscillator that are fabricated on a semiconductor substrate, and

wherein a constant-frequency ramp signal generated by said oscillator is transmitted to each of said two or more switching regulators.

4. The integrated circuit of claim 3, wherein both of the two or more said switching regulators are coupled to receive said DC ramp voltage generated by said soft-start circuit.

5. The integrated circuit of claim 1, wherein the ramp generator circuit comprises means for generating one of a linear ramp voltage and a non-linear ramp voltage.

6. The integrated circuit of claim 1, wherein the ramp generator circuit comprises a current source coupled to a capacitor.

7. The integrated circuit of claim 1,

wherein the switching regulator comprises a buck converter;

wherein the power switch comprises an n-channel transistor; and

wherein the soft-start circuit comprises means for generating said DC ramp voltage such that said DC ramp voltage gradually increases from said first voltage to said second voltage during said initial soft-start operating phase, whereby the amplitude of the pulsed gate voltage incrementally increases between the first voltage and the second voltages during the initial soft-start phase.

8. The integrated circuit of claim 1,

wherein the switching regulator comprises a boost converter;

wherein the power switch comprises a p-channel transistor; and

wherein the soft-start circuit comprises means for generating said DC ramp voltage such that said DC ramp voltage gradually decreases from said second voltage to said first voltage during said initial soft-start operating phase, whereby the amplitude of the pulsed gate voltage gradually decreases from the second voltage to the first voltage during the initial soft-start phase.

9. The integrated circuit of claim 1, wherein the soft-start circuit further comprises means for coupling a constant system voltage to the switch control circuit after completion of the initial soft-start phase.

10. The soft-start circuit of claim 1,

wherein the switching regulator comprises a boost converter;

wherein the power switch comprises a p-channel transistor; and

wherein said means for generating said DC ramp voltage comprises means for causing said DC ramp voltage to gradually decrease from said second voltage to said first voltage during said initial soft-start operating phase, whereby the amplitude of the pulsed gate voltage gradually decreases from the second voltage to the first voltage during the initial soft-start phase.

11. A soft-start circuit for a switching regulator utilized to supply a regulated output voltage to a load circuit, the switching regulator including:

a switch control circuit including;

a comparator configured to generate an amplifier control signal in response to a portion of the regulated output voltage and a predetermined reference voltage,

a pulse width modulator (PWM) configured to generate a pulse signal in response to an oscillating ramp signal and the amplifier control signal, and

an amplifier configured to generate a pulsed gate voltage signal in response to the pulse signal; and

a power switch coupled to a system operating voltage source and the load circuit and having a gate terminal connected to receive the pulsed gate voltage signal,

wherein the soft-start circuit comprises means for generating a direct current (DC) ramp voltage that gradually changes between a first voltage and a second voltage during an initial soft-start operating phase,

wherein the soft-start circuit is coupled to supply the DC ramp voltage to a power terminal of the amplifier such that an amplitude of each sequentially occurring voltage pulse of a series of voltage pulses making up the pulsed gate voltage gradually changes between the first and second voltages during the initial soft-start phase in accordance with the DC ramp voltage, and

wherein the associated amplitudes of at least some of the sequentially occurring said voltage pulses causes the switch control circuit to partially turn on such that a voltage generated on an output terminal of the power switch gradually changes during the initial soft-start phase at a rate that prevents voltage overshoot in the load circuit.

12. The soft-start circuit of claim 11,

wherein the switching regulator comprises a buck converter;

wherein the power switch comprises an n-channel transistor; and

wherein said means for generating said DC ramp voltage comprises means for causing said DC ramp voltage to gradually increase from said first voltage to said second voltage during said initial soft-start operating phase, whereby the amplitude of the pulsed gate voltage gradually increases from the first voltage to the second voltage during the initial soft-start phase.

13. A method for generating a soft-start in a switching regulator, the switching regulator including a switch control circuit for generating a pulsed gate voltage signal, and a power switch coupled between a system operating voltage source and a load circuit and having a gate terminal connected to receive the pulsed gate voltage signal, the method comprising:

generating a direct current (DC) ramp voltage that gradually changes between a first voltage and a second voltage during an initial soft-start phase; and

generating the pulsed gate voltage signal including a series of sequential voltage pulses such that an associated amplitude of each sequentially occurring said voltage pulse of the series of voltage pulses incrementally changes between the first and second voltages during the initial soft-start phase in accordance with the DC ramp voltage, wherein the associated amplitudes of at least some of the sequentially occurring said voltage pulses causes the switch control circuit to partially turn on such that an output voltage supplied to the load circuit gradually increases to a system voltage level during the initial soft-start phase.

14. The method of claim 13,

wherein the switch control circuit further comprises:

a comparator for generating an amplifier control signal in response to a portion of the regulated output voltage and a predetermined reference voltage;

a pulse width modulator (PWM) for generating a pulse signal in response to an oscillating ramp signal and the amplifier control signal; and

an amplifier for generating said pulsed gate voltage signal in response to the pulse signal, and

wherein using the DC ramp voltage to control the switch control circuit comprises supplying the DC ramp voltage a power terminal of the amplifier.

15. The method of claim 13, wherein generating the DC ramp voltage comprises coupling a ramp generator circuit to one or said first or second voltages at the beginning of the initial soft-start operating phase.

16. The method of claim 13, wherein generating said DC ramp voltage comprises generating one of a linear ramp voltage and a non-linear ramp voltage.

17. The method of claim 13, further comprising coupling a constant system voltage to the switch control circuit after completion of the initial soft-start phase.

18. The method of Claim 13,

wherein the switching regulator comprises a buck converter;

wherein the power switch comprises an n-channel transistor; and

wherein generating said DC ramp voltage comprises causing said DC ramp voltage to gradually increase from said first voltage to said second voltage during said initial soft-start operating phase, whereby the amplitude of the pulsed gate voltage gradually increases from the first voltage to the second voltage during the initial soft-start phase.

19. The method of claim 13,

wherein the switching regulator comprises a boost converter;

wherein the power switch comprises a p-channel transistor; and

wherein generating said DC ramp voltage comprises causing said DC ramp voltage to gradually decrease from said second voltage to said first voltage during said initial soft-start operating phase, whereby the amplitude of the pulsed gate voltage gradually decreases from the second voltage to the first voltage during the initial soft-start phase.