System and method for pre-charging a bootstrap capacitor in a switching regulator with high pre-bias voltage

• US 8,154,334 B2
• Filed: 11/03/2009
• Issued: 04/10/2012
• Est. Priority Date: 07/21/2009
• Status: Active Grant

• Current Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Original Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Inventors: Wang, Jue
• Primary Examiner(s): Donovan, Lincoln
• Assistant Examiner(s): Cole, Brandon S
• Application Number:
  US12/611,701
• Publication Number:
  US 20110018613A1
• Time in Patent Office: 889 Days
• Field of Search: 327/148, 327/157, 327534-537, 363/59, 363/60
• US Class Current: 327/537
• CPC Class Codes: H02M 3/1588 comprising at least one synchronous rectifier element H02M3/1582, H02M3/1584 take precedence
• CPC Class Codes: H03K 2217/0081 Power supply means, e.g. to the switch driver
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

An apparatus comprises a voltage regulator including an high side switching transistor and a low side switching transistor. An high side drive controls operation of the high side switching transistor. A low side driver controls operation of the low side switching transistor. A bootstrap capacitor provides an operating voltage to the high side switching driver. The bootstrap capacitor is charged to a predetermined level responsive to a supply voltage. A low side driver drives the low side switching transistor according to a process that charges the bootstrap capacitor to the predetermined level. The process turns on the low side switching transistor for a first predetermined number of cycles and turns off the low side switching transistor for a second predetermined number of cycles. The process is repeated for a predetermined number of times during startup of the voltage regulator when a prebias load is applied to the voltage regulator.

Claims

1. An apparatus, comprising:

a voltage regulator including an high side switching transistor and a low side switching transistor;

a high side driver for controlling operation of the high side switching transistor;

a low side driver for controlling operation of the low side switching transistor;

a bootstrap capacitor for providing an operating voltage to the high side driver, the bootstrap capacitor charged to a predetermined level responsive to a supply voltage prior to application of a PWM control signal to the high side driver and the low side driver; and

wherein the low side driver drives the low side switching transistor according to a process that charges the bootstrap capacitor to the predetermined level prior to application of the PWM control signal to the high side driver and the low side driver, the process maintaining the high side switching transistor in an off state and turning on the low side switching transistor for a first predetermined number of cycles and turning off the low side switching transistor for a second predetermined number of cycles and repeating the process for predetermined number of times during startup of the voltage regulator when a prebias load is applied to the voltage regulator until the bootstrap capacitor is charged to the predetermined level.

2. The apparatus of claim 1, wherein a voltage on the bootstrap capacitor increases and a magnitude of a negative inductor current of the voltage regulator increases when the low side switching transistor is turned on and the magnitude of the negative inductor current of the voltage regulator decreases when the low side switching transistor is turned off.

3. The apparatus of claim 1, further including a switching circuit for connecting the supply voltage to the bootstrap capacitor when the low side switching transistor is turned on.

4. The apparatus of claim 3, wherein the switching circuit further comprises:

at least one switching circuit responsive to at least one switching control signal; and

a bootstrap capacitor switching control block for generating the at least one switching control signal.

5. The apparatus of claim 1, wherein the voltage regulator does not generate a PWM signal until the bootstrap capacitor has been charged to the predetermined level.

6. The apparatus of claim 1, wherein the voltage regulator further comprises:

an inductor connected at a phase node between the high side switching transistor and the low side switching transistor and an output voltage node; and

a capacitor connected between the output voltage node and ground.

7. An apparatus, comprising:

a voltage regulator including high side switching circuitry, low side switching circuitry and a bootstrap capacitor for providing an operating voltage to the high side switching circuitry; and

wherein the voltage regular includes a startup mode of operation to charge the bootstrap capacitor to a predetermined level by maintaining the high side switching transistor in an off state and turning on the low side switching circuitry for a first predetermined number of cycles and turning off the low side switching circuitry for a second predetermined number of cycles and repeating the process of turning on and off the low side switching circuitry for a predetermined number of times during startup of the voltage regulator when a prebias load is applied to the voltage regulator prior to application of a PWM control signal within the voltage regulator.

8. The apparatus of claim 7, wherein a voltage on the bootstrap capacitor increases and a magnitude of a negative inductor current of the voltage regulator increases when the low side switching circuitry is turned on and the magnitude of the negative inductor current of the voltage regulator decreases when the low side switching circuitry is turned off

9. The apparatus of claim 7, further including a switching circuit for connecting a supply voltage to the bootstrap capacitor when the low side switching circuitry is turned on.

10. The apparatus of claim 7, wherein the voltage regulator generates a PWM signal in a post startup mode of operation after the bootstrap capacitor has been charged to the predetermined level.

11. A method for charging a bootstrap capacitor in a voltage regulator, comprising the steps of:

a) initiating a startup process for the voltage regulator when a prebias load is applied to the voltage regulator prior to application of a PWM control signal;

b) maintaining a high side switching transistor in an off state during the start up process;

c) turning on a low side switching transistor for a first predetermined number of clock cycles during the start up process;

d) turning off the low side switching transistor for a second predetermined number of clock cycles during the start up process;

e) repeating steps c)-d) for a predetermined number of times to charge the bootstrap capacitor to a predetermined voltage level while maintaining a negative inductor current in a predetermined range;

f) applying the PWM control signal to drive the high side transistor and low side transistor after the bootstrap capacitor reaches the predetermined voltage level.

12. The method of claim 11, wherein the step of turning on the low side switching transistor further comprises the steps of:

increasing a voltage on the bootstrap capacitor responsive to the low side switching transistor being turned on; and

increasing a magnitude of the negative inductor current of the voltage regulator when the low side switching transistor is turned on.

13. The method of claim 11, wherein the step of turning off the low side switching transistor further comprises the steps of decreasing the magnitude of the negative inductor current of the voltage regulator when the low side switching transistor is turned off.

14. The method of claim 11, further including the step of connecting a supply voltage to the bootstrap capacitor when the low side switching transistor is turned on.

15. The method of claim 11, further including the step of generating a PWM signal after the bootstrap capacitor has been charged to the predetermined level.