SWITCH MODE CONVERTER THAT ALLOWS 100% DUTY CYCLE ON GATE DRIVER

• US 20040080963A1
• Filed: 10/25/2002
• Published: 04/29/2004
• Est. Priority Date: 10/25/2002
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Grant, David A.
• Granted Patent: US 6,812,782 B2
• Time in Patent Office: Days
• US Class Current: 363/59
• CPC Class Codes: H02M 1/08 Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
• CPC Class Codes: H02M 3/1588 comprising at least one synchronous rectifier element H02M3/1582, H02M3/1584 take precedence
• 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

A switch mode converter uses the bootstrap capacitor 30 to operate all the way to 100% duty cycle by adding only a very small amount of low-area extra circuitry. The additional circuitry includes a charge pump 40 and a duty cycle detect device 42. When the duty cycle detect device 42 detects that the converter is attempting to operate in 100% duty cycle, the charge pump 40 provides additional charge to the bootstrap capacitor 30 to ensure that the 100% duty cycle is maintained. Performance into dropout (when the input supply is actually lower than the desired output) is improved. A significant advantage in some applications (notably battery operation) is provided.

Claims

1. A switch mode converter circuit comprising:

a high side transistor;

a low side transistor coupled to the high side transistor;

an inductor having a first end coupled to a node between the high side transistor and the low side transistor and a second end coupled to an output node;

a boot capacitor having a first end coupled to the first end of the inductor;

a high side driver coupled to a control node of the high side transistor;

a first diode coupled between a second end of the boot capacitor and an input voltage node; and

a charge pump for providing additional charge to the boot capacitor when a duty cycle of the switch mode converter circuit is one hundred percent.

2. The circuit of claim 1 further comprising a duty cycle detect device for determining when the duty cycle is one hundred percent.

3. The circuit of claim 1 wherein the charge pump is coupled to the second end of the boot capacitor.

4. The circuit of claim 3 further comprising a second diode coupled between the charge pump and the second end of the boot capacitor.

5. The circuit of claim 1 wherein the second end of the boot capacitor is coupled to a first supply voltage node of the high side driver.

6. The circuit of claim 5 wherein a second supply voltage node of the high side driver is coupled to the node between the high side transistor and the low side transistor.

7. The circuit of claim 5 wherein the charge pump is coupled to the second end of the boot capacitor.

8. The circuit of claim 7 further comprising a second diode coupled between the charge pump and the second end of the boot capacitor.

9. The circuit of claim 1 wherein the charge pump is coupled to the control node of the high side transistor.

10. The circuit of claim 9 wherein a first switch is coupled between the charge pump and the control node of the high side transistor.

11. The circuit of claim 10 wherein a second switch is coupled between the high side driver and the control node of the high side transistor.

12. The circuit of claim 11 further comprising a duty cycle detect device for controlling the first switch and the second switch.

13. A method for controlling a switch mode converter circuit comprising:

providing an inductor;

providing a high side switch coupled to the inductor;

providing a low side switch coupled to the inductor;

providing a boot capacitor coupled between the inductor and an input node;

providing additional charge to the boot capacitor from charge pump when the high side switch reaches a one hundred percent duty cycle.

14. A method for controlling a switch mode converter circuit comprising:

providing an inductor;

providing a high side transistor coupled to the inductor;

providing a low side transistor coupled to the inductor;

providing a boot capacitor coupled between the inductor and an input node;

providing additional charge to a control node of the high side transistor from a charge pump when the high side transistor reaches a one hundred percent duty cycle.