Circuit for charging a bootstrap capacitor in a voltage converter

• US 7,741,901 B2
• Filed: 02/05/2008
• Issued: 06/22/2010
• Est. Priority Date: 02/08/2007
• Status: Active Grant

• Current Assignee: Richtek Technology Corporation (MediaTek, Inc.)
• Original Assignee: Richtek Technology Corporation (MediaTek, Inc.)
• Inventors: Chen, Isaac Y., Lu, Sao-Hung
• Primary Examiner(s): Riley; Shawn
• Application Number:
  US12/068,253
• Publication Number:
  US 20080218141A1
• Time in Patent Office: 868 Days
• Field of Search: 327/589, 323/283, 323/284, 323/224, 323/266
• US Class Current: 327/589
• CPC Class Codes: H03K 17/162 without feedback from the output circuit to the control circuit
• CPC Class Codes: H03K 17/6871 the output circuit comprising more than one controlled field-effect transistor

Abstract

For charging a bootstrap capacitor in a voltage converter, a circuit is provided for wider bandwidth to eliminate the feedback stability issue and pin out for compensation circuit. A pair of transistors are connected in series between a power input and the bootstrap capacitor, the first transistor is switched synchronously with a low-side transistor of the voltage converter, and a comparator compares a feedback voltage drawn from a feedback node between the pair of transistors with a reference voltage, to control the second transistor to determine to charge the bootstrap capacitor.

Claims

1. A circuit for charging a bootstrap capacitor in a voltage converter having a high-side transistor and a low-side transistor connected in series and switched by a high-side driver and a low-side driver respectively, the bootstrap capacitor being connected between a source of the high-side transistor and a high-side power input of the high-side driver, the circuit comprising:

a first transistor connected between the bootstrap capacitor and a feedback node, for being switched synchronously with the low-side transistor;

a dedicated comparator for comparing a feedback voltage drawn from the feedback node with a reference voltage, to produce a control signal, the dedicated comparator being operable without a compensation circuit; and

a second transistor controlled by the control signal, for determining to connect a supply voltage to the feedback node to charge the bootstrap capacitor.

3. The circuit of claim 1, further comprising a voltage divider for dividing a voltage on the feedback node to produce the feedback voltage.

4. The circuit of claim 1, wherein the first transistor is a MOSFET or WET.

5. The circuit of claim 1, wherein the second transistor is a MOSFET or JFET.

2. A circuit for charging bootstrap capacitor in a voltage converter having a high-side transistor and a low-side transistor connected in series and switched by a high-side driver and a low-side driver respectively, the bootstrap capacitor being connected between a source of the high-side transistor and a high-side power input of the high-side driver, the circuit comprising:

a first transistor connected between the bootstrap capacitor and a feedback node, for being switched synchronously with the low-side transistor;

a comparator for comparing a feedback voltage drawn from the feedback node with a reference voltage, to produce a control signal; and

a second transistor controlled by the control signal, for determining to connect a supply voltage to the feedback node to charge the bootstrap capacitor;

wherein the comparator is a hysteretic comparator.