Bootstrap clamping circuit for DC/DC regulators and method thereof

• US 7,518,352 B2
• Filed: 05/11/2007
• Issued: 04/14/2009
• Est. Priority Date: 05/11/2007
• Status: Expired due to Fees

• Current Assignee: North Star Innovations Inc. (Wi-LAN Inc.)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: De Lima Filho, Jader Alves, Pimenta, Wallace Alane, Saez, Richard Titov Lara
• Primary Examiner(s): Laxton, Gary L
• Application Number:
  US11/747,414
• Publication Number:
  US 20080278135A1
• Time in Patent Office: 704 Days
• Field of Search: 323/224, 323/265, 323/266, 323/282, 323/284, 323/285, 323/288, 323/351, 327/390, 327/540, 327/541, 327/589
• US Class Current: 323/288
• CPC Class Codes: G05F 1/575 characterised by the feedback circuit
• CPC Class Codes: H02M 1/0006 Arrangements for supplying an adequate voltage to the control circuit of converters
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators
• CPC Class Codes: H03K 17/08122 in field-effect transistor switches

Abstract

A clamping circuit of a DC/DC regulator includes a reference current generator to generate a reference current. The reference current can be based upon a specified maximum voltage across a bootstrap capacitor of the DC/DC regulator. The clamping circuit also includes a current generator that generates a current based on the voltage across the bootstrap capacitor. The current generated by the current generator is compared to the generated reference current. Based on the comparison, the voltage across the bootstrap capacitor is regulated. By regulating the voltage across the bootstrap capacitor based on current, rather than based directly on the voltage across the capacitor, the design of the clamping circuit is simplified compared to voltage-based implementations.

Claims

1. A device, comprising:

a power switch comprising a first terminal coupled to an input voltage, a second terminal, and a control terminal;

a bootstrap capacitor comprising a first terminal coupled to the second terminal of the power switch and a second terminal;

a driver circuit comprising a first terminal coupled to the second terminal of the power switch, a second terminal coupled to the second terminal of the bootstrap capacitor, and an output terminal;

a current reference circuit configured to generate a reference current;

a current generator circuit configured to generate a first current based on a voltage across the bootstrap capacitor; and

a compare circuit comprising an output coupled to the control terminal of the power switch, the output configured to generate a control signal based on a comparison of the reference current and the first current, the control signal to control the conductivity of the power switch.

2. The device of claim 1, wherein the reference current is based on a reference voltage.

3. The device of claim 2, wherein the reference voltage is based on a specified maximum gate-source voltage of a transistor of the DC-DC converter.

4. The device of claim 2, wherein the current reference circuit comprises:

a reference voltage circuit comprising an output to provide the reference voltage;

a first transistor comprising a first current electrode coupled to a first power voltage, a second current electrode, and a control electrode coupled to the output of the reference voltage circuit;

a second transistor comprising a first current electrode, a second current electrode coupled to a first voltage reference, and a control electrode coupled to the first current electrode;

a third transistor comprising a first current electrode to provide the reference current, a second current electrode coupled to the first voltage reference, and a control electrode coupled to the control electrode of the second transistor; and

a set of transistors coupled in series between the second current electrode of the first transistor and the first current electrode of the second transistor.

5. The device of claim 4, wherein the set of transistors comprises a fourth transistor comprising a first current electrode coupled to the second current electrode of the first transistor, a second current electrode, and a control electrode coupled to the first current electrode of the fourth transistor.

6. The device of claim 4, wherein the reference voltage circuit comprises a zener diode comprising a first terminal coupled to the output of the reference voltage circuit and a second terminal coupled to the first voltage reference.

7. The device of claim 6, wherein the reference voltage circuit further comprises a diode coupled in series with the zener diode.

8. The device of claim 4, wherein the current reference circuit further comprises:

a fourth transistor comprising a first current electrode coupled to the power voltage, a second current electrode, and a control electrode coupled to the second current electrode;

a fifth transistor comprising a first current electrode coupled to the power voltage, a second current electrode coupled to the output of the reference voltage circuit, and a control electrode coupled to the control electrode of the fourth transistor; and

a current source comprising a first terminal coupled to the second current electrode of the fourth transistor and a second terminal coupled to the first voltage reference.

9. The device of claim 4, wherein the current reference circuit further comprises a fourth transistor comprising a first current electrode coupled to a second voltage reference, a second current electrode coupled to the first current electrode of the third transistor, and a control electrode coupled to the second current electrode.

10. The device of claim 1, wherein the current reference circuit comprises:

a first transistor comprising a first current electrode coupled to a first voltage node, a second current electrode, and a control electrode coupled to the second current electrode, a voltage at the first voltage node based on a voltage at a first terminal of the bootstrap capacitor;

a second transistor comprising a first current electrode coupled to the boot voltage node, a second current electrode, and a control electrode coupled to the control electrode of the first transistor;

a third transistor comprising a first current electrode coupled to the second current electrode of the first transistor, a second current electrode, and a control electrode coupled to the second current electrode;

a fourth transistor comprising a first current electrode coupled to the second current electrode of the second transistor, a second current electrode to provide the first current, and a control electrode coupled to the control electrode of the third transistor; and

a set of transistors coupled in series between the second current electrode of the third transistor and a second voltage node, a voltage at the second voltage node based on a voltage at a second terminal of the bootstrap capacitor.

11. The device of claim 10, wherein the set of transistors comprises a fifth transistor comprising a first current electrode coupled to the second current electrode of the third transistor, a second current electrode coupled to the second voltage node, and a control electrode coupled to the first current electrode.

12. The device of claim 1, wherein the compare circuit comprises:

a first input to receive a voltage based on the reference current;

a second input to receive a voltage based on the first current;

an output node to provide the control signal;

a first transistor comprising a first current electrode coupled to a first voltage reference, a second current electrode coupled the output node, and a control electrode coupled to the first input; and

a second transistor comprising a first current electrode coupled to the output node, a second current electrode coupled to a second voltage reference, and a control electrode coupled to the second input.

13. The device of claim 1, further comprising a power stage of the DC-DC comprising an input coupled to the output terminal of the driver circuit and an output to provide a voltage based on the input voltage.

14. A method, comprising:

determining a reference current based on a reference voltage;

determining a first current based on a voltage across a bootstrap capacitor; and

controlling application of a power voltage to the bootstrap capacitor of a DC-DC converter based on a comparison of the reference current and the first current.

15. The method of claim 14, further comprising providing the voltage across the bootstrap capacitor to a driver circuit of the DC-DC converter, the driver circuit to control application of the power voltage to a power stage of the DC-DC converter.

16. The method of claim 14, wherein the reference voltage is based on the voltage across a zener diode.

17. The method of claim 16, wherein the reference voltage is further based on the voltage across a diode coupled in series with the zener diode.

18. The method of claim 14, wherein the reference voltage is based on a specified maximum gate-source voltage of a transistor of the DC-DC converter.

19. The method of claim 14, wherein determining the first current comprises:

applying a first voltage to a current electrode of a first transistor, the first voltage based on a voltage at a first terminal of the bootstrap capacitor;

applying a second voltage to a current electrode of a second transistor, the second voltage based on a voltage at a second terminal of the bootstrap capacitor; and

determining the first current based on a difference between the first voltage and the first current.

20. The method of claim 14, further comprising converting the power voltage to an output voltage.