Boost and up-down switching regulator with synchronous freewheeling MOSFET

• US 20090010035A1
• Filed: 04/21/2008
• Published: 01/08/2009
• Est. Priority Date: 07/06/2007
• Status: Active Grant

• Current Assignee: Advanced Analogic Technologies Incorporated (Skyworks Solutions Incorporated)
• Original Assignee: Advanced Analogic Technologies Incorporated (Skyworks Solutions Incorporated)
• Inventors: Williams, Richard K.
• Granted Patent: US 7,977,926 B2
• Time in Patent Office: Days
• US Class Current: 363/131
• CPC Class Codes: H02M 3/158 including plural semiconductor devices as final control devices for a single load
• CPC Class Codes: H02M 3/1582 Buck-boost converters H02M3/1584 takes precedence

Abstract

A freewheeling MOSFET is connected in parallel with the inductor in a switched DC/DC converter. When the freewheeling MOSFET is turned on during the switching operation of the converter, while the low-side and energy transfer MOSFETs are turned off, the inductor current circulates or “freewheels” through the freewheeling MOSFET. The frequency of the converter is thereby made independent of the lengths of the magnetizing and energy transfer stages, allowing far greater flexibility in operating and converter and overcoming numerous problems associated with conventional DC/DC converters. For example, the converter may operate in either step-up or step-down mode and may even transition for one mode to the other as the values of the input voltage and desired output voltage vary.

Claims

1. A DC/DC converter comprising:

an inductor and a low-side switch connected in a series conduction path between first and second supply voltages, the inductor being coupled to the first supply voltage and the low-side switch being coupled to the second supply voltage, a V_x node being located in the series conduction path between the inductor and the low-side switch;

an energy transfer switch connected between the V_x node and an output terminal of the converter; and

a freewheeling switch connected in parallel with the inductor.

2. The DC/DC converter of claim 1 wherein the freewheeling switch comprises a freewheeling MOSFET.

3. The DC/DC converter of claim 2 wherein the freewheeling switch comprises a body bias generator, the body bias generator being coupled to each of the source, drain and body of the freewheeling MOSFET, the body bias generator being adapted to short the body to one of the source and drain of the freewheeling MOSFET responsive to a relationship between voltages present at the source and drain, respectively, of the freewheeling MOSFET so as to prevent any P-N junction in the freewheeling MOSFET from becoming forward-biased.

4. The DC/DC converter of claim 3 wherein the body bias generator comprises a first body bias MOSFET coupled between the body and the drain of the freewheeling MOSFET and a second body bias MOSFET coupled between the body and the source of the freewheeling MOSFET, a gate of the first body bias MOSFET being coupled to the source of the freewheeling MOSFET, and a gate of the second body bias MOSFET being coupled to the drain of the freewheeling MOSFET.

5. The DC/DC converter of claim 2 comprising a voltage clamping circuit connected in parallel with the freewheeling MOSFET, the voltage clamping circuit comprising a clamping diode connected in series with a clamping switch.

6. The DC/DC converter of claim 5 wherein the voltage clamping circuit comprises a blocking diode connected in series with the clamping diode and in parallel with the clamping switch, the blocking diode and the clamping diode being oriented so as to oppose a flow of current in either direction in a series path comprising the blocking diode and the clamping diode.

7. The DC/DC converter of claim 6 wherein the clamping switch comprises a clamping MOSFET and further comprising a gate drive circuit coupled to a gate of the clamping MOSFET, the gate drive circuit adapted to control the gate of the clamping MOSFET in response to a relationship between the first supply voltage and a voltage at the output terminal.

8. The DC/DC converter of claim 2 wherein the energy transfer switch comprises an energy transfer MOSFET.

9. The DC/DC converter of claim 8 wherein the energy transfer switch comprises a body bias generator, the body bias generator being coupled to each of the source, drain and body of the energy transfer MOSFET, the body bias generator being adapted to short the body to one of the source and drain of the energy transfer MOSFET responsive to a relationship between voltages present at the source and drain, respectively, of the energy transfer MOSFET so as to prevent any P-N junction in the energy transfer MOSFET from becoming forward-biased.

10. The DC/DC converter of claim 9 wherein the body bias generator comprises a first body bias MOSFET coupled between the body and the drain of the energy transfer MOSFET and a second body bias MOSFET coupled between the body and the source of the energy transfer MOSFET, a gate of the first body bias MOSFET being coupled to the source of the energy transfer MOSFET, and a gate of the second body bias MOSFET being coupled to the drain of the energy transfer MOSFET.

11. The DC/DC converter of claim 10 comprising a voltage clamping circuit connected in parallel with the energy transfer MOSFET, the voltage clamping circuit comprising a clamping diode connected in series with a clamping switch.

12. The DC/DC converter of claim 11 wherein the voltage clamping circuit comprises a blocking diode connected in series with the clamping diode and in parallel with the clamping switch, the blocking diode and the clamping diode being oriented so as to oppose a flow of current in either direction in a series path comprising the blocking diode and the clamping diode.

13. The DC/DC converter of claim 12 wherein the clamping switch comprises a clamping MOSFET and further comprising a gate drive circuit coupled to a gate of the clamping MOSFET, the gate drive circuit adapted to control the gate of the clamping MOSFET in response to a relationship between the first supply voltage and a voltage at the output terminal.

14. The DC/DC converter of claim 8 wherein a body of the energy transfer MOSFET is connected to a body bias voltage such that a source/body junction or a drain/body junction in the energy transfer MOSFET is not forward-biased during the normal operation of the converter.

15. The DC/DC converter of claim 14 wherein the body bias voltage is equal to the second supply voltage.

16. The DC/DC converter of claim 2 wherein a body of the freewheeling MOSFET is connected to a body bias voltage such that a source/body junction or a drain/body junction in the freewheeling MOSFET is not forward-biased during the normal operation of the converter.

17. The DC/DC converter of claim 16 wherein the body bias voltage is equal to the second supply voltage.

18. The DC/DC converter of claim 1 comprising a clamping diode connected between the V_x node and an adaptive clamping circuit, the adaptive clamping circuit being adapted to connect the diode to either the first supply voltage or a voltage at the output terminal depending on a relationship between the first supply voltage and a voltage at the output terminal.

19. A DC/DC converter comprising:

an inductor and a low-side switch connected in a series conduction path between first and second supply voltages, the inductor being coupled to the first supply voltage and the low-side switch being coupled to the second supply voltage, a V_x node being located in the series conduction path between the inductor and the low-side switch;

an energy transfer diode connected between the V_x node and an output terminal of the converter; and

a freewheeling switch connected in parallel with the inductor.

20. A method of converting a DC input voltage to a DC output voltage comprising:

applying the DC input voltage to a first terminal of an inductor while coupling a second terminal of the inductor to a circuit ground so as to magnetize the inductor;

disconnecting the second terminal of the inductor from the circuit ground;

coupling the second terminal of the inductor to a capacitor and an output terminal so as to provide the DC output voltage at the output terminal;

disconnecting the second terminal of the inductor from the capacitor and the output terminal; and

connecting the first and second terminals of the inductor together while the second terminal of the inductor is disconnected from the capacitor and the output terminal.

21. The method of claim 20 comprising:

providing a first break-before-make interval between disconnecting the second terminal of the inductor from circuit ground and coupling the second terminal of the inductor to the capacitor and the output terminal; and

limiting a rise in a voltage at the second terminal of the inductor during the first break-before-make interval.

22. The method of claim 21 comprising:

providing a second break-before-make interval between disconnecting the second terminal of the inductor from the capacitor and the output terminal and connecting the first and second terminals of the inductor together; and

limiting a rise in a voltage at the second terminal of the inductor during the second break-before-make interval.

23. The method of claim 20 wherein the DC output voltage is higher than the DC input voltage.

24. The method of claim 20 wherein the DC output voltage is lower than the DC input voltage.

25. The method of claim 20 wherein connecting the first and second terminals of the inductor together comprises:

connecting a freewheeling MOSFET between the first and second terminals of the inductor; and

turning the freewheeling MOSFET on.

26. The method of claim 25 comprising controlling the voltage of a body of the freewheeling MOSFET so as to prevent any P-N junction in the freewheeling MOSFET from becoming forward-biased.

27. The method of claim 20 wherein coupling the second terminal of the inductor to a capacitor and an output terminal comprises:

connecting an energy transfer MOSFET between the second terminal of the inductor and the capacitor and the output terminal; and

turning the energy transfer MOSFET on.

28. The method of claim 27 comprising controlling the voltage of a body of the energy transfer MOSFET so as to prevent any P-N junction in the energy transfer MOSFET from becoming forward-biased.

29. A method of starting a DC/DC converter, the DC/DC converter comprising an inductor and a capacitor, the method comprising connecting an input voltage to the inductor and shunting a current around the inductor so as to pre-charge the capacitor to a predetermined voltage.

30. The method of claim 29 wherein the predetermined voltage is higher than the input voltage.

31. The method of claim 29 wherein the predetermined voltage is lower than the input voltage.