Device and method for controlling a buck-boost converter

1. A control circuit to control operation of a buck-boost circuit, the control circuit comprising:

a bootstrap capacitor voltage regulator circuit electrically coupled to a buck-mode bootstrap capacitor of the buck-boost circuit and to a boost-mode bootstrap capacitor of the buck-boost circuit; and

a comparator circuit electrically coupled to the buck-mode bootstrap capacitor and the boost-mode bootstrap capacitor, the comparator circuit configured (i) to control the bootstrap capacitor voltage regulator circuit to maintain a voltage of the buck-mode bootstrap capacitor above a first reference voltage during a boost mode of the buck-boost circuit and (ii) to control the bootstrap capacitor voltage regulator circuit to maintain a voltage of the boost-mode bootstrap capacitor above a second reference voltage during a buck mode of the buck-boost circuit.

2. The control circuit of claim 1 , wherein the bootstrap capacitor voltage regulator circuit comprises:

a first electronic switch having a first terminal electrically coupled to the buck-mode bootstrap capacitor and a second terminal electrically coupled to a first node,

a first diode electrically coupled in parallel with the first electronic switch,

a second electronic switch having a first terminal electrically coupled to the boost-mode bootstrap capacitor and a second terminal electrically coupled to the first node, and

a second diode coupled in parallel with the fourth electronic switch.

3. The control circuit of claim 2 , wherein the comparator circuit is configured to generate switching signals to control the operation of the first electronic switch and the second electronic switch to:

(i) close the first electronic switch and (ii) open the second electronic switch in response to the voltage of the buck-mode bootstrap capacitor being less than the first reference voltage during the boost mode of the buck-boost circuit, and

(i) close the second electronic switch and (ii) open the first electronic switch in response to the voltage of the boost-mode bootstrap capacitor being less than the second reference voltage during the buck-mode of the buck-boost circuit.

4. The control circuit of claim 3 , wherein the comparator circuit comprises:

a first voltage comparator configured to compare the voltage of the buck-mode bootstrap capacitor to the first reference voltage and a first flip-flop to generate a first switching signal to control the first electronic switch, and

a second voltage comparator to compare the voltage of the boost-mode bootstrap capacitor to the second reference voltage and a second flip-flop to generate a second switching signal to control the second electronic switch.

5. The control circuit of claim 2 , wherein the bootstrap capacitor voltage regulator circuit further comprises:

a third diode having an anode coupled to a power supply voltage and a cathode coupled to the first terminal of the third electronic switch, and

a fourth diode having an anode coupled to the power supply voltage and a cathode coupled to the first terminal of the fourth electronic switch.

6. The control circuit of claim 2 , wherein the first electronic switch and the second electronic switch are metal-oxide-semiconductor field effect transistors (MOSFETs), the first diode is a body diode of the third electronic switch, and the second diode is a body diode of the fourth electronic switch.

7. The control circuit of claim 6 , wherein the first terminal of the first electronic switch is a drain terminal and the second terminal of the first electronic switch is a source terminal, and

wherein the first terminal of the second electronic switch is a drain terminal and the second terminal of the second electronic switch is a source terminal.

8. The control circuit of claim 2 , wherein:

the first diode comprises an anode electrically coupled to the first terminal of the first electronic switch and a cathode coupled to the first node, and

the second diode comprises an anode electrically coupled to the first terminal of the second electronic switch and a cathode coupled to the third node.

9. The control circuit of claim 1 , wherein the comparator circuit is configured to:

sense the voltage of the buck-mode bootstrap capacitor and, in response to the voltage of the buck-mode bootstrap capacitor being less than the first reference voltage, control the bootstrap capacitor voltage regulator circuit to transfer an amount of energy from the boost-mode bootstrap capacitor to the buck-mode bootstrap capacitor during the boost mode of the buck-boost converter, and

sense the voltage of the boost-mode bootstrap capacitor and, in response to the voltage of the boost-mode bootstrap capacitor being less than the second reference voltage, control the bootstrap capacitor voltage regulator circuit to transfer an amount of energy from the buck-mode bootstrap capacitor to the boost-mode bootstrap capacitor during the buck mode of the buck-boost converter.

10. The control circuit of claim 9 , wherein the second reference voltage is different from the first reference voltage.

11. A method for controlling the operation of a buck-boost circuit to convert an input voltage to an output voltage, the buck-boost circuit including a buck-mode bootstrap capacitor and a boost-mode bootstrap capacitor, the method comprising:

sensing a voltage of the buck-mode bootstrap capacitor;

sensing a voltage of the boost-mode bootstrap capacitor;

transferring an amount of energy from the boost-mode bootstrap capacitor to the buck-mode bootstrap capacitor in response to (i) the sensed voltage of the buck-mode bootstrap capacitor being less than a first reference voltage and (ii) the buck-boost converter operating in a boost mode, and

transferring an amount of energy from the buck-mode bootstrap capacitor to the boost-mode bootstrap capacitor in response to (i) the voltage of the boost-mode bootstrap capacitor being less than a second reference voltage and (ii) the buck-boost converter operating in a buck mode.

12. The method of claim 11 , wherein:

transferring an amount of energy from the boost-mode bootstrap capacitor to the buck-mode bootstrap capacitor comprises controlling the operation of a first electronic switch to electrically couple the boost-mode bootstrap capacitor to the buck-mode bootstrap capacitor, and

transferring an amount of energy from the buck-mode bootstrap capacitor to the boost-mode bootstrap capacitor comprises controlling the operation of a second electric switch to electrically couple the buck-mode bootstrap capacitor to the boost-mode bootstrap capacitor.

13. The method of claim 12 , wherein:

controlling the operation of the first electronic switch comprises closing the third electronic switch in sync with the boost mode of the buck-boost converter, and

controlling the operation of the second electronic switch comprises closing the fourth electronic switch in sync with the buck mode of the buck-boost converter.

14. The method of claim 12 , wherein:

controlling the operation of the first electronic switch comprises closing the first electronic switch to transfer the amount of energy from the boost-mode bootstrap capacitor to the buck-mode bootstrap capacitor via the first electronic switch and a body diode of the second electronic switch, and

controlling the operation of the second electronic switch comprises closing the second electronic switch to transfer the amount of energy from buck-mode bootstrap capacitor to the boost-mode bootstrap capacitor via the second electronic switch and a body diode of the first electronic switch.

15. The method of claim 11 , wherein the first reference voltage is substantially equal to the second reference voltage.

16. A converter comprising:

an H-bridge buck-boost converter circuit comprising (i) a high-side buck-mode switch, low-side buck-mode switch, and a buck-mode bootstrap capacitor electrically coupled to the high-side buck-mode switch and the low-side buck-mode switch and (ii) a high-side boost-mode switch, a low-side boost-mode switch, and a boost-mode bootstrap capacitor electrically coupled to the high-side boost-mode switch and the low-side boost-mode switch; and

a control circuit electrically coupled to the H-bridge buck-boost converter circuit to maintain a voltage of the buck-mode bootstrap capacitor above a first reference voltage during a boost mode of operation of the H-bridge buck-boost converter circuit and maintain a voltage of the boost-mode bootstrap capacitor above a second reference voltage during a buck mode of operation of the H-bridge buck-boost converter circuit.

17. The converter of claim 16 , wherein the control circuit is configured to:

maintain the voltage of the buck-mode bootstrap capacitor by transferring an amount of energy from the boost-mode bootstrap capacitor to the buck-mode bootstrap capacitor in response to the voltage of the buck-mode bootstrap capacitor being below the first reference voltage, and

maintain the voltage of the boost-mode bootstrap capacitor by transferring an amount of energy from the buck-mode bootstrap capacitor to the boost-mode bootstrap capacitor in response to the voltage of the boost-mode bootstrap capacitor being below the second reference voltage.

18. The converter of claim 16 , wherein the control circuit comprises

a bootstrap capacitor voltage regulator circuit having a first output electrically coupled to the buck-mode bootstrap capacitor and a second output electrically coupled to the boost-mode bootstrap capacitor; and

a voltage comparator circuit electrically coupled to the H-bridge buck-boost converter circuit and the bootstrap capacitor voltage regulator circuit to:

sense the voltage of the buck-mode bootstrap capacitor and, in response to the voltage of the buck-mode bootstrap capacitor being less than the first reference voltage, control the bootstrap capacitor voltage regulator circuit to transfer an amount of energy from the boost-mode bootstrap capacitor to the buck-mode bootstrap capacitor during the boost mode of operation of the buck-boost converter, and

sense the voltage of the boost-mode bootstrap capacitor and, in response to the voltage of the boost-mode bootstrap capacitor being less than the second reference voltage, control the bootstrap capacitor voltage regulator circuit to transfer an amount of energy from the buck-mode bootstrap capacitor to the boost-mode bootstrap capacitor during the buck mode of operation of the buck-boost converter.

19. An electronic device comprising:

a power supply circuit configured to generate a supply voltage;

a converter electrically coupled to the power supply to convert the supply voltage to a converted supply voltage having a voltage magnitude different from the supply voltage, the converter comprising (i) a buck-boost converter circuit including a buck-mode bootstrap capacitor and a boost-mode bootstrap capacitor and (ii) a control circuit electrically coupled to the buck-boost converter circuit to maintain a voltage of the buck-mode bootstrap capacitor above a first reference voltage during a boost mode of the buck-boost converter circuit and maintain a voltage of the boost-mode bootstrap capacitor above a second reference voltage during a buck mode of the buck-boost converter circuit; and

an electronic circuit having an input electrically coupled to the converter to receive the converted supply voltage.

20. The electronic device of claim 19 , wherein the control circuit is configured to:

maintain the voltage of the buck-mode bootstrap capacitor by transferring an amount of energy from the boost-mode bootstrap capacitor to the buck-mode bootstrap capacitor, and

maintain the voltage of the boost-mode bootstrap capacitor by transferring an amount of energy from the buck-mode bootstrap capacitor to the boost-mode bootstrap capacitor.