Trickle charge control

1. A system comprising:

a trickle charge control circuit coupled to a charge pump and a motor driver circuit, configured to:

sense a voltage at a bootstrap capacitor voltage node (VBST) of the motor driver circuit;

as a result of the voltage at VBST being greater than a voltage at an input voltage node (VIN), couple a charge pump voltage node (VCP) to VBST of the motor driver circuit, wherein a voltage at VCP is greater than the voltage at VIN; and

as a result of the voltage at VBST being less than the voltage at VIN, decouple VCP from the charge pump from VBST of the motor driver circuit;

wherein the trickle charge control circuit further comprises:

an n-type MOSFET comprising a source coupled to ground, a drain, and a gate;

a first p-type MOSFET comprising a drain coupled to VBST, a source coupled to ground via a resistor and to the gate of the first n-type MOSFET, and a gate coupled to VIN;

a second p-type MOSFET comprising a source coupled to VCP, a drain coupled to VBST, and a gate coupled to the drain of the first n-type MOSFET; and

a resistor coupled to VCP and the gate of the second p-type MOSFET.

2. A system comprising:

a motor driver circuit coupled to an input voltage node (VIN) coupled to a first voltage source, the motor driver circuit comprising:

a switched voltage phase node (VSW);

a high-side metal-oxide-semiconductor field-effect transistor (MOSFET) coupled between VIN and VSW;

a low-side MOSFET coupled between VSW and ground;

a bootstrap capacitor coupled between a bootstrap capacitor voltage node (VBST) and VSW, wherein VBST is coupled to a second voltage source by way of a diode; and

a gate driver to apply either a voltage at VBST or a voltage at VSW to a gate of the high-side MOSFET;

a charge pump coupled to VIN and configured to generate a voltage at a charge pump voltage node (VCP), wherein a voltage at VCP is greater than a voltage at VIN; and

a trickle charge control circuit coupled to the charge pump and the motor driver circuit, configured to:

sense the voltage at VBST;

as a result of the voltage at VBST being greater than the voltage at VIN, couple VCP from the charge pump to VBST of the motor driver circuit; and

as a result of the voltage at VBST being less than the voltage at VIN, decouple VCP from the charge pump from VBST of the motor driver circuit.

3. The system of claim 2 wherein the trickle charge control circuit further comprises:

an inverter having a high output of VCP and a low output of VIN;

a first p-type MOSFET comprising a drain coupled to VBST, a source coupled to an input of the inverter, and a gate coupled to VIN; and

a second p-type MOSFET comprising a source coupled to VCP, a drain coupled to VBST, and a gate coupled to an output of the inverter.

4. The system of claim 2 wherein the trickle charge control circuit further comprises:

an n-type MOSFET comprising a source coupled to VIN, a drain, and a gate;

a first p-type MOSFET comprising a drain coupled to VBST, a source coupled to VIN via a resistor and to the gate of the first n-type MOSFET, and a gate coupled to VIN;

a second p-type MOSFET comprising a drain coupled to VCP, a source coupled to VBST, and a gate coupled to the drain of the first n-type MOSFET; and

a resistor coupled to VCP and the gate of the second p-type MOSFET.

5. The system of claim 2 wherein the trickle charge control circuit further comprises:

an n-type MOSFET comprising a source coupled to ground, a drain, and a gate;

a first p-type MOSFET comprising a drain coupled to VBST, a source coupled to ground via a resistor and to the gate of the first n-type MOSFET, and a gate coupled to VIN;

a second p-type MOSFET comprising a source coupled to VCP, a drain coupled to VBST, and a gate coupled to the drain of the first n-type MOSFET; and

a resistor coupled to VCP and the gate of the second p-type MOSFET.

6. The system of claim 2 wherein the trickle charge control circuit further comprises:

an inverter having a high output of VCP and a low output of VIN;

a diode comprising an anode coupled to VBST and a cathode coupled to VIN via a resistor and to an input of the inverter;

a p-type MOSFET comprising a source coupled to VCP, a drain coupled to VBST, and a gate coupled to an output of the inverter.

7. The system of claim 2 wherein the trickle charge control circuit further comprises:

an n-type MOSFET comprising a source coupled to VIN, a drain, and a gate;

a diode comprising an anode coupled to VBST and a cathode coupled to VIN via a resistor and to the gate of the n-type MOSFET;

a p-type MOSFET comprising a source coupled to VCP, a drain coupled to VBST, and a gate coupled to the drain of the first n-type MOSFET; and

a resistor coupled to VCP and the gate of the p-type MOSFET.

8. A system comprising:

only one charge pump coupled to an input voltage node (VIN) coupled to a first voltage source and configured to generate a voltage at a charge pump voltage node (VCP), wherein a voltage at VCP is greater than a voltage at VIN;

a plurality of motor driver circuits coupled to VIN, each motor driver circuit comprising:

a switched voltage phase node (VSW);

a high-side metal-oxide-semiconductor field-effect transistor (MOSFET) coupled between VIN and VSW;

a low-side MOSFET coupled between VSW and ground;

a bootstrap capacitor coupled between a bootstrap capacitor voltage node (VBST) and VSW, wherein VBST is coupled to a second voltage source by way of a diode; and

a gate driver to apply either a voltage at VBST or a voltage at VSW to a gate of the high-side MOSFET; and

for each of the motor driver circuits, an associated trickle charge control circuit coupled to the charge pump and its associated motor driver circuit, configured to:

sense the voltage at VBST of the associated motor driver circuit;

as a result of the voltage at VBST being greater than the voltage at VIN, couple VCP from the charge pump to VBST of the associated motor driver circuit; and

as a result of the voltage at VBST being less than the voltage at VIN, decouple VCP from the charge pump from VBST of the associated motor driver circuit.

9. The system of claim 8 wherein the trickle charge control circuit further comprises:

an inverter having a high output of VCP and a low output of VIN;

a first p-type MOSFET comprising a drain coupled to VBST, a source coupled to an input of the inverter, and a gate coupled to VIN; and

a second p-type MOSFET comprising a source coupled to VCP, a drain coupled to VBST, and a gate coupled to an output of the inverter.

10. The system of claim 8 wherein the trickle charge control circuit further comprises:

an n-type MOSFET comprising a source coupled to VIN, a drain, and a gate;

a first p-type MOSFET comprising a drain coupled to VBST, a source coupled to VIN via a resistor and to the gate of the first n-type MOSFET, and a gate coupled to VIN;

a second p-type MOSFET comprising a source coupled to VCP, a drain coupled to VBST, and a gate coupled to the drain of the first n-type MOSFET; and

a resistor coupled to VCP and the gate of the second p-type MOSFET.

11. The system of claim 8 wherein the trickle charge control circuit further comprises:

an n-type MOSFET comprising a source coupled to ground, a drain, and a gate;

a first p-type MOSFET comprising a drain coupled to VBST, a source coupled to ground via a resistor and to the gate of the first n-type MOSFET, and a gate coupled to VIN;

a second p-type MOSFET comprising a source coupled to VCP, a drain coupled to VBST, and a gate coupled to the drain of the first n-type MOSFET; and

a resistor coupled to VCP and the gate of the second p-type MOSFET.

12. The system of claim 8 wherein the trickle charge control circuit further comprises:

an inverter having a high output of VCP and a low output of VIN;

a diode comprising an anode coupled to VBST and a cathode coupled to VIN via a resistor and to an input of the inverter;

a p-type MOSFET comprising a source coupled to VCP, a drain coupled to VBST, and a gate coupled to an output of the inverter.

13. The system of claim 8 wherein the trickle charge control circuit further comprises:

an n-type MOSFET comprising a source coupled to VIN, a drain, and a gate;

a diode comprising an anode coupled to VBST and a cathode coupled to VIN via a resistor and to the gate of the n-type MOSFET;

a p-type MOSFET comprising a source coupled to VCP, a drain coupled to VBST, and a gate coupled to the drain of the first n-type MOSFET; and

a resistor coupled to VCP and the gate of the p-type MOSFET.