The high-side N-type MOSFET in an external powerstage requires about 10-V higher than the motor voltage to fully enhance the MOSFET. In some applications, this FET needs to be on for the entire PWM period (100% duty cycle support), which presents challenges in design to provide a regulated gate voltage and gate current. TI provides two choices of integration to support 100% duty cycle for high-side MOSFET enhancement: bootstrap or charge pump architectures.

Bootstrap architectures use external bootstrap capacitors to provide high-side MOSFET enhancement from an externally provided or internally generated gate drive voltage (GVDD). In order to refresh the bootstrap capacitors, the high-side FET must be switched off and the low-side FET must be switched on for a minimum amount of time. To support 100% duty cycle, a trickle charge pump is integrated into the device to keep the high-side MOSFET enhanced. Bootstrap architectures are low-cost, small in integration, and have high efficiency.

Charge pump architectures integrate a doubler or tripler charge pump controller to regulate the high-side gate drive voltage from the motor driver supply voltage. This eliminates the need for external bootstrap capacitors and requires only two capacitors for charge pump operation. A doubler or tripler charge pump allows for lower minimum supply voltage requirements to generate the high-side MOSFET gate drive voltage.