The TPS54388C-Q1 device has an integrated boot regulator and requires a small ceramic capacitor between the BOOT and PH pins to provide the gate-drive voltage for the high-side MOSFET. The value of the ceramic capacitor should be 0.1 μF. TI recommends a ceramic capacitor with an X7R- or X5R-grade dielectric with a voltage rating of 10 V or higher because of the stable characteristics over temperature and voltage.

The TPS54388C-Q1 design improves dropout by operating at 100% duty cycle as long as the BOOT-to-PH pin voltage is greater than 2.2 V. A UVLO circuit turns off the high-side MOSFET, allowing for the low-side MOSFET to conduct when the voltage from BOOT to PH drops below 2.2 V. Because the supply current sourced from the BOOT pin is low, the high-side MOSFET can remain on for more switching cycles than are required to refresh the capacitor. Thus, the effective duty cycle of the switching regulator is high.