The TPS54618C-Q1 has an integrated boot regulator and requires a small ceramic capacitor between the BOOT and PH pin to provide the gate drive voltage for the high-side MOSFET. The value of the ceramic capacitor must be 0.1 μF. A ceramic capacitor with an X7R or X5R grade dielectric with a voltage rating of 10 V or higher is recommended because of the stable characteristics over temperature and voltage.

To improve dropout, the TPS54618C-Q1 is designed to operate at 100% duty cycle as long as the BOOT-to-PH pin voltage is greater than 2.2 V. The high-side MOSFET is turned off using a UVLO circuit, 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 very 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 very high.