The bootstrap capacitor provides the gate charge for the high-side gate drive, dc bias power for HB UVLO circuit, and the reverse recovery charge of the bootstrap diode. The required bypass capacitance can be calculated using Equation 2.

where

• I_HB is the quiescent current of the high-side gate driver
• t_ON(maximum) is the maximum on-time period of the high-side gate driver
• Q_RR is the reverse recovery charge of the bootstrap diode
• Q_G is the gate charge of the high-side GaN FET
• ΔV is the permissible ripple in the bootstrap capacitor (< 100 mV, typical)

A 0.1-µF, 16-V, 0402 ceramic capacitor is suitable for most applications. Place the bootstrap capacitor as close as possible to the HB and HS pins.