The bootstrap capacitor provides the gate charge for the high-side switch, DC bias power for HB undervoltage lockout circuit, and the reverse recovery charge of the bootstrap diode. The required bypass capacitance can be calculated with Equation 2.

where

• I_HB is the quiescent current of the high-side driver
• T_on is the maximum on-time period of the high-side transistor
• I_GSS is the gate leakage current of the high-side transistor

A good-quality ceramic capacitor must be used for the bootstrap capacitor. TI recommends placing the bootstrap capacitor as close as possible to the HB and HS pins.