The bootstrap capacitor
biases the high-side gate driver during the high-side FET on-time. TI recommends that a
100-nF capacitor rated for 10 V or higher is used. The VBSTI(UV) threshold is
designed to maintain proper high-side FET switching operation. If the CBST
capacitor voltage drops below VBST(UV), then the device initiates a charging
sequence, turning on the low-side FET before attempting to turn on the high-side FET.
For a very low PWM frequency, the charging sequence is initiated on the rising edge of
the PWM pulse. The duration of the low-side switch turn-on as a function of pulse width
can be tuned by increasing the value of bootstrap capacitor, CBSTI, depending
on the application.