The internal bootstrap diode function is implemented with a smart-switched GaN bootstrap FET. The GaN bootstrap FET blocks current in both directions between AUX and BST when the GaN bootstrap FET is turned off.

The bootstrap diode function is active when the low-side GaN power FET is turned on and inactive when the low-side GaN power FET is turned off. The GaN bootstrap FET is held off in the bootstrap diode inactive phase. The GaN bootstrap FET is turned on a single time at the beginning of the bootstrap active phase and is controlled as an ideal diode with diode current flowing from AUX to BST to charge the BST-to-SW capacitor. If a small reverse current from BST to AUX is detected after the GaN bootstrap FET is turned on, the GaN bootstrap FET is turned off for the remainder of the bootstrap active phase.

The bootstrap diode function implements a current limit to protect the GaN bootstrap FET when the BST-to-SW capacitor is significantly discharged at the beginning of the bootstrap active phase. If there is no current limit situation during the GaN bootstrap FET turn on, or if the bootstrap function drops out of current limit as the BST-to-SW capacitor charges, the current limit function is disabled for the remainder of the GaN bootstrap FET turn-on time. The current limit function is disabled to save quiescent current.