There is a 5V voltage regulator inside the part used to supply external loads, such as digital isolators for the high-side drive signal. The digital outputs of the part use this rail as their supply. No capacitor is required for stability, but transient response is poor if no external capacitor is provided. If the application uses this rail to supply external circuits, TI recommends to have a capacitor of at least 0.1μF for improved transient response. A larger capacitor can be used for further transient response improvement. The decoupling capacitor used here must be a low-ESR ceramic type. Capacitances above 0.47μF will slow down the start-up time of the LMG342xR030 due to the ramp-up time of the 5V rail.