Using an isolated power supply to power the high-side device has the advantage that it works regardless of continued power-stage switching or duty cycle. Using an isolated power supply can also power the high-side device before power-stage switching begins, eliminating the power-loss concern of switching with an unpowered LMG3522R030-Q1 (see Start-Up and Slew Rate With Bootstrap High-Side Supply for details). Finally, a properly-selected isolated supply introduces less parasitics and reduces noise coupling.

The isolated supply can be obtained with a push-pull converter, a flyback converter, a FlyBuck™ converter, or an isolated power module. When using an unregulated supply, the input of LMG3522R030-Q1 must not exceed the maximum supply voltage. A 16-V TVS diode can be used to clamp the VDD voltage of LMG3522R030-Q1 for additional protection. Minimizing the inter-winding capacitance of the isolated power supply or transformer is necessary to reduce switching loss in hard-switched applications. Furthermore, capacitance across the isolated bias supply inject high currents into the signal-ground of the LMG3522R030-Q1 and can cause problematic ground-bounce transients. A common-mode choke can alleviate most of these issues.