Using an isolated power supply to power the high-side device has the advantage that it will work regardless of continued GaN device switching or duty cycle. It can also power the high-side device before device switching begins, eliminating the power-loss concern of switching with an unpowered LMG341xR150 (see Startup and Slew Rate with Bootstrap High-Side Supply for details). Finally, a properly-selected isolated supply will contribute fewer parasitics to the switching GaN device, increasing design efficiency. However, the isolated power supply solution is larger and more expensive than the bootstrap solution.
The isolated supply can be constructed from an output of a flyback or FlyBuck™ converter, or using an isolated power module. When using an unregulated supply, ensure that the input to the LMG341xR150 does not exceed the maximum supply voltage. If necessary, a 18 V zener to clamp the VDD voltage supplied by the isolated power converter. Minimizing the inter-winding capacitance of the isolated power supply or transformer is necessary to reduce switching loss in hard-switched applications.