10.1 Using an Isolated Power Supply

Using an isolated power supply to power the high-side device has the advantage that it will work regardless of continued power-stage switching or duty cycle. It can also power the high-side device before power-stage switching begins, eliminating the power-loss concern of switching with an unpowered LMG341xR070 (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 power stage, increasing power-stage 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 LMG341xR070 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.