Using isolated supplies instead of bootstrap

Designing with GaN FETs and ICs
1

Good afternoon,

I am working on an academic board similar to the EPC90154. However, as my design requieres no additional heat sources on the PCB from the Qs and the driver, I can not use a bootstrap circuit. Is there any issue that could arise in GaN when using isolated power supplies for the HS and LS?

PowerStage
PowerStage1172×354 73.5 KB

Best regards,

José Miguel.

2

Hello José.
You can use a floating supply, but I recommend to:

  • implement or choose a low input to output capacitance DC/DC (few pF at most) that has been designed specifically for gate drive power supplies, so able to withstand high dV/dt on the output
  • output must be regulated to 5V±5%. Due to the small gate drive power consumption, also a linear regulator (LDO) can be usually used.

The selected gate driver has an internal bootstrap circuit, so there might be a current path from the floating supply to the low side VCC node. Other gate drivers with external bootstrap diodes might be removing this risk, i.e. LMG1210, or any of the galvanically isolated ones. You can have a look here for the supported gate drivers: https://epc-co.com/epc/products/gan-drivers-and-controllers

Regards