Firstly I am wondering what FET was used in this “synchronous bootstrap supply” circuit. Is this a GaN FET or regular MOSFET? And what specific properties of this FET are important for its proper functionality?
How2AppNote015 Ultra thin High Efficiency Multi-level Converters.pdf (epc-co.com)
Additionally, what is the benefit of using a FET here instead of just a traditional bootstrap diode?
Thanks.
Thanks for writing in!
The board referred to in this application note is an early version of a reference design. The released version is EPC9148. Home page for this board: https://epc-co.com/epc/products/evaluation-boards/epc9148
Schematic: https://epc-co.com/epc/Portals/0/epc/documents/schematics/EPC9148_Schematic.pdf
The FET in the synchronous bootstrap supply is a tiny EPC GaN FET, EPC2038. The purpose of the small, optional circuit with EPC2038 is to bypass the PN diode inside the gate driver IC. This FET was selected for: very high speed, 100 V rating, and very small. This circuit may not be necessary, depending on application; usually it becomes more useful above 2 MHz or so. It can make the gate driver more efficient (bypasses the slow PN diode and its reverse recovery, with a GaN FET).
Some other gate drivers have an external bootstrap diode, that gives the option of using a high-speed Schottky diode.
By the way, on the EPC9148 board home page is this video, made with the inductor manufacturer Wurth. I’m the narrator, but I think I didn’t cover your good question… https://youtu.be/guKRP5KbXRU
I hope this helps!