Is there a rule of thumb for selecting Schottky diode to accompany the GaN FET?
A small parallel Schottky diode can be put in parallel to the bottom FET in a half-bridge topology.
The reasons for these diodes:
- prevent switch node going too low. If it goes too low, there is the potential of the controller (or driver) latching up.
- prevent the negative voltage causing the boost voltage going too high.
Some data sheet recommends this even for Silicon MOSFETs, but usually for a different reason: the reverse recovery problem of silicon MOSFETs.
The main criteria to consider in the selection are:
• Average current can be low: the diode conducts usually only during the deadtime (but be careful with special conditions depending on your application). We usually use 1A or 2A rate diodes
• Peak current should be high: it will limit how small a diode can be used, as the diode conducts full current, even if just during deadtime
• low capacitance: the smaller the better, as this capacitance is added to Coss losses
• low voltage drop…of course
I hope this helps!
Yes good guidance, so 2A but more important surge rating and VRRM to match GaN FET.