Schottky diode selection

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:

  1. prevent switch node going too low. If it goes too low, there is the potential of the controller (or driver) latching up.
  2. 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.