Hi all,
I am using a MasterGaN5 to drive an electro-optic crystal. The switching rate is variable and can go up to 1-2 MHz, while at times I need to apply a constant high voltage to the crystal. My solution was to use an external isolated 5.5V supply to keep the "Boot" pin at 5.5V above the "Outb" pin. Is it ok to use an external supply like this in place of the bootstrap diode?
I've had issues with the MasterGaN5 failing. Sometimes when it fails it will still turn on, but the rise time is long: 15-20 us. Sometimes it fails where the output will be drift around at some voltage between the HV rail and ground.
The crystal load and associated cables are approximately 120 pF with very little leakage. I have 470 ohms of series resistance to lengthen the rise time seen by the cables and the crystal. I use 5V for Vcc and PVcc, and have attempted to follow the various eval boards and reference designs.
Attached is an excerpt from the schematic (nothing proprietary) and one time I caught a failure on an oscilloscope. In this image, ch2 (purple) is the HV rail at 416V, and it starts drooping when the high switch is turned on, and seems to stabilize after about 1 us when I believe the MasterGaN5 fails. Ch3 (cyan) is the output (after the series resistor). The output voltage never reached the HV rail. Prior to this scope image, it did work for a little. I believe that this problem is worse at higher voltages, I had just increased the HV rail when it failed.
I really appreciate any help solving this problem.
Thanks!
Thomas
