Sourcing bootstrap diodes

[dick_freebird]

Working on an isolating GaN Driver chip design,
I'm discovering a lack of appropriate diodes for
the boostrap role. Part is supposed to do 200V
and options get slim quick, especially as NASA
now wants to derate 50% for Schottky diodes
absent beam line data. Given that I also have a
speed tasking, I think I need ultrafast (not so
desirable for the forward voltage drop) or Schottky.
But Schottky diodes I find in this voltage range are
all pretty high current, high Cj and that Cj*VIN
comes right off the top as switching loss (and high
shuttle peak current).

Something like 400V, 3A peak / <1A steady, sub-nF
Cj (not commonly one of the selection params) is
where I'm centered now.

Any faves, or familes to look at?

 

[crutschow]

What is the frequency that the bootstrap diode sees?

 

[dick_freebird]

Looking to hit 20-30MHz switching (my old product
made 30MHz but that foundry "went away" and the part
with it).

Not ready to go with the third-GaN-FET bootstrap
scheme that's shown up in a driver recently, though
that would fix the Vf drop.

1/2CV^2*f gets pretty ugly at that frequency & voltage.
Maybe we will have to call out different combos of
boot cap and diode (and resistor?) for different VIN,
fSW and FET - seems to be kinda the norm, that the
BOM values around this end up being specific to
those "inputs".

But the challenge is at the big end, in finding the low
Cj, high Vr, fast-as-can-be magical part.

 

[Easy peasy]

This is probably one of the better ones:

https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://semic.cz/!old/files/pdf_www/STTH1R06_ST.pdf&ved=2ahUKEwja66jEpIeIAxV8wzgGHXA7LhwQFnoECBYQAQ&usg=AOvVaw1FPv1VaWPKm84DZ-c7DZEa