danadak wrote:You might consider 4 mods -
Erk! These would have been easier a day or so ago!
1) Use of a RRIO OpAmp vs a LM358, to increase drive level to MOSFET. Make
sure your choice can handle large C load, eg. stability reasons. Design wise
insure power sequencing in this circuit cannot cause phase reversal of the
OpAmp outputs. Stated another way make sure OpAmp power supply comes
up before any other pin on the OpAmp.
I based the design on that used in the Arduino and the Eleven. As long as its output is over the mosfet's threshold, though, it should work fine, no? I presume that it does, since it's widely used elsewhere.
2) For 3.3V Regulator, strap a diode across it to prevent blowing out reg if
its input is shorted to ground, caused by its output cap C18 discharging back
thru regulator. That would be D1 in this example.
Fair point. I'll fix that for the next revision.
3) Some place on board edge for a large ground post where scope probe ground
clips can be placed w/o shorting any other part of board.
Also a fair point. I think the mounting holes ought to be shorted to ground, but a better place for this wouldn't hurt.
4) Use polymer tanatalums in BOM for any bulk caps, they have ~ 10 x better
freq response curves than regular tantalums, lower noise in board.
For the switching regulator and the linear regulator, I've used the caps recommended in their datasheets and by the TI designer. For the decoupling caps on the MPU, I've used standard ceramics, but I don't think that's what you had in mind by bulk caps. I don't think that leaves any?