I have an application where I am high-side switching several 65V 1A=20
loads from a microcontroller, using P Channel mosfets.  For various=20
reasons I am stuck with the P channel mosfets as the output devices -=20
mostly because I need to slow the turnon and turnoff of the FET's to=20
round the turnon/turnoff waveform to avoid an inductive spike in nearby=20
wiring by the quick turnon or turnoff.

In any case, I also need to short-circuit protect these devices.   I=20
keep running into issues when trying to do this:

1) PTC's don't seem to be the right tool for this job.   Yes, they seem=20
to work, but only 'mostly ok'.  I can go into more details if necessary.

2) I would love to do this in software in the microcontroller, using a=20
high-side 'current sense amplifier', but I have yet to find a high side=20
current sense amplifier which is both reasonable in cost (dollar or less=20
@ QTY 1K), and works on both 3.3V on the ADC side, and 65V on the 'high=20
side current sense' side.

3) I swear I have seen a simple, elegant, current limiting circuit which=20
uses a MOSFET and a few external components - but alas no luck yet.

Does anyone have any ideas or pointers for somewhere I haven't looked yet?

-forrest
--=20
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