I am in the process of convering several designs for SMD parts for our=20
new P&P machine when It comes in.

For input protection in the past, I've been using either 1n5819 schottky=20
diodes or SP721A SCR/diode arrays for ESD protection - usually with a=20
330 ohm series diode, and then these diodes to the rail.   This has=20
served me remarkably well, but I'd like to reevaluate this with the=20
change to SMD.

It appears I need to select a Vf of my protection diodes, of something=20
less than 0.3V.   Interestingly enough, the 1n5819's I have been using=20
are higher than that - 600mv or higher - and the SP721's are even=20
worse.  Which makes me think that maybe they haven't been serving me=20
that well.  On the other hand, I'm not exactly sure where one would find=20
such a low Vf in a diode....

I also need to be able to clamp the Vdd of the ciruit to no more than=20
3.6V, since I do occasionally have situtions where clamp currents will=20
raise the Vdd above 3.6V, causing permanent issues.   On the other hand,=20
my voltage regulator's maximum output voltage is as high as 3.465V, so=20
really I have to clamp between that and 3.6V, which is pretty tight. =20
And all the 'standard' clamp-type devices (esd suppression diodes,=20
zeners, etc) aren't that tight.

I could clamp the inputs using a 3V0 or 3V3 'zener-like' device, aka a=20
surge suppression diode, but that isn't nearly as useful on outputs that=20
also need to be protected from raises, and has a possible 'vdd' voltage=20
range of more than 0.3V - that is, my regulator is rated from 3.135 to=20
3.465V, across the operating range.

Is there another quick and easy method I'm missing?  Or are there=20
components I'm missing that would work better?  I know I've asked=20
similar questions in the past, but just haven't come up with a good=20
answer yet...

Ideas?

-forrest
--=20
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