Bob Blick wrote:
>
> >Not necessarily so.  The structures that sustain the flyback current are
> >not necessarily the same as those that conduct the forward current, and,
> >if sufficient current flows into the substrate, the whole chip can turn
> >in to a thyristor!
>
> I beg to differ. Please check the data sheets, and you will see something
> like this:
>
> "Input clamp current, IOK(VI<0 or VI>VDD).....+-20mA"
>
> I realize that output current is rated at 25mA, but the fact of the matter
> is that PICs have good protection on most of the pins, they are not your
> average CMOS chip.
>
> Cheers, Bob


Agreed that the protection diodes are rated as you state, but I stand by
what I said.  It is not generally true that such diodes can withstand
the SAME current as the output transistors, and the thyristor latch-up
problem is well-documented.
--

Paul Mathews, consulting engineer
AEngineering Co.
optoeng@whidbey.com
non-contact sensing and optoelectronics specialists