RussellMc wrote:
> An interesting perspective.
> I believe you'll find that the glass is half full.
> I'm not sure why you'd think that being surprised when something dies
> AND not expecting to be able to violate the data sheet spec with
> impunity are mutually incompatible.
>
> Using a more familiar topic as an example.:
>
> Many processors specifiy maximum signal excursion on input pins to be
> not more than 0.2V or 0.3V outside power supply rails. Some processors
> specify 0V tolerance. On a 0V tolerance part I'd be surprised if an
> excursion of up to say 0.2V  outside the power rails would cause
> damage or mis-operation. BUT, if it did I'd know that I had no
> comeback, and I'd seek to design related circuitry so that the 0V
> tolerance was met.
> I'd guess that the reason for the <0.2 or < 0.3 Volt specification was
> due to these voltages being << the forward voltage of the protection
> diodes. I'd assume that the IC was designed and built as above,  and
> be surprised if it wasn't, but know that if my assumptions were wrong
> I'd have no 'comeback'.

I'm not sure what your point is.  I agree with what you're saying, but how
does that apply to 12V on MCLR when the absolute maximum rating is 6V?
That's way beyond the rating, not just less than a diode drop so nothing ba=
d
will probably happen, most of the time.

I'm guessing that on the 3.3V only parts, MCLR does have a protection diode
like the other pins.  Raising it to 12V therefore effectively applies over
11V Vdd to at least part of the chip.  That is so far outside spec it is
very likely to cause damage.  Whether the excess current blows the
protection diode or the excess voltage blows up the rest of the chip I
wouldn't guess on.  Either way the chip is damaged.


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