Wouter van Ooijen <wouter <at> voti.nl> writes:

> If I understand you right: You used a chip outside its specs and it
> worked. You use the newer chip this way and it fails. And you are
> surprised?

That is not what I was saying. What I was saying was, that the spec is lying or
wrong. The actual permitted Vclamp is probably Vdd+0.3V/Vss-0.3V as opposed to
the stated 0.6V. Iow, that chip cannot clamp at all, since its bulk diodes will
never open at +/-0.3V!. Then, clamping with a silicon diode (1N4148) did not fix
the problem, and I had to use Schottky. With the silicon diode I measured -0.59V
or so which is within spec, and the chip still did not work. Worse, more exact
Vclamp specs are not to be found in that datasheet. Of course you realize that
such a chip fitted with standard tranzorbs and suppression networks on IO pins
and connected to a normal circuit can and will be subjected to input voltage
excursions to -0.6V in normal operation (e.g. hum, induced voltage, capacitive
effects, galvanic bias from humidity, ground current etc), where the reverse
conducting tranzorb will 'catch' them, but too late, after they will have caused
a clock loss by the core ? So one would have to use a Schottky tranzorb or
something even more expensive ?

thanks,
Peter P.


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