piclist 1999\10\10\194311a >
Thread: Good Design More on (ab)use of PIC protection diodes & bad design
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face BY : Dennis Plunkett email (remove spam text)



At 22:57 9/10/99 +1300, you wrote:
{Quote hidden}

Wow Russ,
Yes you are correct in that the protection diodes are not guarrenteed to
save the device, an any way, they are nominaly included for ESD only! Yes
William is correct with the AC APP note, but this is a side issue! But side
issuee or not this does rasie the question of DO MICROCHIP CONDONE the use
of protection diodes for clamping? It would seem that they do, as the APP
NOTE suggests (I think that you could wave this one at them if a device
fails).
But!
Russ is correct in that this is not good design practice (But try telling
that to the people whem desing for the Automotive market) Getting back to
the original post I have a few questions that undoubtably others have also
considered. The 10uA in whhich direction and to where does this go? into
the core or out the pin? The resets and configuration alterations indicate
that the current spikes are in exccess of the diode nominal capacity, or
that they are causing some EMI into the PIC. I think that this circuit
needs to be investagated and some more answers / questions need to be raised.
But in general I agree with Russ, protection diodes are a bonus only
(typically for ESD not nominal high current rates). Also, need to find out
how fast these diodes are (This is a hint at the EMI problem (Been down
this road with MIL stuff many a time))


Dennis

<3.0.32.19991011084851.006f0dec@huey>

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Subject (change) Good Design More on (ab)use of PIC protection diodes & bad design

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