Microchip says...

"The current datasheets specify Vss-0.3 to Vdd + 0.3v"

"If you start curve tracing the devices you will find that the ESD 
protection diodes
clamp at 0.6v. The 0.3v specification is intended to prevent the input 
protection
diodes from conducting. We have learned that as more analog 
peripherals are
placed on the device, including low power POR/BOR circuits, the 
currents created
when the ESD diodes clamp can cause very bad behavior. In one example, 
the
POR circuit asserted POR when the ESD diodes were conducted. We do not 
want
the ESD diodes conducting so we have specified the voltage range more 
tightly."

__________

At last it's official.
All the things I have kept telling people for years about how not to 
(ab)use protection diodes, and why, are now nicely summed up in an 
official statement.
I can now rest in peace and cease my evangelical campaign against the 
use of protection diodes for use as anything except as protection 
diodes.

Yeah. Right!
Betcha it's business as usual tomorrow.
People will just keep on insisting on their divine right to inject 
arbitary amounts of current into random places inside the IC oblivious 
to the pain and heartbreak it causes the poor old processor and its 
proliferating peripherals.

The fact is, it's always mattered sometimes. And picking which time is 
the time when you care, or whether you can get away with it in a given 
design has always been a matter of luck rather than good design.

Would-be top class engineers will keep right on insisting that you can 
do it safely, and that they've done it for years, and that they have 
37 million devices in the field which are doing it with no bad 
consequences whatsoever.
Walk quietly away, making no sudden moves, with your hands clearly in 
sight.

So.
Just remember.
When you're tempted to say "but it's only a really really little 
current I want to send to its doom down this convenient arbitrary path 
into the heart of my precious program processor" ...
Recall

        "Wafer thin!"


                        Russell


If that doesn't make sense, Gargoyling "wafer thin mint" might. And 
might not.
The result you get by abusing protection diodes may not be as 
spectacular, but it's liable to be even more horrid.




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