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Thread: Good Design More on (ab)use of PIC protection diodes & bad design
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face BY : Jim Hartmann email (remove spam text)



Would you kindly point me to a page and line where it says that a negative
voltage WRT Vss on a pin violates the operating conditions?

Jim Hartmann





Alan Pearce <KILLspamA.B.Pearcespam_OUTspamRL.AC.UK>spam_OUTspamMITVMA.MIT.EDU> on 10/11/1999 09:55:08 AM

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


Connecting a negative voltage to an input pin, even through a resistor
quite
clearly violates the "operating" portion of the data sheet. The "maximum"
portion of the data sheet is conditions that the chip can withstand without
damage, but are definitely not part of the operating conditions. hence the
protection diode being able to take 20mA is a maximum rating that is safe
for
the chip, but for this to happen the operating condition that Vss<Vin<Vdd
is
violated. hence you are causing yourself a whole lot of grief by not
observing
the operating conditions clauses. It is like saying that a 100V transistor
can
take 10A, but to have 1000W dissapation is violating its 150W rating!!!!!!!

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