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PCF8574 defective ?

Question asked by René Brunier on Aug 2, 2017
Latest reply on Oct 25, 2017 by TomE

Hello,

 

I'm using PCF8574 since more than 10 years to sense dry contacts (PCF is used in input mode). The contacts are located between 1 and 4 meters away form the board, and its action just consist to pull the input (P0-P7) to Vss. The environment is not a a lab but it is not too much "noisy".

This has been working very well so far until last months where I start to got strange behaviors:

As long a s the contact is very close to the PCF8574 (and cable length is short < 0.2m), its still working as designed.

If the cable length increase, at some stage (not always the same distance) the PCF8574 suddenly "collapse" Vcc, like if there is a shortcut inside (and the chips gets very hot).

Trying to understand, I did several experiments and conclude that the problem concerns a specific lot number:

 

               TH1780.102

               KnG14283

 

I do not know if and where I can retrieve data from this batch...

Can someone help

 

Thank's

Rene

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