Is there a way to disable the ESD protection diodes on the PSoC3 pins?

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MiSt_296941
Level 4
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25 replies posted 10 replies posted 10 questions asked

This may sound like a dumb idea, but when you are trying to multiplex Thermocouples into the DelSig and you want any kind of channel to channel isolation, those diodes get in the way!  Anyone have any suggestions?  We are really close to releasing this product so a board design change is not possible.

Mike.

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1 Solution
Anonymous
Not applicable

The diodes are there rightfully so, and they should never be disabled. Your problem is in the common mode noise not in the Psoc! and for that there are a few techniques like analog isolation, instrument amplifiers....

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5 Replies

Unfortunately that App note does not address channel to channel isolation at all.

Mike.

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Vasanth
Moderator
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250 sign-ins 500 solutions authored First question asked

Hello Mike,

Unfortunately it will not be possible. The ESD didoes cannot be disabled. How  much one channel input is influencing the other channel ?

Best Regards,
VSRS

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Well, I was pretty sure that was what the answer would be for the negative side (diodes that are internally grounded), but the positive side goes to Vddio.  If we didn't need to drive any pins high, then if Vddio was left unconnected those diodes would be effectively not there (although commoned together they are back to back from channel to channel).

This is not a case of one channel influencing the other UNLESS there is a voltage difference between them (common mode) that then causes the diodes to conduct.  This can happen from 60Hz AC being coupled to long lines in an industrial plant.

Mike.

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Anonymous
Not applicable

The diodes are there rightfully so, and they should never be disabled. Your problem is in the common mode noise not in the Psoc! and for that there are a few techniques like analog isolation, instrument amplifiers....

0 Likes