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ESD on ADM2687 board

Question asked by AlgaeEater on Nov 20, 2013
Latest reply on Nov 20, 2013 by RAnslow

Hi All -

 

We are spinning a board which uses your very fine ADM2687 and are planning to add some degree of ESD protection.

Not trying to meet any particular standard at this time.

 

An MCC SM712 and 10 ohm series resistors as per AN-960 seems like a good idea.

I assume the SM712 should clamp to GND2, but am not sure how to handle the 485 shield.

Currently it just floats though one node grounds it (a RS485 dongle on the server).

 

We would like the possibility of having one of our nodes assume master status if the server fails or is absent, so it seems that a weak connection (1 -> 10K ?) between GND2 and shield may be desirable.

 

There is currently a 220V varistor between GND1 and GND2 though I am not sure what purpose it serves.

Should this be removed ?

 

Could you explain why terminating with a resistor and large, high quality, series cap is undesirable as mentioned in AN-960 ?

 

Also could you recommend a twisted pair cable with shield suitable for runs up to 1500 ft ?

 

 

Many thanks for any suggestions -

 

AE

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