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Isolated RS485 Ground Connection

Question asked by teap on Mar 24, 2015
Latest reply on Mar 24, 2015 by RAnslow

Talking about isolated RS485 line side interface connections.

Many typical ADMxxxx application circuit figures are showing a four pole connector on the line side interface (RX+, RX-, TX+, TX-)

without any (isolated) ground for the line side interface (e.g. see fig. 45 in the ADM2687E data sheet).

I'm wondering what is recommeded for isolated to isolated differential I/O lines (e.g. ADMxxxx line side connected to the line side of another ADMxxxx), regarding the (isolated) ground connection.

When both ADM ports of the differential link are isolated and there is no (isolated) ground connection between them,

how to maintain the recommended common mode voltage range of the receiver when there is no common reference?