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RS-485 Isolation

Craig Carder1
Intellectual 510 points

Hello,

     I have an application where I have a large RS-485 bus that needs isolation on one section of the bus.  Meaning I need isolation on the differential (A, B, Y, Z) side.  I don't have control over the peripheral design so I can't add an isolated transceiver.  Are there any options for isolation A to A, B to B, etc.

     One though was to put two transceivers back to back with one of them isolated.  Could this work?  In this case it would be differential to singled ended (TX, RX) to single ended (RX, TX) through an isolation barrier back to differential (A, B, Y, Z).

     I'm not sure if this is possible since I wouldn't know how to handle RE# and DE other than pulling them always on.  I've look at some off the shelf isolators and this is how they do it.  

     If anyone has any insight, let me know if I'm on track or not.

Thanks

Craig

  • 0
    TI__Mastermind 20820 points

    Hi Craig,

    This topic comes up from time to time and you are on the right track with your thinking. Several years ago one of our great systems and applications engineers, Thomas Kugelstadt, wrote a great app note on the topic. The application report can be found here: 

    Here is a link to a reference design we did on the topic as well:

    Please let me know what questions you have and I will be glad to address them!