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Isolating an off-the-shelf CAN device with back to back CAN Transceivers

Nick Wernicke
Intellectual 775 points
Other Parts Discussed in Thread: ISO1050

I have an off-the-shelf CAN device that does not have galvanic isolation between its CAN port and its ground.  I would like to isolate this device.  Is that possible to do with two can transceivers (perhaps ISO1050DUB) connected back to back? Will the built in bus arbitration prevent this from working?

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    TI__Mastermind 20590 points

    You are correct, how CAN arbitration works prevents this from working.  I believe you are trying to describe the below diagram as a way to isolated this CAN device.  This will not work as you mention due to the way CAN arbitration works.  The CAN transceiver receiver always mirrors back what is on the network so the arbitration will work and thus if you connect 2 ISO1050 devices back to back with an implied cross wiring of the RXD/TXD digital signals on the two ISO1050 devices you will create a positive feedback loop between all the transceivers connected in this fashion once a dominant bit is transmitted in the system.  There is no simple way to make "after the fact" isolation on the CAN network due to how arbitration and CAN works.  In addition the below solution adds the additinal loop time of 2 CAN/Isolation stages to the total CAN loop time which will have to be accounted in cable lenght or data rates where necessary.   

    One option would be if the off-the-shelf CAN device could be modified to add isolation in it's signal path, if low quantities, maybe bypass the internal CAN XCVR and route TXD / RXD / Power GND to the CAN connector on the unit and then connect a simple ISO1050 based Isolated CAN unit at that point.