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TCAN1042-Q1: no common GND between CAN notes

Martin Steube-Henkel
Intellectual 1740 points
Part Number: TCAN1042-Q1
Other Parts Discussed in Thread: ISO1042-Q1, ISO1042

Hello 

our customer is developing a 12V BMS (right block) with a LS switch for disconnecting the battery pack from the car power supply T31.

In case the switch is open the CAN transceivers of BMS and ECU (or diagnosis tool) on the left don't have a common GND and are floating.

Will this cause some issues? And how to overcome? One idea is to use a ISO1042-Q1 connected on both sides of the switch.

I found this thread a about 

https://e2e.ti.com/support/interface-group/interface/f/interface-forum/128310/is-can-communication-working-between-two-different-ground-suppling-cardsn  

They made a test without common GND and this seems to work. I am not aware about the common mode they have in this case. 

Thanks 

Martin

  • 0
    TI__Guru 53535 points

    Hi Martin,

    The TCAN1042 is designed to support a wide common mode range of +-30V to accommodate for large ground shifts between nodes. This will allow the transceiver to continue to operate correctly even with a very different ground reference from the transmitting transceiver. The high bus fault protection rating of +-70V (H version) will also minimize the risk of damage when first connecting the two nodes when the potential difference may be even larger. If the common mode voltage between CAN nodes is expected to be greater than 30V during normal operation, it may be necessary to implement a solution that uses galvanic isolation like the ISO1042. 

    Do you know approximately what ground potential difference you're expecting in this application? 

    Regards, 
    Eric Schott