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ISO1044: ISO1044

DRUILHE yvan
Intellectual 540 points
Part Number: ISO1044
Other Parts Discussed in Thread: ISO1050

Hello,

The goal is to isolate a CAN bus using the ISO1044 component.

Does the attached diagram work and is there no bus blocking?

The CAN card is a commercial card, the aim is to have an isolated CAN bus.

Thank you for your help.

Best regards

iso_can.pdf

  • 0
    TI__Mastermind 29595 points

    Hello,

    This configuration should work and provide isolation from the CAN card ("Carte CAN") to the HE308. 

    I noticed that the highlighted GNDs use the same symbols. I am assuming the GND"0" (inside the red boxes) is a separate GND net. If this is correct then I can confirm that the +5V, VCCISO1 and VCCISO2 rails are all independent and on their own isolated Grounds. 

    Let me know if you have further questions. 

    Best,
    Andrew 

  • 0 in reply to Andrew J
    Intellectual 540 points

    Hello

    We won't have this type of problem following this note that we found on your site?

    https://e2e.ti.com/support/interface-group/interface/f/interface-forum/507422/can-differential-signal-isolation-using-two-sn65hvd234d

    ***********************************************************************************************

    With this circuit, any single dominant bit would cause the bus to be stuck dominant. (For example, if the bus connected to U26 is dominant, its RXD would go low, then the TXD input of U28 would go low, then the U28 CAN output would be dominant, making its RXD output also low, which then makes the U26 output dominant, etc.)

    Would it be possible to simply use isolated CAN transceivers (like ISO1050) instead? That tends to be the usual approach to this problem.

    Thank you for your help.

    Best regards

  • 0 in reply to DRUILHE yvan
    TI__Mastermind 29595 points

    Hi, 

    Sorry for the confusion. You are correct this configuration would cause a bus lock-out condition and therefore not recommended. The typical configuration would be to have an ISO1044 on the CAN Card directly connected to the bus and another CAN transceiver (or another ISO1044) on the opposite node, CAN Filtre. 

    A CAN isolator on just one of these nodes (CAN ISOLE or CAN FILTRE) would achieve isolation and also allow for a simpler design since the opto-isolation section could be removed altogether. One transformer driver could be used which would simplify the design further.

    The original E2E post is correct. It would be simpler to use an isolated CAN transceiver to control the bus. 

    I have also found another post where the wording is a little clearer if it helps Sharing TX and RX of two CAN transceivers - Interface forum - Interface - TI E2E support forums.

    Best,
    Andrew  

  • 0
    Intellectual 540 points

    Hi,

    Does the issue of isolated CAN have a straightforward solution? Or is using software to manage this function using a micro behind isolated tranceiver truly necessary?

    Best regards

  • 0 in reply to DRUILHE yvan
    TI__Mastermind 29595 points

    Hi,

    I am not sure I understand the question. A CAN transceiver, either isolated or non-isolated, will take logic inputs from the TXD and RXD lines and transmit/receive the information on the CAN bus. The typical connection for CAN is a controller connected to the TXD and RXD lines of a CAN transceiver.

    Isolated CAN would use an isolated CAN transceiver instead, to provide isolation between the controller and the CAN bus. 

    -Andrew