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TCAN1042HG: CAN Bus terminal resistor issue

Red Yen
Expert 4320 points
Part Number: TCAN1042HG

Hi Support team 

my customer have a major issue regarding CAN Bus communication issue.

  1. We have maximum 6 rectifiers in parallel.
  2. If each rectifier with 1 terminal resistor 120R inside, CAN Bus will become unstable-----totally terminal resistor becomes 120/6=20R.
  3. If no terminal resistor in each rectifier, then CAN Bus no communication.
  4. Can we add a CAN repeater on each rectifier to solve this problem??
  5. How this CAN repeater work?? And How to add this repeater to my rectifier CAN Bus??
  6. Can you show us its schematics and functions??
  7. Can you give us some Demo board for test once if this solution works.

  • 0
    TI__Guru 62920 points

    Hi Red,

    CAN repeater circuits may be an option, but these carb be complex to design and will introduce some timing variation that could be problematic if several are cascaded in series. I'd recommend trying a few simpler solutions first. The best would be to configure the system so that termination is included at only two nodes - is this possible?

    If not, another option would be to increase the termination value to 360 Ohms. This solves the issue of too much loading, but adds a couple of other risks you'll need to assess. One is that the termination impedance will not perfectly match the cable impedance (assuming a cable impedance of 120 Ohms). This would likely only be a problem for longer cable connections, though, and may not be a concern here. The other potential issue to keep in mind would be the maximum data rate achievable when fewer than 6 nodes are connected. For example, with just two nodes the effective load resistance would be 180 Ohms. Under this condition the CAN state transitions will be a little slower, so the maximum possible data rate will decrease. If the application operates at a lower data rate, though, then this may not be a concern either.

    Regards,

    Max

  • 0 in reply to Miguel Robertson
    TI__Genius 9710 points

    Dear Max,

    If we try to use CAN repeater in parallel, that mean, each rectifier CAN interface with one CAN repeater, then connected to CAN Bus.

    Then, does it solve my problem??

    BR

    Kevin

  • 0 in reply to Kuan Wei Chen (Kevin Chen)
    TI__Guru 62920 points

    Hi Kevin,

    I may be misinterpreting what you have in mind, but if a CAN repeater were placed at every node it seems like you would have the same problem.  Just instead of overloading the CAN transceivers on the rectifiers, you would overload the CAN transceivers on the repeaters (assuming you still had termination at each node).  Repeaters could work if they divided the bus into different segments, each with two 120-Ohm terminations.  I still think this solution would be too complicated, though, and so you would be better off trying to modify the termination scheme first.

    Regards,
    Max