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Do we need to control impedance of CAN BUS ?

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  • Do we need to control impedance of CAN BUS ?

    Hi All,
    Hi Robert,


    My hardware design is most similar to imx Open Rex design development board and I have included CAN BUS port to my custom design.

    In my memory layout I controlled impedance as 100 Ohms for differential pair and 50 Ohms for single ended signals.

    Do we need to control impedance of the CAN BUS traces ? If yes what is the impedance value ? Can CAN BUS signal traces affect to memory layout if I didn't control CAN BUS trace impedance ?

    Regards,
    Kulunu.

  • #2
    I think, CAN may have different types of terminations. This may help you:
    http://www.ni.com/white-paper/9759/en/

    From the link:
    " High-Speed/FD CAN Termination

    For high-speed/FD CAN, both ends of the pair of signal wires (CAN_H and CAN_L) must be terminated. This is because communication flows both ways on the CAN bus. CAN_L is pin 2 and CAN_H is pin 7 on the standard 9-pin D-SUB connector. The termination resistors on a cable should match the nominal impedance of the cable. ISO 11898 requires a cable with a nominal impedance of 120 Ω; therefore, you should use 120 Ω resistors for termination. If you place multiple devices along the cable, only the devices on the ends of the cable need termination resistors. Figure 1 shows an example of how to terminate a high-speed network.
    "
    "Do we need to control impedance of the CAN BUS traces ? If yes what is the impedance value ?"
    - You may want to. See the note above (we used 100OHM for the short tracks in OpenRex)

    "Can CAN BUS signal traces affect to memory layout if I didn't control CAN BUS trace impedance ?"
    - no

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