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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:
    This document presents an overview of the various physical layers for controller area networks. It details which NI CAN products support which layers and how to correctly terminate each layer.


    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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