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TCAN1043A-Q1: The CANH / CANL differential signal trace impedance control

Kai Lai
Expert 8966 points
Part Number: TCAN1043A-Q1

Hi Team,

As title mentioned, does we have a suggest that the differential signal trace impedance should design as single end 60 ohms of each trace or differential 120 ohms on the PCB board ?

I'm not asking the Terminal 120ohm, is the PCB board  trace impedance. Such like when we design a PCIE high speed differential trace we will control the trace impedance in PCB design.

Thanks!

Kai

  • 0
    TI__Guru 53555 points

    Hi Kai,

    The typical characteristic impedance for the cabling used in CAN applications is 120-ohms. In order to minimize the impedance changes presented to the signal, the trace impedance can be matched to this 120-ohm value. 

    Note that CAN busses operate at much lower frequencies than interfaces such as PCIE, and are therefore less sensitive to impedance changes on the scale of relatively short PCB traces (compared to the length of the entire cable harness). Therefore, it is common for board designs to use thicker trace widths for the CAN lines to increase the current capability and protect the traces from fault conditions rather than choose to match a 120-ohm impedance which can result in relatively narrow traces for only marginal benefit to the analog signal. 

    Let me know if you have any more questions.

    Regards,
    Eric Schott

  • 0 in reply to Eric Schott1
    TI__Expert 8966 points

    Hi Eric,

    Then how about the TXD and RXD, does we have any differential signal trace impedance suggestion / trace length limit ? 

    Thanks!
    Kai

  • +1 in reply to Kai Lai
    TI__Mastermind 26806 points

    Hi Kai,

    At the data rates used for CAN FD communication, usually these lengths are not necessarily a consideration. The RXD output of the TCAN1043A-Q1 is spec'd with a DC VOL based upon ±2 mA current sourcing/sinking - strong enough to provide good rise/fall times from the pin. That being said, as good design practice, I like to keep these under 15 pF.

    Of course, this is system-dependent, and any requirements of the TXD line would be based upon the microcontroller. That being said, there isn't necessarily a trace length limit for these digital pins.

    Best,

    Danny

  • 0 in reply to Danny Bacic
    TI__Expert 8966 points

    Hi Eric, Danny,

    Thanks for your comment!

    hope you have a wonderful holiday 

    BR,

    Kai