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TCAN1043-Q1: The wave of CANL is abnormal.

Part Number: TCAN1043-Q1

Hi all

     The wave of CANL is abnormal, like this picture, the green wave is CANL, when CANL is up,there is a groove.

      How can I make the wave be up always? 

  • Went,

    This looks like a node coming off the main bus, is there any way you can tell me how long the conductors connecting CANH and CANL are? The "hump" in the rising edge from CANL could be caused by some kind of reflections on the line. Also, can you tell if the CANH and CANL traces are symmetrical?

    Regards,
  • The  CANH and CANL are very closed.The trace is  symmetrical. The CANL and CANH are about 20mm long.

    Is there about R and C,effected the wave ?

    What is value of  33pf C?

  • Went,

    Thanks for the information, this stub length wouldn't cause any issues. This small dip looks like a reflection, or something is affecting the CANL driver for a very short amount of time. Since this waveforms are identical up to this point, asymmetries don't make sense.

    33pF helps with emissions by slowing down edges and absorbing high frequency noise that will propagate along the CAN bus. The resistance and capacitance that are shown wouldn't cause this issue in a typical application.

    Does this bump in the CANL waveform happen every single dominant to recessive transition? Or is this specific to an event in the application?

    Regards,