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TCAN4550-Q1: CAN BUS last bit amplitude rise

Zion Twig
Prodigy 30 points
Part Number: TCAN4550-Q1

Tool/software:

Hi,

I have CAN bus with two TCAN4550-Q1 and two TCAN1044.

While communication we see last bit with higher amplitude than all other bits as shown below.

Any idea what may cause it? 

  • +1
    TI__Mastermind 33030 points

    Hi Zion,

    Yes this is correct behavior according to the CAN protocol.

    In the CAN protocol, this last bit is referred to as the ACK or Acknowledge bit and it comes from all receiving nodes on the CAN bus driving a Dominant bit at the end of a CAN message that was received without errors.

    The amplitude is larger because there are multiple nodes all driving dominant at the same time which results in more current flowing across the bus impedance and termination resistors.  Therefore a larger current flowing across the same resistance results in a larger voltage (Ohm's Law V = I x R).

    Regards,

    Jonathan