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TCAN1042HGV: falling edge of CANH and rising edge of CANL

Jerry Chen
Expert 5110 points
Part Number: TCAN1042HGV

Hi,

I'm replacing MC33901 with TCAN1042HGVDR. Customer found both the falling edge of CANH and rising edge of CANL are not monotonic as below shows. It happened on all the units in this board. How to explain this? And, what is required rising and falling time of CANH\L? I attached the schematics.

Thanks.

  • 0
    TI__Guru 62920 points

    Hi Jerry,

    This sort of ringing is common in multi-node networks and can occur as reflections from unterminated nodes bounce back and interfere with the transmitted signal.  (The recessive level is only weakly biased on the CAN bus rather than actively driven, so it is more susceptible to these kinds of events.)  This should not result in any bit errors, since the RXD value reported by each transceiver will be correct at the time that the controller at each node samples it.

    To confirm this is the true root cause, you could try to disconnect the transmitting node from the network, add termination resistance as necessary to achieve an equivalent 60-Ohm load between CANH and CANL, and re-measure the waveforms.  If the ringing goes away, then you would know it is arising from the network rather than the transceiver.

    Max