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TCAN1042V-Q1: About CANH/CANL

Junya Kato
Expert 1635 points
Part Number: TCAN1042V-Q1

Hello Team,


Can CANH / CANL communicate under the following conditions?

1) Input-mode,     CANH:Normal,                         CANL:GND-short
2) Input-mode,     CANH:Normal,                         CANL:Battery-Voltage-short 
3) Input-mode,     CANH:GND-short,                   CANL:Nomal
4) Input-mode,     CANH:Battery-Voltage-short, CANL:Nomal
5) Output-mode,  CANH:Normal,                         CANL:GND-short
6) Output-mode,  CANH:Normal,                         CANL:Battery-Voltage-short
7) Output-mode,  CANH:GND-short,                   CANL:Nomal
8) Output-mode,  CANH:Battery-Voltage-short, CANL:Nomal


Best regards,
Kato

  • 0
    TI__Guru 62910 points
    Hello Kato-san,

    Communication will not work if CANH is shorted to GND or if CANL is shorted to battery (cases 2, 3, 6, and 7 above). In these cases, the CAN output driver would be unable to create a sufficient differential voltage between CANH and CANL.

    Communication may work (albeit more marginally, with abnormal signal waveforms) if CANH is shorted to battery or if CANL is shorted to ground (cases 1, 4, 5, and 8). In these cases, the shorted line remains static (at whatever voltage is it shorted to) while the other line will still toggle. This generally produces a large enough differential signal to be correctly interpreted by a CAN receiver. One caveat to this is that larger-than-normal currents will need to be sourced by the CAN driver during the dominant state. (For example, when CANH is shorted to the battery, the 60-Ohm termination of the CAN bus will present a strong load to the CANL pull-down driver.) In this situation, it is possible that the power dissipation in the transceiver is high enough to trigger thermal shutdown.

    For more detailed information on how short-circuits can impact CAN communication, you may want to reference this post: e2e.ti.com/.../590053.

    Best regards,
    Max
  • 0 in reply to Max Robertson
    Expert 1635 points
    Hello Max-san,

    Thank you so much for your prompt response.

    Best regards,
    Kato
  • 0 in reply to Max Robertson
    Expert 1635 points

    Hello Max-san,

    It is an additional question.
    Is it possible to communicate if CANH/CANL is under the following conditions? How will it behave?

      9) Input-mode,    CANH:Normal,  CANL:Open
    10) Input-mode,    CANH:Open,     CANL:Nomal
    11) Output-mode, CANH:Normal,  CANL:Open
    12) Output-mode, CANH:Open,     CANL:Nomal

    Best regards,
    Kato

  • 0 in reply to Junya Kato
    TI__Intellectual 2885 points

    Hello Kato-san,

    For CAN to differentiate an input or output signal the voltage differential (CANH – CANL) must be VD ≤ 0.5V or VD ≥ 0.9V. The voltage differential does not care about positive or negative voltages only the difference between them. Each scenario you listed will work, but It might be more likely to send incorrect bits as the thresholds for proper bits has been greatly reduced