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TCAN1469-Q1: CANHBAT is continuously detected during CANTRCV busfault detection function

Do-hyun Kim
Intellectual 305 points
Part Number: TCAN1469-Q1

Tool/software:

I am experiencing a phenomenon where CANHBAT is continuously detected during the CANTRCV busfault detection function. Could this be due to the terminating resistor?

We are currently checking, but please check if the symptom can occur when the sum of the terminal resistances connected in parallel is low.

  • 0
    TI__Guru 74252 points

    Do-hyun,

    Yes, the way that bus fault detection works is through differential current and voltage measurement, which is directly affected by the termination resistance on the CAN bus. It is pertinent that the fault detection feature be used only when 60 ohms of termination is present on the bus. If the parallel resistance is low, then the amount of current being read by the transceiver would be high, and that could point to a CANH short to VBAT condition.

    What is the termination resistance on the CAN bus?

    Regards,

    Eric Hackett 

  • 0 in reply to Eric Hackett
    Intellectual 305 points

    I don't know the exact value of the termination resistor, but the parallel value of the termination resistor is definitely lower than 40 ohms.

  • 0 in reply to Do-hyun Kim
    TI__Guru 53555 points

    Hi Do-hyun,

    The CAN standard defines an expected differential load between CANH and CANL to 60-ohms. These are the conditions that the bus fault detection circuit was calibrated for, so it is not too surprising to hear that the transceiver is reporting a fault under the <40-ohm load condition. 

    What is the purpose of such a large differential load for this system? Is there is reason the typical two 120-ohm termination resistors is not used here? 

    Regards,
    Eric Schott