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TCAN1043-Q1: short test of TCAN1043-Q1

Yao Zeng
Prodigy 100 points
Part Number: TCAN1043-Q1
Other Parts Discussed in Thread: TCAN1043

Hi,TI partner：

   When I short the  CANH(pin13) to 12V or GND, the nFAULT(pin8) is Low.But when I short the CANH(pin13) to VCC(pin3) ,the nFAULT(pin8) presents periodic changes, you can see the two pictures for details. What's the reason?

  • 0
    TI__Mastermind 19050 points

    Hi Yao,

    I'm looking into this and will get back to you by tomorrow.

    Regards,

    Sean

  • 0
    TI__Mastermind 19050 points

    Hi Yao,

    The bus fault detection circuit for TCAN1043 works by measuring and comparing the currents through the CANH and CANL pins while the transceiver is driving the bus dominant. The circuit evaluates the current reading when the driver moves from the dominant to recessive state. If a bus fault condition is recorded for four consecutive dominant to recessive transitions, the nFAULT will indicate a CAN bus failure flag by driving the nFAULT pin low. Because of the parasitic and transmission line characteristics of the CAN bus, it takes some time for the current through the CAN driver to stabilize after starting to drive a dominant. This current settling time is dependent on the system and may change based on characteristics such as bus load, cable length, node count, etc. 

    In this case if you are testing on an active CAN bus it is possible that the dominant time is no long enough for the bus to settle to the point where an accurate current reading can be measured within one dominant bit time. For this reason the device is only able to accurately measure bus faults when the data rate is 500kbps or less. 

    When a bus fault occurs that is relatively weak such that it does not significantly impact the data on the CAN bus, it is possible that the current measurement of the fault detection circuit does not recognize the condition to be outside of the fault detection thresholds. For this reason, we recommend that the fault detection data only be referenced if the system recognizes an increase in bus errors. This would indicate a possible hardware fault that is impacting the data reliability of the CAN bus that could be further diagnosed with the fault detection feature of the transceiver. This could take the form of sending a slower CAN frame or one padded with additional consecutive 0s (to increase the dominant time) so a more accurate fault detection result and be captured by the transceiver.

    Regards,

    Sean