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TCAN1043A-Q1: fault pin questions

jiansong zhu
Prodigy 10 points
Part Number: TCAN1043A-Q1

During interface test, when CANL  short to GND, fault pin will jump between 0 and 1 frequently. But other test items, CANH short to Vcc, short to GND, fault pin will keep in 0 until short  disappeared.

  • 0
    TI__Mastermind 26806 points

    Jiansong,

    Please excuse the delay during the holiday season. One of our experts should be able to get back to you with more information next week after the holiday.

    Happy New Year!

    -Danny

  • 0
    TI__Guru 53555 points

    Hi Jiansong,

    The fault detection circuit used in TCAN1043A measures the relative current on the CANH and CANL pins when the driver is in a dominant state. If the current through these pins is not to an expected value or there is too large of a difference between the currents through CANH and CANL, the device will recognize a fault and report low on the nFAULT pin after four consecutive dominant-to-recessive transitions where the fault is detected. If on fault is detected on the CAN bus for four consecutive dominant-to-recessive transitions, then the fault flag is cleared and nFAULT will clear back to a high state.

    In the case of a weak short on the CAN bus where the current measured on the CAN pins is close to the threshold set internal to the device, it is possible that the circuit can give different results based on the length of the dominant-time on the bus. This means that given the varying dominant-times present when CAN data is being driven on the bus, the circuit may assert and clear the nFAULT status periodically throughout transmission. 

    Typically weak faults such as this will have minimal impact on the CAN signal and data will still be able to be transmitted on the bus without issue. In this case where no CAN errors are being reported by the CAN controller, the state of the nFAULT pin can be ignored. If the system begins to recognize CAN errors, then it may check the state of the nFAULT pin (which should remain constant low in the case of a strong fault that causes errors) to determine if the errors are the result of a hardware fault. 

    Let me know if this is clear and if you have any more questions. 

    Regards, 
    Eric Schott