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TCAN1043-Q1: CAN BUS Failures, Detection & Flag Clearance

Martin Stein
Intellectual 1335 points
Part Number: TCAN1043-Q1
Other Parts Discussed in Thread: TCAN1043

Hello,

I have two topics regarding CAN bus failure detection.

1) Is TCAN1043 able to detect a short between CANH and CANL ? Measurements and datasheet seem to show that nFault-pin does not signal the short state. How is such a failure handled / detected by the system ?

2) In event of nFault going low because of CANL/H short to GND / VSUP, how is it cleared after removal of short ? It is not cleared automatically. What is the procedure the host MCU must perform ?

The EVM User Guide states:
Flag is cleared: If fault is not present for four consecutive dominant to recessive transitions or upon leaving normal mode
Datasheets states:
Flag is cleared: Upon leaving Normal mode

Thank you

Martin

  • 0
    TI__Guru 71512 points

    Martin,

    Thanks for bringing this to our attention, may I ask what kind of application this is?

    1) Technically no it will not detect a short between CANH and CANL. The CAN bus fault detection mechanism compares the differential current of the bus to a reference threshold. In the case where CANH and CANL are shorted together, it will merely look like a constantly recessive level to the receiver comparator, so no issue will be detected by the detection circuit. The best way to detect this indirectly is to monitor the bus for an extended time where the controller is only receiving recessive bits. Since the CANH and CANL are shorted, there will never be a voltage differential to trigger the dominant threshold in the receiver, so there will be a constant stream of recessive level plus bit stuffing bits going to the controller.

    2) The flag is cleared if the bus fault condition is absent for four consecutive dominant to recessive or transitions while still in Normal mode, or if the device is transitioned out of normal mode the nFAULT pin will not indicate the bus fault anymore. If the device is transitioned back to Normal mode and the CAN bus fault condition is still present, the nFAULT pin will indicate the failure after four dominant to recessive transitions on the TXD pin.

    Please let me know if you have nay other questions.

    Regards,