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TCAN1043-Q1: some questions

Jiawei Hu1
Expert 5625 points
Part Number: TCAN1043-Q1
Other Parts Discussed in Thread: TCAN1043

Hi team,

We did the CAN BUS failures diagnostic test and found:
HHT's two-way CAN This test is in line with expectations, but Lotus only has CANH shorted to Vsup, we found that CAN can still communicate normally, and no abnormal error is reported.
We made a verification that when the CAN of Lotus is configured in FD mode, when its CANH is short-circuited to Vsup, an error can be reported normally.
Question:
Why does the CAN Bus Failures diagnosis meet expectations when your company's TCAN1043DRQ1 is configured as CAN FD, but when it is configured as normal CAN, the CANH-to-Vsup short circuit cannot report an error?

Attached is the schematic. See page14.

BR

Jiawei

  • 0
    TI__Guru 53575 points

    Hi Jiawei,

    The fault detection circuit in TCAN1043 requires that the CAN driver remains in a dominant state for at least tCBF (1.9us) before a sample will be taken of the CAN bus fault state. If the dominant time is less than this amount, no measurement is taken. If the dominant is greater than this amount, a measurement is taken of the CAN bus fault state. The device requires four consecutive measurements to return a fault state before it will be indicated on the nFAULT pin. In normal CAN or CAN FD communication, this requirement is met during arbitration for rates 500kbps or slower (2us bit time or longer). During the FD portion of a CAN frame or when using other protocols at faster data rates, the bit-time may be shorter than 1.9us so fault measurements do not occur as regularly. 

    Also important to note is the impact of a common mode choke or any inductive elements on the fault detection circuitry. Because these elements promote symmetrical AC properties, they increase the amount of time needed for the circuit to reach a steady state during a fault condition. This effectively makes the sample time of 1.9us not yet stable where the fault detection circuitry cannot detect the presence of any existing fault. Therefore, it may be necessary to increase the dominant time (reduce data rate or drive a pattern of consecutive zeros) in order get an accurate fault reading of the CAN bus. 

    What data rates are being used during the two tests described here? Please include both nominal (arbitration) and data (FD) rates. 

    Regards,
    Eric Schott