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TCAN1043HG-Q1: Know more about conditions when nFAULT signal is triggered.

Khyati Sapariya
Prodigy 20 points
Part Number: TCAN1043HG-Q1
Other Parts Discussed in Thread: TCAN1043

Hi,

I have two question related to fault condition -

I have a processor interfaced with transceiver (TCAN1043HGDQ1) and also I have connected microchip CAN analyser on the same bus.

1. Refer section 10.3.6 CAN Bus Failure Fault Flag in datasheet, it says 'These failures are detected while transmitting a dominant signal on the CAN bus' when any of the six condition is true:
1. CANH bus pin shorted VSUP
2. CANH bus pin shorted VCC
3. CANH bus pin shorted GND
4. CANL bus pin shorted VSUP
5. CANL bus pin shorted VCC
6. CANL bus pin shorted GND

Does this means that fault will occur only when processor is transmitting data on TXD pin of TCAN1043HGDQ1 and any of the six condition is true? or also it will detect fault when CAN analyser (any other node on the same bus) is transmitting data on CAN bus ?

I tested both conditions, nFAULT is triggered (LOW) only when data is transmitted on TXD pin of TCAN1043HGDQ1 and nFAULT is HIGH when data is transmitted by any other node on the same bus.

2. Can I have the expected nFAULT signal so that I can compare it with what I can see?
I have attached all four signal which I can see on the scope.
In the attachment, Green is the transmit data and Yellow is the nFAULT signal.

When CAN_LO is shorted to GND and when CAN_HI shorted to VCC, nFAULT is low for just few cycles. In this case other nodes connected on the same bus receive data even after nFAULT is LOW. I do not understand why other nodes should receive data when fault condition has occurred. Can you please justify?

CAN_LO shorted to GND:

CAN_HI shorted to VCC:



When CAN_LO is shorted to VCC and when CAN_HI shorted to GND. nFAULT goes low immediately when data is transmitted unit fault condition is cleared. This seems to be correct.

CAN_LO shorted to VCC:

CAN_HI shorted to GND:



Hope to hear from you soon.

Thank you,
Khyati

  • 0
    TI__Mastermind 49975 points

    Hi Khyati,

    Khyati Sapariya said:
    Does this means that fault will occur only when processor is transmitting data on TXD pin of TCAN1043HGDQ1 and any of the six condition is true?

    Yes, TCAN1043 will only detect these fault conditions when it is transmitting data. Fault detection is not active on received dominant bits. 

    Khyati Sapariya said:
    I do not understand why other nodes should receive data when fault condition has occurred. Can you please justify?

    Not all fault conditions prevent data from being transmitted on the bus. In the case of CANL short to GND or CANH short to Vcc/Vbat, the differential signal can still propagate through the second unfaulted CAN line. For example, when CANL is shorted to GND and CANH pulls dominant, the resulting Vdiff can still exceed the 900mV requirement for the receivers to recognize the dominant. In contrast if CANH was shorted to GND, CANL can only drive a GND potential on the unfaulted line and no meaningful differential can be created. 

    The difference in driver characteristics is also less apparent during one of these non-disruptive faults. The device will detect the fault by sensing the difference in current through CANH vs CANL. This is more subtle in a non-disruptive fault than when CANH is shorted to GND for example. This is likely why you're seeing a difference in behavior of the FAULT pin during these test cases. 

    Let me know if this makes sense and if you have any more questions.

    Regards,
    Eric Schott

  • 0 in reply to Eric Schott1
    Prodigy 20 points

    Hi Eric,

    It completely make sense. Thank you so much.

    Best Regards,

    Khyati