• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 34 subscribers
  • Views 340 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

TCAN1042-Q1: Fall into bus-off state when CAN H/L is open

TCAN1042-Q1: Fault code shows when power off its VCC

Hedy Hung1
Intellectual 325 points

Part Number: TCAN1042-Q1

Hi Team,

If system close TCAN1042VDRBRQ1 VCC, but its IO still has 3.3V, will that cause fault on diagnostic?

We insert each 5V on CAN H/L, and use the 5V and sinking current to calculate CAN H/ L impedance. When TCAN1042 has VCC, CAN H/L impedance is near 50Kohm, without VCC the impedance is near 25Kohm. 

From my understanding, the CAN H/ L impedance should unlimited as open loop when CAN transceiver is powered off. Am I right?

 

Thanks.

Hedy

  • 0
    TI__Guru 74302 points

    Hedy,

    Yes, that is correct if both supplies are gone from the transceiver. If VCC and VIO are at 0V, then the bus impedance will be ~2.5Mohms. However, with VCC at 0V and VIO present, the bus is still active and monitored for wake-up signals, and thus the impedance drops to Rin as described in the datasheet. This is also true if VCC is present and VIO is 0V. 

    When either of these conditions (one supply on, one supply off) is present, the device will take on a protected status of the mode it was previously in and the bus bias will depend on that. For normal mode, VCC/2, for standby mode GND.

    Please let me know if you have any other questions.

    Regards,

  • 0 in reply to Eric Hackett
    Intellectual 325 points

    Hi Eric,

    Can you describe "protected status of the mode"? what result can I see? such as fault code shown?

    Thanks!

    Hedy

  • 0 in reply to Hedy Hung1
    TI__Guru 74302 points

    Hedy,

    Protected status is enabled during an undervoltage condition on either VCC or VIO. When this occurs, the fully-functioning bus transmitter and receiver are disabled. As a result, the controller would "see" a CAN bit error every time it transmitted a dominant bit. This is because the RXD pin would be biased high through the protected state, and thus would never report a received dominant bit to the controller.

    Does this make sense?

    Regards,