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TCAN1051H: CANHL=CANL=2.5V, when TXD=0V

Wesley Huang
Expert 1030 points
Part Number: TCAN1051H
Other Parts Discussed in Thread: TCAN1051, TCAN1051-Q1

Hi team，

 

I met some problem when I used TCAN1051, could you please offer some advices for my issue?

  1. When the TXD=1 or no connection, the CANH=CANL=2.5V and it is normal.
  2. But When the TXD=0, the CANH CANL is still 2.5V which is wrong.

 

        3. At first, I though that it was caused by the protection after the CANH and CANL, so I let the R50 and R49 to be NC, but the situation is not changed.

The schematic of TCAN1051 and protection circuit is shown below (by the way the R46,R47,R10,R11 is always NC).

 

Best Regards

Wesley Huang

  • 0
    TI__Guru 59762 points

    Wesley,

    Thanks for sharing the schematic and oscilloscope screenshots. Can you verify the state of pin 8? And are you sending a switching signal into TXD or just changing the state to a constant 1 or 0?

    Regards,

  • 0 in reply to Eric Hackett
    Expert 1030 points

    Eric

    1. I click the "this has resloved my issue" wrongly. Please help me recall it.

    2. Pin8 is always 0.02V. The TXD is not switching and always 0.

    Regards,

    Wesley

  • 0 in reply to Wesley Huang
    TI__Guru 59762 points

    Wesley,

    No worries about the misclick, we can continue the thread.

    The TCAN1051-Q1 has a feature called dominant timeout. This feature disables the CAN bus driver if there is a dominant detected on TXD for longer than tTXD_DTO. So if TXD is held at 0, there will be a a dominant signal for ~2ms, but then the bus will go back to recessive. To see the correct transitions, an alternating square wave at 250kHz on the TXD pin will transition the CAN bus dominant and recessive at a sufficient rate to not trigger the dominant timeout.

    Please let me know if you have any other questions.

    Regards,