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TCAN1042-Q1: TX dominant timeout

Ivy Jin
Expert 3075 points
Part Number: TCAN1042-Q1
Other Parts Discussed in Thread: TCAN1044A-Q1,

Hi team,

My customer uses TCAN1042DRQ1 in their project. And they met below question, could you please help give some comments? Thank you!

For the TX dominant timeout feature of the TCAN1042DRQ1, as described in the datasheet, the Transmitter feature is turned off when the TCAN1042 triggers the DTO, until TX Pin clears Dominant.

Below is the customer measured waveform, CH1&CH2 are CAN Bus, CH4 is TX Pin;
After TX Pin short to GND, The TCAN1042 triggers the Dominant timeout and releases the CAN Bus in time, but when the dominant error does not clear, CAN bus is also affected by TX dominant error.
This phenomenon is not in line with the datasheet, please help figure out the possible cause, thank you.

Regards,

Ivy

  • 0
    TI__Mastermind 25526 points

    Ivy,

    You're right that those appear to be DTO lengths (I'm eyeballing about 2 ms for each of those dominant periods you highlighted), and are much longer than the expected lengths of standard error frames (I'm assuming your arbitration data rate is something around 250 kHz - 1000 kHz?). Could you confirm your arbitration bit length just to be sure?

    It looks like these events are happening during attempted communication. Could you help clarify how you're looking at TXD? i.e., are there any passives or long traces between your probe and the IC's input pin? Also, it would be helpful to zoom in on the TXD pin horizontally to see whether there are any glitches that might be bringing TXD briefly high?

    Your understanding is correct that TXD dominant time-out will keep the driver off until TXD returns to a high state.

    As a side-note, please consider TCAN1044A-Q1 for new projects, as this is the newer version of 8-pin CAN. The TCAN1042-Q1 is still active, but it is the older technology and currently does not have the same capacity increase over time that's planned for TCAN1044A-Q1.

    Best,

    Danny