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TCAN1044A-Q1: CAN BUS being drop while VCC/VIO turned ON, is this behavior correct and why it behave like this ?

PYTsai
Genius 11495 points
Part Number: TCAN1044A-Q1

Hi 

My customer observed that (as shown in below waveform) CAN BUS being drop while VCC/VIO turned ON.

Why ?

CAN bus side has no any device connected, it is floating. 

is this behavior correct and why t behave like this ?

  • 0
    TI__Guru 74252 points

    PY,

    This is not typical behavior. Is it possible to share a schematic?

    Regards,

    Eric Hackett 

  • 0 in reply to Eric Hackett
    TI__Genius 11495 points

    Hi Eric,

    pls check schematics below, thanks ! 

  • 0 in reply to PYTsai
    TI__Guru 74252 points

    PY,

    On the load switches, why do they have the VIN and VOUT tied together? Or are the red boxes indicating that these resistors are not populated? I'm not sure if this is any reason why the CAN bus would do this, but I'm curious why the circuit is configured this way.

    The fact that the CAN bus voltage is not only dropping, but going to a negative level, is what is peculiar here. It may be an effect of the oscilloscope probe grounding, but does this happen at any other point during operation, or only when the device is powering up? And what happens if you power up VCC and VIO at different times?

    Regards,

    Eric Hackett