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SN65HVD230: Stub Length in SLLA270.

Kengo.Y
Guru 11285 points
Part Number: SN65HVD230


Tool/software:

Hi team,

I'm considering to using the TCAN1044.
I found the application note(SLLA270) for Stub Length.
Can bellow comment in application note still be used?

>To minimized reflections, stub-line length should not exceed one-third (1/3) of the line's critical length.

BR,
Kengo.

  • +1
    Guru 318050 points

    Yes.

    But it's a rule of thumb. Every stub creates signal distortions, and the distortions increase with stub length. That limit makes the bus work in most applications, but you should always make the stub as short as possible, and, conversely, a longer stub might work in certain applications.

  • +1 in reply to Clemens Ladisch
    TI__Guru 74322 points

    Kengo,

    Clemens is correct, this is a rule of thumb based on the timing of the signal and the reflections caused by the stub. It is just a rule of thumb, but works, and in general, you should make the stubs in your system as short as possible.

    If you cannot avoid stubs, you can also add termination resistance to these nodes of a higher resistance to absorb some of the signal so the reflection will be mitigated. The resistance added at these nodes needs to not lower the overall CAN bus resistance to less than 57 ohms though, so keep that in mind when calculating the overall parallel resistance if extra termination is added.

    Regards,

    Eric Hackett