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SN74AVC8T245: ibs model (AVC8T245_IO_33) show non-monotonic falling edges

Sheri Zhuang1
Prodigy 70 points
Part Number: SN74AVC8T245

We used the AVC8T245_IO_33 model for SigXP simulation. The waveform shows non-monotonic falling edges which do not match the measurement. This is very obvious with the typical case. The slow and fast cases seem to be okay.

However, simulation with simple connection with no transmission line shows some shelf in the falling edge of fast, slow and typical cases. Removing the package effect, the falling edge became smoother. Add the package back in, the typical case shows up as a complete reversal. Fast and slow cases are not as noticeable.

See attached pdf for details.

Thank you.

Sheri

non-monotonic falling edge_AVC8T245_IO_33_ibs model.pdf

  • 0
    TI__Genius 16725 points

    Hi Sheri,

    I am not sure how the IBIS models were created but they do assume worst case package parasitic when creating the model. This might be the reason behind the edges being smoother in your measurements when compared to the model.

    The difference between the fast case includes a strong process, assumption of -40C and a strong supply voltage. When in reality, your measurements will be a mix of strong, and typical case.The simulation should only be used to give you an idea of the actual measurements might look like. The real measurements are expected to be different than simulations.

    Thanks!

    -Karan