SN74AVC4T245: IBIS Model Accuracy Concerns with Respect to High/Low Drive Strength

Stephen Zinck

Part Number: SN74AVC4T245

Tool/software:

Hello Folks,

From the datasheet for the SN74AVC4T245, it would appear that the drive strength, high versus low, is symmetrical. The IBIS model, under a 1 meg-ohm test load, shows they are not the same. A x16 version of this device on the TI website shows an Hspice model. When this Hspice model is tested in a similar manner, it does not exhibit the same behavior as IBIS - it has similar drive high/low strengths and more in line with expectations.

Is the x16 Hspice model valid to use as a stand-in for the x4 device? Does the x16 Hspice model behavior reflect the actual device behavior? Does this call into question the accuracy of the IBIS model?

Regards,

Steve

6 months ago

0 Joshua Salinas 6 months ago

TI__Mastermind 22650 points

Hello Steve,

Our team is looking into this and will respond as soon as we can. Thank you!

Regards,

Josh

0 Stephen Zinck 6 months ago in reply to Joshua Salinas

Prodigy 10 points

Hello Joshua,

Do you have an update regarding this issue?

Thank you,

Steve

0 Stephen Zinck 6 months ago in reply to Stephen Zinck

Prodigy 10 points

Hello Joshua,

I figured it might make sense to provide a couple of waveforms to better demonstrate the issue. The first plot below is of the Hspice model (red trace) and IBIS model (blue trace) under a 1Meg-ohm test-load at typical PVT. The second plot has a source-series, 22-ohm resistor, a 12-inch, ideal, 50-ohm transmission-line with a 1Meg-ohm test-load at typical PVT for both model types (again Hspice=red trace, IBIS=blue trace).

Steve

Plot #1

Plot #2

+1 Joshua Salinas 6 months ago in reply to Stephen Zinck

TI__Mastermind 22650 points

Hello Stephen,

Thank you for your patience. After checking with the team on this, you are correct in stating the currents are not symmetrical. We can even look at the Pull-up and Pull-down tabs on the IBIS model and see non-symmetrical currents. For now I would recommend sticking with the 16-bit HSPICE model as we work to revision the IBIS model. HSPICE model can work since both AVC16T and AVC4T have similar architectures.

Regards,

Josh

0 Stephen Zinck 6 months ago in reply to Joshua Salinas

Prodigy 10 points

Hello Josh,

Thank you very much!

Kind regards,

Steve

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SN74AVC4T245: IBIS Model Accuracy Concerns with Respect to High/Low Drive Strength