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TINA/Spice/LM4041-N: Problems with LM4041 model when not ground referenced on the - (anode)

Tim Burke81
Prodigy 75 points
Part Number: LM4041-N
Other Parts Discussed in Thread: TINA-TI

Tool/software: TINA-TI or Spice Models

I keep running into extremely slow simulations using one of the LM4041 models from the TI site (LM4041_NC1P2).  I have had success in addressing these issues with replacing the LM4041 with an ideal 1.225 voltage source.  While this works, there are clearly many parameters that are not going to modeled correctly with such a strategy. 

Note that I have a test bench that seems to simulate just fine for transient, DC, AC.  A .noise simulation does not return meaningful results (I assume the part is not truly noiseless ).  One thing I have noticed is that if you use an ideal DC voltage source and a bias resistor, and the negative (anode) side is connected to ground, everything simulates fine.  Swap the resistor and the LM4041, and that is when everything falls apart.  Many practical circuits are not ground referenced, severly limiting the usefulness of the LM4041 model.

There are a lot of models for the LM4041 up on the TI web site.  I am using the -NC1P2 model. I was thinking of perhaps trying some other models.  I don’t remember why I chose the LM4041-NC1P2 model originally.

I found this thread and I suspect the issue is the same, and won't be resolved.

https://e2e.ti.com/support/development_tools/webench_design_center/f/234/t/571997?tisearch=e2e-sitesearch&keymatch=LM4041

I have a few question:

  1. What is the difference between all the models on the web site?
  2. These models also state they are transient models.  Am I to assume that the other simulations are only valid for Transient simulations?
  3. I was thinking about using the dynamic impedance and device capacitance to better model the reference when under the proper bias.  I imagine the capacitance is probably non-linear though, which makes modeling it more difficult.
  4. Is there additional noise beyond the thermal noise of the dynamic impedance that the LM4041 generates?
  5. Are there any plans to update this model with a more accurate model, like the GWL initiative TI has for Amplifiers?

Thanks!