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OPA3S328: OPA3S328 spice model not working in LTSPICE

Antoine Hamel
Prodigy 20 points
Part Number: OPA3S328
Other Parts Discussed in Thread: TINA-TI, PSPICE-FOR-TI

Hello,

I'm trying to simulate the OPA3S328 using the provided spice model in LT Spice XVII.

I wired the circuit exactly like the figure 1-1 in the sboa521 application note. When I run a simple .op simulation for DC operating point I get the following error in the SPICE log:


WARNING: Less than two connections to node U1:_OPA3S328_SWITCH:_U24:_U1:NVCC. This node is used by E:U1:_OPA3S328_SWITCH:_U24:_U1:V.
WARNING: Less than two connections to node U1:_OPA3S328_SWITCH:_U22:_U1:NVCC. This node is used by E:U1:_OPA3S328_SWITCH:_U22:_U1:V.
WARNING: Less than two connections to node U1:_OPA3S328_SWITCH:_U25:_U1:NVCC. This node is used by E:U1:_OPA3S328_SWITCH:_U25:_U1:V.
WARNING: Less than two connections to node U1:_OPA3S328_SWITCH:_U23:_U1:NVCC. This node is used by E:U1:_OPA3S328_SWITCH:_U23:_U1:V.
WARNING: Less than two connections to node U1:_OPA3S328_SWITCH:_U26:_U1:NVCC. This node is used by E:U1:_OPA3S328_SWITCH:_U26:_U1:V.
WARNING: Less than two connections to node U1:_OPA3S328_SWITCH:_U27:_U1:NVCC. This node is used by E:U1:_OPA3S328_SWITCH:_U27:_U1:V.


This seems to be internal to the model and the problem seems to happen only when the included analog switch are part of the feed back loop. If I don't include the switch in the amplifier feedback loop everything works even the switch themselves.

Can anyone validate if the model is correct?

Thanks

  • 0
    TI__Mastermind 21240 points

    Hello, 

    We do not support LT Spice, however we offer for free Tina Ti and also Pspice for Ti both of which have functioning models that can be found on the product home page. 

    Tina Ti can be downloaded here:

    https://www.ti.com/tool/TINA-TI

    Pspice for Ti can be downloaded here

    https://www.ti.com/tool/PSPICE-FOR-TI

    Best Regards, 

    Chris Featherstone

  • 0 in reply to Chris Featherstone
    TI__Guru 52396 points

    Hi Antoine,

     Regarding the application note release date, the app note precedes the model release above.  The app note simulations use the exact same op-amp amplifier core model, but use a simplified switch impedance model, but provide an accurate estimate of stability, noise, stability and bandwidth.  See TINA-TI examples below:

    TINA Closed-Loop Transient and AC frequency response File (Example):

    OPA3S328_2Mohm_closed_loop_example_keep.TSC

    TINA Open-Loop AC Stability Analysis File (Example):

    OPA3S328_2Mohm_open_loop_stability_example_k.TSC

     Thank you and Regards,

    Luis 

  • 0 in reply to Luis Chioye
    Prodigy 20 points

    Thanks for the application note simulation files.

    My plan is to simulate a whole analog front end using the OPA3S328. Since I'm not very familiar with TINA-TI or Pspice for TI, are there any limitation I will encounter if I decide to switch to one of those before I commit to learning a new simulation environment? I'm thinking of  Node limits size maybe? Or model compatibility? Maybe that is a question for a different thread

    Thanks for the quick reply, very much appreciated.
     

  • 0 in reply to Antoine Hamel
    TI__Guru 52396 points

    Hi Antoine,

    The OPA3S328 official release TINA-TI or PSPICE-for-TI models, shown on Chris post above consists of two parts,  the op-amp OPAx3228 block and the switch model. The OPAx328 op-amp block has no issues. and works flawlessly on both simulators.  However, the switch model block is known to exhibit some convergence issues primarily on TINA-TI, and in seldom cases, convergence issues on PSPICE on certain circuits or configurations, such as the AC open-loop stability analysis.  The models are already on the queue for revision to address the issue.

    The TINA-TI files provided on my post above, from the application note, use exactly the same OPAx328 op-amp block with the complete op-amp specification, including AOL, output impedance over frequency, noise, offset and input/output range limits, etc..  However, the application note preceded the OPA3S328 model release and therefore used a simplified switch model. This simplified switch is based on the typical parasitic resistance and capacitance on the switch (RON, CIN and COUT).  This provides a good first order approximation to check stability, bandwidth and noise on the TIA circuit.  

    It would be your preference, if you would like to learn PSPICE-for-TI or TINA-TI.  We support both simulators.  If you require assistance simulating your circuit, please let us know. 

    Thank you and Regards,

    Luis