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Original question:

TINA/Spice/OPA855: PSPICE MODEL FOR OPA855

OPA855: OPA855 Faulty Sim with Spice Model

Sojhal Brochal
Prodigy 50 points

Part Number: OPA855

Tool/software:

I am simulating the OPA855 to be used as a TIA.  I am using LTSpice as that is the software I'm most familiar with.  Attached below is the schematic, the circuit on the right is where I try to use the OPA855

You will notice two lib directives.  Firstly I try to use the OPA855 spice model as is, in the same directory as the simulation file.

Unfortunately it complains about a pin mismatch.

....net(11): Number of nodes does not match number of pins (6) of sub-circuit "opa855".
X§U2 Ref N001 VCC VEE Vout_OPA855_A level1 OPA855 Avol=6.3k GBW=8000Meg Vos=0 En=0 Enk=0 In=0 Ink=0 Rin=500Meg

I worked around it by creating a copy of the OPA855 spice model and adding a dummy pin as such

And then specifying the sim file to use that file instead.

The simulation will now run however the results are bogus, for example the transfer function is as shown

The circuit should have 63.5 dB gain with a 3 dB cutoff at 100 MHz

Any help in correcting the simulation would be greatly appreciated.


Thanks,

Sojhal

  • 0
    TI__Mastermind 31845 points

    Hello Sojhal,

      Would you be able to test the OPA855 in LTSpice in the standard configuration to eliminate any convergence issues using LTSpice? 

       If it matches above response, we can move to the circuit level. 

    Thank you,
    Sima

  • 0 in reply to Sima Jalaleddine
    Prodigy 50 points

    Hi Sima,

    Simulating the circuit the same way in the reference design also still yields inaccurate results.

    My circuit schematic is shown below:

    it yields the following AC response

    I have attached my simulation files incase that helps.

    Thanks,

    SojhalLTSpice OPA855 TIA.zip

  • +1 in reply to Sojhal Brochal
    TI__Mastermind 31845 points

    Hello Sojhal,

      Thank you for testing this on your end and sharing your files. I was able to get the standard configuration on my end

       I am not familiar with LTSpice, therefore symbol is not ideal. But, I attached files below. The method I inserted the model: from Kai in this e2e thread

    1. I opened in LTSpice the "OPA855.LIB" file and selected the line which contains the .subckt in the lib file to right click and automatically generate a model.

    2. Then I imported the generated model like a normal component into my schematic (via the "AND gate" in the header), which I picked up from the folder [AutoGenerated].

    0410.OPA855.zip

    Best Regards,

    Sima