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LMV771: Deviant behaviour in TINA-TI and PSICE-for-TI simulation

Christoph Katz
Prodigy 10 points
Part Number: LMV771
Other Parts Discussed in Thread: TINA-TI

Good day,

I'm currently trying to model a amplifier ciruit. I'm using TINA-TI (9.3.200.277 SF-TI) and PSPICE for TI (17.4-2023) and compared the results of the ac frequency sweep. Here is the relevant part of the circuit and the corresponding bode plots:

 

TINA circuit

  

TINA results (Plot is V_adc/Vin in dB)

   

PSPICE circuit

   

PSPICE results:

   

If I now change the resistor value of R22 in PSPICE from 9.96kOhm to 9.959999999kOhm I get the same result as in the TINA simulation. I am using the latest componenten models from https://www.ti.com/product/LMV771#design-tools-simulation. 

I was wondering if you could help me confirm if this is a bug or if I am missing something?


Thank you very much in advance for your answer!

 

With kind regards

Christoph katz

  • 0
    TI__Genius 13985 points

    Hi Christoph,

    We can look into the model but it appears the DC voltages show the amplifier to be running in open-loop, meaning that the amplifier cannot force the input voltages to be the same likely because the output is too close to the rail.  Since we can't see the rest of the circuit, we don't know what voltages it is biased at.

    There are slight differences between the PSPICE and TINA models, specifically on how they handle the output as it gets saturated (or, too close to the rail).  I suspect this is what you are seeing, but, we wouldn't recommend that you rely on any AC performance when the output is at 60 mV anyway.  The open-loop gain, or "Large Signal Voltage Gain" spec. is specified with the output at least 200 mV from the rail.

    Can you adjust the bias voltage so the output voltage is at least 200 mV and check again?  

    Regards,
    Mike