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TINA/Spice/INA828: Spice/ INA828

Part Number: INA828
Other Parts Discussed in Thread: TINA-TI,

Tool/software: TINA-TI or Spice Models

I created the following test circuit:

INA828 is supplied with single +5V. The reference voltage is set to 1,5V. The gain is set to 50 (Rg = 1K). The common mode voltage is set to 2,5V. Both inputs are connectet to each other. I used the spice subcircuit to simulate the behavior. The expected output value is 1,5V. The simulation result is 1,5186V.

I need your help.

Best regards

Ronald Foth

  • Hi Ronald,

    I was able to duplicate your issue. The reason for the higher-than-expected offset in the SPICE model is because in your test configuration, the output stage amplifier is going into input saturation. The valid input common-mode voltage (Vcm) range for the INA828 is +2V above and -2V below the supply rails, so for a single-supply scheme of +5V and 0V that means the valid Vcm range is from +2V to +3V. With Vref = 1.5V, the input voltages to the output stage amplifier are trying to go just below 2V, which in turn activates that amplifier's input Vcm clamp.

    Please note that Vcm vs. Vout behavior for INAs with our current SPICE model architecture is still a work in progress. For now we recommend using our INA SPICE models for small-signal transient and AC, noise, and basic functional analysis with split power supplies and Vref = Vcm = Vs/2. To verify the input/output behavior of the INA as a function of Vcm, Vref, gain, and Vs, please use our INA-CMV-CALC (INA Common-mode Voltage Calculator) tool. With your settings, the calculator shows that you can apply a differential input of +54mV to -28mV and achieve linear operation.

    Best regards,

    Ian Williams
    Applications Engineer/SPICE Model Developer
    Precision Amplifiers

  • Hi Ian,

    thank's for your answer. I already used the INA-CMV-CALC before. And when I see at the green line, I don't expect any problem with my set of parameters. I interpret your answer in the way that the spice model has still a problem but the INA-CMV-CALC shows the real behavior of the hardware?

    Best regards
    Ronald Foth
  • Hi Ronald,

    That is correct. Our SPICE model currently has a problem handling the input/output voltage limitations of the INA828, but the INA-CMV-CALC results will match real silicon.

    Best regards,

    Ian Williams

  • Ronald

    We haven't heard back from you so we assume this answered your question. If you need additional help just post another reply below.

    Thanks
    Dennis