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TINA/Spice/OPA1641: Reporting Spice model error

Part Number: OPA1641
Other Parts Discussed in Thread: TINA-TI, , OPA1671

Tool/software: TINA-TI or Spice Models

Hi guys,

My customer found this and wanted to report it to be fixed (not time sensitive, as it is not impeding their progress):

"The OPA1641 Spice model on your web site has problems when the positive power supply (VCC) is too low. Depending on the configuration (inverting, noninverting) you need to apply anywhere from 3.5 to 4 volts on the VCC terminal to make it behave.

 

BTW, the PSpice model from your web site was dropped in to LTSpice.

Other OPA-type opamp models have worked fine in LTSpice."

Thanks,

Brian

  • Hi Brian,

    Thank you for reporting this issue. Can you please ask for a simulation file (LTSpice is fine) which shows the issue that I can use to debug?

    By the way, keep in mind that the maximum input common-mode voltage range of the OPA1641 is 3.5V below Vcc. If they are applying input signals centered around 0V, or AC-coupling, then they'll need that much headroom on the supply.

    Best regards,

    Ian Williams
    Applications Engineer/SPICE Model Developer
    Precision Amplifiers

  • Oops, the common mode input voltage answers why this didn't work in my case. I didn't read the spec sheet closely enough. The Spice model is probably correct as the Vcm range was my issue.
    The power supply specification in the data sheet is confusing since the data sheet says the minimum power supply voltage can be ±2.25V with Vcm = Vout = midsupply (zero volts in my case). I was intending to use ±2.5V for the power supply which clearly doesn't work.

    Thanks anyway!

    -Brian
  • Hi Brian,

    I'm happy that it was simply a spec issue. FET-input op amps like the OPA164x family often have this limitation near the positive supply rail. 

    However, if having rail-to-rail input is useful in your application, I recommend taking a look at the OPA1671. It's a brand new device optimized for low-voltage operation on a CMOS process. The input and output are fully rail-to-rail, and it's got low noise, low distortion, and 12+MHz of gain bandwidth while consuming just under 1mA of current.

    Best regards,

    Ian Williams