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OPA2111 common mode input range

Barry Volain
Prodigy 100 points
Other Parts Discussed in Thread: OPA211

Simulating an OPA2111 in TINA as a voltage follower with +/-5 volt supplies.  According to data sheet  CM input range is (V-)+1.8 to (V+)-1.4, so it should work for inputs between -3.2 to +3.6.  With a simulated +2.8V input, TINA shows output of 1.7V (should be 2.8V).  What's going on?  Bad model, bad TINA or bad me?

  • 0
    TI__Expert 3555 points

    Barry,

    Thank you for taking a look at the OPA2111 dual op amp. I have worked with the OPA2111 and found that the input common mode range is approximately equal to (V-)+4V to (V+)-4V (typical specifications). For your +/- 5 V supplies the range input common mode range would be from -1 V to +1 V.

    In your simulation, the fact that the output is limited to only 1.7 V makes sense. I would suspect that the model is providing you with a range the accommodates an CMRR ratio of ~ 75 dB, where the CMRR in the operating range ((V-) + 5V to (V+) -5V) is 100 dB (typ). The CMRR test conditions are (V-)+5V to (V+)-5V with supplies of +/- 15V.  

    This product was actually targeted for power supplies of +/- 15 V. I found it very frustrating to use this product with power supplies of +/- 5V. As an alternative amplifier I would suggest LM6081.

  • 0 in reply to Bonnie Baker - WEBENCH Design Center
    Prodigy 100 points

    Ok, now I see what happened. I THOUGHT I was using an OPA211 not OPA2111. The OPA211 data sheet title is "OPA2x11", so I stuck in the wrong device; there is no OPA211 device in TINA, only OPA2111, which I assumed is what I had in mind.
    I downloaded the OPA211 model, and now it works as expected.  (Actually, the model is OPAY211)

  • 0 in reply to Barry Volain
    TI__Expert 3555 points
    Barry,

    Fantastic. Hope the rest of your evaluation runs smoothly.