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rail to rail op amp transition

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by drkidd22, Jul 19, 2017.

  1. drkidd22

    drkidd22 Member

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    Hello,

    I'm working on a circuit that needs a buffer. I was going to use the OPA344 as is rail to rail.
    The input voltage range at pin 3 is from 0.18V to 3.1V and the output goes to an analog input of a microchip.
    Within that wide range there are other smaller ranges that the software uses to make decisions, for example from 0.18 to .28 blue .38 to .58 red .78 to .98 green etc.

    One thing I noticed is that the OPA344 datasheet mentions there is a transition region where a small discontinuity may occur. From the datasheet it looks like problems can occur between 1.5 to 2.5V input voltages as the opamp switches rails. So I don't think this will be a good part for this application. I need something that's stable through the entire range of 0.180V to 3.1V.

    Any ideas?
    unityopa344.PNG
     
  2. kubeek

    kubeek Well-Known Member

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    Note the opamp has rail to rail output range, but not input. Input needs to stay lower than Vcc-1.5V, so less than 1.8V in your case. Where in the datasheet do they talk about this discontinuity?
     
  3. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The OPA344 opamp has an input voltage range that is a little more than rail-to-rail. It is done with two differential pairs at the inputs, an N-channel one and a P-channel one. Page 9 of the datasheet describes the discontinuity as it switches between the differential pairs.
     
  4. dave

    Dave New Member

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  5. drkidd22

    drkidd22 Member

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    So how can I prevent errors in this continuity range? Just stay out of it?
     
  6. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    The amp could be used in inverting mode. If you can stand inversion. Then the inputs will be at 1/2 supply all the time.
     
  7. OBW0549

    OBW0549 Member

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    That discontinuity is likely so small you would have extreme difficulty even measuring it, much less is it likely to be large enough to have any detectable effect whatsoever on your circuit's operation. You're wasting your time worrying about it.
     

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