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Advice on Selection of Amplifier

Jawwad Hafeez
Intellectual 870 points
Other Parts Discussed in Thread: OPA196, OPA197, OPA191, OPA192, OPA4192, OPA4187, OPA2189, OPA4197

Hi,

I am designing a Precision DC Voltage Drop Circuit with 4 Inputs.

12 to 4V

24 to 8V

36 to 12V

48 to 16V

For Voltage drop, I have chosen a precision resistor Network on input side and want to use an OpAmp Buffer to buffer the voltages. I need low input offset current, low input offset voltage, Low Offset Temp Co-eff. Low drift  and wider supply range, e.g. greater than 16 Vs, single supply Op Amp. I am considering OPA 197 for the purpose. 

Before I finalize the CAD, I request you to give your input and recommend this or other opamps ore instrumentation amps to chose from. I want to consider a few and prepare a comparison statement before moving on

Much appreciated

  • 0
    Guru 140200 points

    Hi Jawwad,

    what precision do you need? Can you give some numbers?

    Kai

  • 0 in reply to kai klaas69
    Intellectual 870 points

    Thanks Kai,

    I am looking for 

    Rail to Rail output,

    input to ground level, 

    better than 1 μV/°C maximum input offset drift
    better than 1 nA maximum input bias current

    better than 10-15 nV/√Hz maximum input voltage noise at 1 kHz

    less than 100 uV input offset 

    Input Temp Co-effic less than 100uV/degC

    Output Offset less than 200 uV

    Output Temp Co-eff less than 200uV/degC

    Input Bias Current less than 10nA

    Input offset current less than 5nA

    The application is DC so other than AC Stability at Unity gain  AC spec are not critical

    Regards

  • 0 in reply to Jawwad Hafeez
    TI__Guru 69431 points

    OPA197 and OPA196 should meet your requirements. If you need higher precision, you may also consider OPA192 and OPA191.  Output voltage offset is a function of input offset, close-loop gain and resistor mismatch used to gain up the signal and thus it is not controlled alone by datasheet specifications.

  • 0 in reply to Marek Lis
    Intellectual 870 points

    Thank you very much,

    Yes I do understand and calculate the output offset voltage based on  Input Offset V, Output Offset, Input Bias Currents and Gain and  resistors in feedback etc. 

    I am considering using OPA4192 and OPA4287. 

    The operation is single ended with V-=Gnd and V+ = 20V, the input includes Gnd. Gnd =< Gnd <= 18 V. The data sheet supports this. 

    Hope it will work perfect. 

    Regards

  • 0 in reply to Jawwad Hafeez
    Intellectual 870 points

    The Comparison of the two shows 

    Rail to Rail  - OPA 4187 - In to V- and Out

    Rail to Rail - OPA 4197 -  In and Out

    The Table 6.1 Absolute Maximum Ratings specify input = V- -0.5 to V+ + 0.5

    Plz advise

    Regards

      OPA4187 OPA4197
       
    Order now Order now
    Online datasheet Online datasheet
    Datasheet Datasheet
    Design & development Design & development
       
    Number of channels (# ) 4 4
    Total supply voltage (Min ) (+5V=5, +/-5V=10 ) 4.5 4.5
    Total supply voltage (Max ) (+5V=5, +/-5V=10 ) 36 36
    GBW (Typ ) (MHz ) 0.55 10
    Slew rate (Typ ) (V/us ) 0.2 20
    Rail-to-rail In to V- In
    Out Out
    Vos (offset voltage @ 25 C) (Max ) (mV ) 0.01 0.1
    Features Zero Drift EMI Hardened
    High Cload Drive
    Iq per channel (Typ ) (mA ) 0.1 1
    Rating Catalog Catalog
    Operating temperature range (C ) -40 to 125 -40 to 125
    Package Group SOIC | 14 SOIC | 14
    TSSOP | 14 TSSOP | 14
    Approx. price (US$ ) 2.00 | 1ku 1.35 | 1ku
  • 0 in reply to Jawwad Hafeez
    TI__Guru 69431 points

    Jawwad,

    There is a fundamental difference between OPA4197 and OPA4187 with former being a package-level trimmed (no active calibration) while latter being a zero-drift (self-calibrating), which has a significant effect on IB.  Also, OPA4187 is a much low power, lower bandwidth and thus higher noise that will NOT meet your 10-15nV/rt-Hz stated requirement. All in all, if you are willing to consider a zero-drift op amp in your application, you should take a look at OPA2189, which unlike OPA4187 will meet your noise specification.

  • 0
    TI__Genius 10850 points

    Hello Jawwad,

    We haven't heard from you in a while. We hope the issue was resolved. I am going to close this thread now. Please reply to re-open if you have any additional questions.

    -Tamara

  • 0 in reply to Marek Lis
    Intellectual 870 points

    Thanks Marek,

    I have gone through the data sheets and compared the two final opamps. 

    This has resolved the problem. 

    Regards

  • 0 in reply to Tamara M Alani
    Intellectual 870 points

    Thanks Tamara,

    Sorry for the delayed reply, I was busy in finalizing the pcbs that will use opamps as the input stage.

    Your help resolved the issues and cleared my understanding of the products.

    Thank you very much

    BR