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OPA211: Operational Amplifier Vout issue at 0V input voltage applied.

prabhu k
Prodigy 165 points
Part Number: OPA211
Other Parts Discussed in Thread: OPA205, OPA192

Hi TI Team,

In my design, we are using Precision Operational Amplifier OPA211AIDR. At 0V input voltage Vout is - 0.24V and current is -21.34 mA. Kindly review below circuit and suggest any correction required ?

  • 0
    TI__Mastermind 21137 points

    Prabhu,

    1. I suspect instability may be the problem.  Can you look at the circuit with an oscilloscope and see if the -0.24V is an oscillation?  I did run a stability test on the model and do not see a problem in simulation, but this kind of abnormal output is often an oscillation that looks like a DC signal on a DMM.  What is the output connected to?  Is there any capacitive load?
    2. Where do you measure the -21.3mA?  Are you sure that this is only due to the OPA211.  This high current could also be due to an instability.
    3. Unrelated to your issues:  the OPA211 may not be the best choice for your application.  I am not sure what your selection criteria were, but the OPA211 is commonly used because of it's good noise.  It also has good input offset voltage.  However, it does not have the best bias current and current noise.  The Sallen-Key filter has a 30kΩ source impedance.  This source impedance generates it's own noise and also translates the OPA211 current noise into voltage noise.  Thus when you use OPA211 with a 30kΩ source resistance you don't really benefit from the low noise.  Also, the bias current translates into a significant offset, so you don't benefit from the low offset of the OPA211 either.  There may be some other parameter in the OPA211 that you selected it for.  If you were targeting low noise and low offset, you might look at the OPA192 or OPA205 as alternatives.
    4. In trouble shooting the OPA211 circuit, can you connect the input directly to GND so that you know nothing from a previous stage is the issue.  Also, disconnect the output from the next stage (or load).  In other words, disconnect the input and output so that the OPA211 circuit is not impacted by other circuits.
    5. If this is a single prototype, you might double check the soldering to make sure there isn't a solder bridge to ground or a supply.  You should also confirm the component values match the schematic.  Also, confirm the power supplies are stable and accurate.
    6. Did you get the device from an authorized TI vendor (e.g. digikey)?  There have been some cases of counterfeit devices from unauthorized vendors.
    7. Damage to the device could also cause this kind of behavior.
    8. See attached power point and TINA simulation files for support.

    I hope this  helps and you are able to resolve the issue soon.

    Best regards,  Art

    Sallen-key simulations.pdf

    opa211 stability sallen-key.TSC

    noise and offset for OPA211 SKF.TSC