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OPA2227: OPA2227 Stability

Ken Worthington
Prodigy 20 points
Part Number: OPA2227

I am seeing what appear to be stability issues with OPA2227 amplifiers.

The circuit is a simple inverting circuit (non-inverting input ground), gain -1, with +/-15V supplies. Input and feedback resistor 10K, and 33pf between output and inverting input.

There is 100mVp-p at 100MHz on the output, which is only visible with an active probe. If you add a little capacitance to the output (e.g. a passive probe the noise goes). Just to confirm this is causing offset errors in circuits connected downstream, which go if you connect a passive probe to the inverting circuit output.

Also, not all OPA2227 amplifiers show this problem, usually replacing the device fixes it. 

Has anyone else had this problem?

  • 0
    TI__Expert 5830 points
    Hello Ken,

    we have seen this before and have found a solution by placing a 20ohm + 500pF snubber at the output of the OPA2227 output to ground. This will create a pole-zero pair that reduces the bandwidth and accounting for stability resulting in the elimination of the offset error.

    Best regards,

    Errol Leon
    Texas Instruments
    Precision Amplifier Applications Engineer
  • 0 in reply to Errol Leon6
    Prodigy 20 points
    Hi Errol,

    I have tried your suggestion, and it fixes our problem.
    However, I have a lot of OPA2227s in the design and adding four extra components to each would be a bit of a problem. So, I will try to find another device for the future.

    Thanks,
    Ken