ADA4000 stability issue

I tried replacing a TL082 which was working fine in the attached circuit with ADA4000.

I am very unhappy with the stability fo ADA4000. The input is from an DAC (100KHz) and the output is at output pin of Opamp.

What could be a direct replacement for the ADA4000 (SOT23-5 Package)?

Sibi

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  • The ADA4000 seems to be a fine replacement for the TL071. If you have problems with it, there is probably an issue with your design and not the ADA4000. I see three things that could be improved in your design:

    1.) Place a small compensation capacitor in parallel to R18. 22pF or 47pF is probably a good starting value.

    2.) The power supply capacitors C18 & C22 are pretty large (4.7uF ceramic). They can have a low resonance frequency. Replace them with e.g. 470nF or place a 100nF in parallel.

    3.) The low-pass capacitor C24 could be increased to e.g. 470pF to reduce the steps coming from the DAC.

    Without a picture of the layout, these are all the recommendations I can make.

    Best Regards,

    Dirk

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  • The ADA4000 seems to be a fine replacement for the TL071. If you have problems with it, there is probably an issue with your design and not the ADA4000. I see three things that could be improved in your design:

    1.) Place a small compensation capacitor in parallel to R18. 22pF or 47pF is probably a good starting value.

    2.) The power supply capacitors C18 & C22 are pretty large (4.7uF ceramic). They can have a low resonance frequency. Replace them with e.g. 470nF or place a 100nF in parallel.

    3.) The low-pass capacitor C24 could be increased to e.g. 470pF to reduce the steps coming from the DAC.

    Without a picture of the layout, these are all the recommendations I can make.

    Best Regards,

    Dirk

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