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OPA2189: OPA2189 direct replace ADI/OP2177 is fail

Alex Chen9
Expert 1075 points

Part Number: OPA2189

HI sir

I use the OPA2189 to replace to ADI/OP2177 in 6 gain amplifer,

i found the OPA2189 output Oscillation, IC bady hot,

Do you have any suggestion. adjust R/C?

  • 0 in reply to Alex Chen9
    Guru 140200 points
    Hi Alex,

    can you show a scope plot? What is connected to the output of OPA2189?

    Kai
  • 0 in reply to Alex Chen9
    TI__Guru* 93105 points

    Hi Alex,

    The OPA2189 shouldn't become unstable unless the circuit configuration adds enough phase shift around the feedback loop to result in positive feedback. If the phase margin is marginal in the circuit small differences between op amps may result in stability, or instability. Therefore, as Kai mentioned we need to see what is connected to the output of the OPA2189. Better yet, it would be helpful to see what is driving the OPA2189 and what power supply decoupling is being used at its power supply pins. More information is always better than not enough information.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Alex Chen9
    Expert 1075 points
    I design a 6 gain amp by negative feedback, I short the PIN3 to ground, to monitor the output, i found the out pin show the noise,please advise it.
    thanks
  • 0 in reply to Alex Chen9
    TI__Guru* 93105 points

    Hello Alex,

    We really need to have the circuit information that I requested in my earlier response. The gain of 6 V/V information and schematic segment alone are not enough for us to assess what could lead to the OPA2189 instability.

    • Previously you indicated that the issue is an output oscillation, but in the latest response you mention "noise." Can you provide a DSO image of what it is you are seeing at the OPA2189 output? Please make sure that the DSO volts/div and time/div are indicated.
    • Did you obtain the OPA2189 device(s) from TI, or one of an TI's authorized distributors?

    If we receive the information needed to do a thorough circuit assessment we should be able to determine what is causing the unexpected output.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    TI__Genius 11135 points
    Alex

    We haven't heard back from you so we assume you were able to resolve your issue. If you need additional help just post another reply below. Try to include additional circuit information as Thomas suggested above.

    Thanks
    Dennis