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OPA2189: OPA2189 for gain switch

Eddie Chou
Expert 6740 points

Part Number: OPA2189
Other Parts Discussed in Thread: TINA-TI, TS3A5017

Hi team,

My customer want to design PGA before ADC, they require low Vos (<6.8uV) and low noise (< 0.1mV ) in AFE design. we suggest OPA2189 with external mux for gain select.

Attached is schematic proposed from customer, would team help review and give some comments?

Or we have better solution to propose. 

Thanks & Regards

Eddie Chou

OPA2189 AGC.pdf

  • 0
    Guru 140200 points
    Hi Eddie,

    the multiplexer adds some parasitic capacitance to the -input of OPA2189. This introduces a phase lag in the feedback path and can erode the phase margin. So, I would add a suited phase lead capacitance from the -input of OPA2189 to its output.

    Run a phase stability analysis in TINA-TI to see which phase lead capacitance gives best results.

    Kai
  • 0
    TI__Guru 55466 points

    Hello Eddie,

    I have a few questions:

    - What is the expected amplitude range of the signal at the input of the OPA2189 circuit?  are these bipolar signals (swing above/below ground)? What is the frequency range of the signal?

    The reason I ask is because the OPA2189 is powered with bipolar +/-5V supplies, supporting input signals with a common-mode range -5.1V to +2.5V while the TS3A5017 multiplexer is powered with a unipolar 3.3V supply, supporting only unipolar 0V-3.3V signals.  A multiplexer with bipolar supplies will be required. 

    - Is the OPA2189 with PGA driving an ADC directly?  What ADC are they driving (and what is the sampling rate)?

    Thanks and Regards,

    Luis

  • 0 in reply to Luis Chioye
    TI__Genius 11135 points
    Eddie

    We have not heard back from you so we will close this thread. Please reply if further discussion is needed

    Thanks
    Dennis