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OPA2694: Follower mode

Nicolas Bouquet
Intellectual 435 points
Part Number: OPA2694

Hello,

Can the OPA2694 be used in follower mode (meaning no Rg)? Any special things to know about this IC in unity-gain mode?

The datasheet only mentions "Note that a 430Ω feedback resistor, rather than a direct short, is recommended for the unity-gain follower application" and "UNITY GAIN STABLE BANDWIDTH: 1500MHz"

What BW can I expect with small signals, unity-gain mode with Rf=430ohm and no Rg?

Thank you

Nicolas

  • 0
    TI__Genius 15555 points

    Hello Nicolas,

    Current feedback amplifiers need to have a feedback resistor to operate properly, this includes the device when used as a voltage follower. There are recommended feedback resistor values shown in figure 11 for each gain configuration. When the datasheet mentions "Unity Gain Stable Bandwidth" this is measured with a 430Ω feedback resistor as well.

    Best,

    Hasan Babiker 

  • 0 in reply to Hasan Babiker31
    Guru 48195 points

    Well Nicolas, as the datasheet says, unity +1 gain Rf = 430ohm, SSBW approx. equal to 1.5GHz. 

    More of a marketing number, not really super reliable

    1. There is some feedthru included in this, 

    2.Assuming 100ohm load, 

    3. Gain of +1 will be slew limited in the input buffer, but not specified. 

    Most of the specs are gain of +2 or -1V/V with a 50ohm to 50ohm load, much more reliable data. 

  • 0 in reply to Michael Steffes
    TI__Genius 15555 points

    Hey Nicolas,

    In addition to Michael's comment, I would also suggest running simulations on TINA or Pspice.

    Best,

    Hasan Babiker