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OPA891: As Power Amplifier

John La Grou
Intellectual 330 points
Part Number: OPA891

The OPA891 data sheet front-page "Applications" section cites "Professional Audio Amplifier" but the minimum recommended build-out resistance is 20R.

I assume the "Pro Amplifier" refers to a headphone amplifier (150R) rather than something to drive, say, a 4-ohm speaker?

Has anyone at T/I tried using this part in parallel to increase output current? Any OPA891 audio apps would be great, especially if this can be used to drive conventional 4R speakers, etc..

  • 0
    TI__Genius 10200 points

    Hi John,

    I was wondering if you could show me where you found the minimum load requirement of 20R. The device could very well drive a lower load like the 4R you are referring to however we can expect the output swing to be limited because of the heavy load. In terms of the parallel setup, we have not tested this specific device in that kind of configuration but there shouldn't be a problem doing so.

    Best Regards,

    Ignacio

  • 0 in reply to Ignacio Vazquez Lam1
    Intellectual 330 points

    In audio power, such as driving headphones, there can be modest to significant capacitive load. On page 19 of the OPA891 data sheet it says "...for capacitive loads greater than 10 pF, place an isolation resistor in series with the output of the amplifier. For most applications, a minimum resistance of 20 Ω is recommended."

  • 0 in reply to John La Grou
    TI__Genius 10200 points

    Hi John,

    Thank you for clarifying, that is correct. During the validation/design process, the device performed better with those Riso recommendations when driving a capacitive load. We always advice to stick with the values suggested in the datasheet.

    Best Regards,

    Ignacio