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OPA3S328: Difference between INx- and COMPx inputs

Dominic Leone
Prodigy 10 points
Part Number: OPA3S328
Other Parts Discussed in Thread: OPA3S2859

The 2 OPA have an INx- inpout and a COMPx input. they appear internally connected, so why have 2 separate inputs?

  • 0
    TI__Guru 52246 points

    HI Dominic,

    The OPA3S328 RGR (20-pin VQFN) package is below, where the two amplifies offer the standard -INx, +INx and OUTx pins.  The INSx and OUTSxx are the switch inputs and outputs.

    Kindly clarify, which diagram or document shows COMPx pins for the OPA3S328?

    Thank you and Regards,

    Luis

  • 0 in reply to Luis Chioye
    Prodigy 10 points

    I am sorry. i am working with 2 similar but different TIA OPA chips. I meant the OPA3S2859. very similar ICs. should i delete this and repost with proper part number

  • 0 in reply to Dominic Leone
    TI__Guru 52246 points

    HI Dominic,

    I am the Applications Engineer supporting the OPA3S328 .

    Let me refer your question to the High-Speed Amplifiers Applications team which will be able to support you with the OPA3S2859.

    Thank you and Regards,

    Luis

  • +1 in reply to Luis Chioye
    TI__Genius 14491 points

    Hello Luis,

    Thank you for referring Dominic over to HSAMPs!

    Hello Dominic,

    Good question: one of key features of the OPA3S2859 is the integrated switched feedback paths, which allow for 'gain switching' and having a small footprint with three different gain options.  A fourth an optional parallel non-switched feedback path is provided for applications where the switches would not be necessary or preferred.  This fourth optional path is the pinout from the inverting terminal directly to the INA- pin.  The other pins, such as COM_A & FBXs, are part of the integrated switch gain network.  

    You may refer to the first page of the datasheet for a diagram and quick summary of function; Sections 8 & 9 mention the fourth feedback path as well.  However, there is not an explicit diagram labelling the INA- pin as part of the feedback options; please know the 'fourth feedback path' would be using INA-.  These remarks are valid for the 'B' parameters of the other amplifier in the package, for which INB- provides a direct connection (no switch) to the internal amplifier.

    I hope this helps Dominic!  If you have any follow-up questions or questions about other parts or op-amps, please continue to use the forum Slight smile.

    Best,

    Alec