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Can the PGA281 be used in single-ended configuration with VOCM tied to VSON if only IN-P is used to optimize the output range?

SteveKK
Prodigy 150 points
Other Parts Discussed in Thread: PGA281, PGA206

In an application case where only the IN-P is used for 0-5 Vdc input, and correspondingly only use VO-P, when VOCM is tied to VSON, can the PGA281 be used? I realize that the VO-N will saturate low and cause an error flag; however the IN-N is not used ( i.e. tied to gnd or VSON as well).  I have a proto working this way now and I see no ill effects.  In the future I may change to a different amp and am considering the PGA206.

  • 0
    TI__Mastermind 27715 points

    Hello Steve,

    The minimum voltage applied to VOCM is (VSON) + 0.1V, so you are violating the data sheet minimum by shorting VOCM directly to VSON. The effects of this may be subtle, but you are likely placing the output stage into light saturation which will impact the linearity of the output. You may have a working prototype circuit, but we cannot guarantee that the design will be robust over temperature and process variations.

    Best regards,

    Ian Williams
    Linear Applications Engineer
    Precision Analog - Op Amps

  • 0 in reply to Ian Williams
    Prodigy 150 points

    Ian,

    Even with the VOCM set to 0.1v the -output will still saturate as the 0-5v input rises, as it will try to swing more negative and cannot.  Having to adjust VOCM up to allow for the -output to not saturate will greatly limit the output range ( i.e. 2.5 to 5V ) of the other output.  In another post I believe you stated it was ok to have VOCM grounded as long as the input did not go negative.  For single-ended applications it seems this amp limits you to 1/2 the normal range.  Would the PGA206 be a better fit?  BTW, I am running full thermal characterization on the grounded VOCM now and will evaluate the performance.  I am doing a multi-nomial surface fit of the data to correct for non-linearity, gain, and any other repeatable error. 

     

  • 0 in reply to SteveKK
    TI__Mastermind 27715 points

    Hi Steve,

    The PGA206 would be a more straightforward device to configure as it's designed for a single-ended output, unfortunately, it's about 4x more expensive and has poorer precision. If you fully characterize the PGA281 in your current configuration and are content with its performance, it would be the more efficient option.

    Best regards,

    Ian Williams