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PGA280 Divider Question

ClayCope
Prodigy 60 points
Other Parts Discussed in Thread: PGA280

I do have one technical issue that’s keeping me from moving forward with the PGA280.  The 1/8 gain isn’t small enough to get the input range that I need.  We have to support a +/-10V range, which means that we need to have a measurement range that’s +/-11V.  With 1/8 gain, I get 1.375V, but my reference is 1.25V.  I can’t find a 1.5V reference, so I’m wondering if I can put a divider on the output of the PGA280.  My thought is to put a resistor divider from VOP to VON, probably in the 10k-20k range.  Would this be the best solution, or is there a better one?  Does adding a resistor divider compromise the performance of the PGA280 (other than the obvious drift of the external resistors?)

  • 0
    Prodigy 60 points

    I received an answer through another channel but thought I'd post it here for everyone else. 

    Your suggestion, dividing down the output voltage between VOP and VON is perfect.

    Depending on the next stage (is it a SigDel converter ?) the resistor values should perhaps be somewhat lower.

    Assuming 1.4V to be divided down to 1.25V you could use 2x 300ohms and 5k.

    The resistors add their gain drift, as you already mention. 

    Using attenuation at the output has the advantage of dividing down errors (and noise) of the PGA with the same ratio as the signal.

     

  • 0 in reply to ClayCope
    TI__Genius 11830 points

    Clay,

    Thank you for posting the answer here as well!  You rock!