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Characterization of VOS for the LMH6703

Jose Delgado
Prodigy 225 points
Other Parts Discussed in Thread: LMH6703

How did National Semi characterize VOS on the LMH6703 for the datasheet?  Was the measurement taken from the output or was it taken from the negative pin?  If it was taken from the negative pin, how did you all manage to keep the part from oscillating?  Is the VOS measurement calculated and not measured?

Thanks for your response,

Jose D

  • 0
    TI__Mastermind 22825 points

    Hello,

    With the LMH6703 put in a closed loop configuration, the offset test could consist of an instrumentation amplifier (IA) across the device inputs. The IA offset itself (measured by placing a short across the IA inputs) is then subtracted from the measured IA output. LMH6703 offset would be this number, divided by the IA gain.

    If tying / connecting anything to the inverting input causes oscillations, try isolating it from the inverting input by using a tightly-placed, low capacitance (surface mount) resistor (> 20ohm) between it and the LMH6703. You can do that with a high impedance device like an IA, especially if all you are interested in is low frequency or DC information.

    Hope this helps.

    Hooman

  • 0 in reply to Hooman Hashemi
    Prodigy 225 points

    Hooman,

    Thanks for your help.  I tried the easiest of the the 2 suggestions being that I am working on a PCB, but the resistor value on the negative input to the DMM had to be above 500 ohms.  Fix the problem with the resistor.  I am able to take DC measurements.