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Ts321 diffirential apa proportionality factor has a big deviation for different boards???

user3707938
Prodigy 50 points
Other Parts Discussed in Thread: TS321

as below schematics, resistor is 1% tolorance.

Ts321 diffirential apa proportionality factor: K= V0_REF/10_GND=  47/220= 0.2136. but proportionality factor: K   has a big deviation for different boards, about +/-3% deviation; why?? how to improve this?

  • 0
    TI__Guru*** 149776 points

    Here is a simulation schematic using an ideal op amp and ideal resistors.

    VOUT is 2.13636363636363V

     

    By changing just R1 +/-1% gives this result

    R1

    VOUT

    Error

    46530

    2.217097378

    3.78%

    47000

    2.136363636

    0.00%

    47470

    2.055629894

    -3.78%

     

    Looking at gain for the 10V input gives the same result

    R1

    Gain

    Error

    46530

    0.221709738

    3.78%

    47000

    0.213636364

    0.00%

    47470

    0.205562989

    -3.78%

     

    Here is VIO spec for TS321

     

    Error due to VIO is VIO* R1/R4 +1  < +/-5mV * (47k/20k +1) = 6.07mV; this is a DC offset error in addition to all other error sources.