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INA2141: Non-Ideal Characteristics

Thomas Relling
Prodigy 50 points
Part Number: INA2141
Other Parts Discussed in Thread: TLE2064, INA141, INA826,

We are using the INA2141U as a differential amplifier in a test system. The test limits for different load configurations are 36.4uA +/- 20% and 3.6uA +/- 50%.  I am trying to understand why we allow such a large tolerance when the voltage out of the TLE2064 is controlled to +/- 1% and the load resistance tolerance is +/- 1%.

 

What are the input offset voltage characteristics for the INA2141U? Could this be the reason for the wide specifications?  Do you have any articles explaining how the INA2141U output varies from ideal and what are the causes of the variation?  Ideally, with I_LOAD = 3.6uA the voltage at the input to the INA2141U is 144.7uV.  The output of the INA2141U should be 1.447mV.  With a tolerance of +/- 50%, we allow the voltage on Test Point J68 to vary from 1.447mV +/- 50%.  I am trying to understand why. 

 

The purpose of the circuit is to measure leakage current. In normal operating conditions I_LOAD could be 30mA so the voltage at J68 could reach 12.06V.INA2141 Circuit.pdf

  • 0
    TI__Mastermind 23050 points
    Hi Thomas,

    The dc characteristics of the INA141 are all specified in the datasheet. In a gain of 10 the maximum offset voltage of the part is +/-100uV. So with a 144.7uV input signal it is possible that yes, roughly half of what you measure is due to the offset voltage of the part. It sounds to me that this is likely why your limits are defined in this way. If you want to understand the different error sources and how to calculate the error, table 2 in the datasheet for the INA826 is a good reference.
  • 0
    TI__Guru 61340 points

    Thomas,

    You may easily get around this problem by calibrating out INA2141 initial offset error - this may be accomplished by first measuring the output voltage under zero current in R45 shunt resistor (for  Iload=0, Vout_cal=10*Vos) and then subracting Vout_cal from all Vout readings for various Iload magnitudes - see below:

  • 0 in reply to Marek Lis
    Prodigy 50 points

    Thank you Zak and Marek.  Your comments have been very helpful.