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OPA1632 Offset température drift

Michel ROHR
Prodigy 50 points
Other Parts Discussed in Thread: OPA1632, INA333, INA826

Hello,

I Will use an OPA1632 on as input amplifier for an analog to digital converter board. OPA1632 offset temperature drift is +/-5µV/°C. Is this drift stable on a chip ? Target is to calibrate my board over temperature range 0-55°C. Can this offset drift be corrected by a calibration ?

Thanks

Michel

  • 0
    TI__Guru 64840 points

    Michel,

    OPA1632 offset drift typical spec of +/-5uV/C represents +/-1-sigma of Normal Gaussian Distribution as shown below.  This means that 1 out of 3 units will have a drift greater than 5uV/C (1-sigma), 1 out of 370 units will have a drift greater than 15uV/C (3-sigma), 1 out of 1,744,277 units will have a drift greater than 25uV/C (5-sigma), etc. at least for the temperature range from -40C to 85C (for worst case analysis, I would assume the same drift for 0C to 50C.)

    With time, all PDS specs undergo a slow long-term shift and this include an input offset drift.  The blue bell-shape curve on the above graph (to the right) represents an initial distribution of drift while the green curve shows the same units after 10 years in the field - the maximum drift may shift by the maximum initial value.  Since in case of OPA1632, there is no PDS maximum drift spec, you need to use statistical means to set a relative maximum value; for example, if you will accept that 1 out 22 units may be outside of such maximum limit, +/-2-sigma or +/-10uV/C maximum shift should be used.  This means that a unit with an initial drift of +10uV/C may become +20uV/C or 0uV/C (+10uV/C+/-10uV/C) while another unit with initial drift of -5uV/C may become +5uV/C or -15uV/C (-5uV/C+/-10uV/C).

    The initial offset drift can be calibrated out by measuring a change in the input offset voltage of each unit over desired temperature range BUT there is no way to calibrate the long-term drift since it is a random shift that is not a function of the initial drift - the only way would be to periodically calibrate the individual units as they age.

  • 0 in reply to Marek Lis
    Prodigy 50 points

    Hello,

    Thanks for your answer.

    Have you an other fully differential amplifier to recommend me with a very small long time temperature offset drift. On owner application, we use this amplifier to measure voltage (0 - 400Hz)  on a current sensor resistor (<0.2Ohm).

    Best regards

    Michel

  • 0 in reply to Michel ROHR
    TI__Guru 64840 points

    Michel,

    For a low supply voltage, 1.8V<Vs<5.5V, please consider INA333 with the maximum input offset drift of +/-0.1uV/C +/-(0.5uV/C)/G where G is a gain used.  In case of higher supply voltage, 2.7V<Vs<36V, please take a look at INA826 with the maximum input offset drift of +/-2uV/C.