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ADS117L11: Gain and Offset specification

Pascal Regache
Prodigy 140 points

Part Number: ADS117L11

Tool/software:

Hello,

I would appreciate a clarification on the Gain and Error specification of the ADS117L11.

Referring to the device datasheet, page 6, the top page says "minimum and maximum specifications apply from TA = –40°C to +125°C; typical specifications are at TA = 25°C".

So I guess that the +/-250µV offset error is applicable from T min to T max. Now taking the typical value (30µV) and taking into account the offset temperature drift of 200nV/°C max and considering a 100°C temperature increase, the offset would be 30µV + 0.2µV/°C * 100°C = 50µV. That is quite far from the 250µV specified as a min/max for the offset. Why is that ? And which number should I use then ?

The point is that the numbers are quite different and using the specified max (250µV) may result in over-constraining my design if the actual value is 5x lower; and I need to know the offset value at a different operaing temperature than the +125°C.

Same question applies to the gain specification, but I guess the answer will be the same as for the offset.

Thank you

Best regards

Pascal

  • 0
    TI__Guru 51130 points

    Hello Pascal,

    The offset and gain errors can vary quite a bit over wafer lots, which is why the min/max is much higher.  This includes both process shift and worst case temperature shifts.  If you do not plan to do any kind of system calibration, then you need to use the min/max spec of 250uV for offset and 2000ppm for gain.

    For best accuracy, calibrate both offset and gain, and then the primary error source remaining will be the temperature drift.  Assuming you calibrate at 25C for both gain and offset, then the remaining maximum offset error will be 20uV and remaining maximum gain error will be 200ppm, or 0.02%.

    Since external amplifiers and reference can also contribute to total system error, calibration of the entire signal chain including the ADC will eliminate a large percentage of the error.

    Regards,

    Keith Nicholas
    Precision ADC Applications