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ADS8900B: Input offset

Yee Yong Teo
Expert 4335 points

Part Number: ADS8900B

Hi,

How do I relate figure 16. Offset vs Temperature (pg.14 of datasheet) to parameter Input offset thermal drift (Pg. 6 of datasheet)?

Thanks.

- YY

  • 0
    TI__Guru 55466 points

    Hi YY,

    There is a typographical error on page 6.  The expected offset drift performance is better than the specified: the drift performance is 1uV/C while the current datasheet lists 10uV/C.  The correct 1uV/C spec will be reflected in the upcoming datasheet revision, and should be posted on the web soon.

    Figure 16 shows the Offset vs temperature drift in LSBs (Least Significant Bits).  The ADS8900B is a 20-bit device.  While using VREF=5V, the Full-Scale Range (FSR) for the device is +/-VREF or +/-5V or 10V.  Therefore the bit weight is given by:

    LSB= FSR / 2^N or +/-5V/2^20 = 10V/2^20 = 9.53uV (where N is the bit resolution of the ADC)

    If we look at Figure 16, the offset drift can be calculated for a given temperature range.  For example:

    offset @ 26C is approximately -1.5LSBs or -1.5LSB*9.53uV = -14.3uV

    offset @ 59C is approximately +1 LSBs or +9.53uV

    Drift in this temperature range can be calculated as:

             Offset Drift (uV/C) = Change in Offset (uV) / Change in temperature (C)

    Offset Drift (uV/C) = (+9.53uV - (-14.3uV)) / (59C-26C)

    Offset Drift (uV/C) = 0.716uV/C

    This approximates the typical offset drift spec of 1uV/C


    I will follow up with this query directly via email.

    Thank you and Best Regards,

    Luis Chioye