ADS9817: difference between output data and measured data

Hi,

There are 2 questions.

1. There is difference between output data and measured data

What point does customer check for this issue?

Test condition:

-Calibration Register ( GE_CAL_EN1,2,3) Disable

-ADC CH -> REF35120 (1.2 V Reference IC)

Measured Data (DVM 0.025% Accuracy) : 1.1999~1.2001 V

Output Data (ADS9817) : 1.1708~1.179 V

2. Could you explain GE_CAL_EN1, 2, 3?

3. What purpose is GE_CAL_EN and when customer control it?

4. at USER_GAIN_CAL_CH, could you explain the equation of gain data control? ex) data for gain=1