38.5.14.1 Calibration Mode of Operation
The ADC is built to convert positive and negative voltages around a common mode voltage (ADVREFP-GNDIN33)/2. This is why the ADC output, averaging and calibration are performed as 2's complements. An ADC positive integer output is generated only in the last stage to generate unsigned data.
The ADC code is first averaged when requested; calibration is applied afterward. See the following figure.
Three internal reference voltages, VM, VL and VH, are generated from ADVREFP, with:
- VL = (ADVREFP-GNDIN33)x(1/16)
- VH = (ADVREFP-GNDIN33) x(15/16)
- VM = (ADVREFP-GNDIN33)/2
In Single mode non-signed outputs, the references are ideally converted as:
- VL_code = 256
- VH_code = 3840
- VM_code = 2048
In Differential mode signed outputs, the references are ideally converted as:
- (VL-VH)_code = -1792
- (VH-VL)_code = +1792
- VM_code = 0
The difference between the two voltage reference codes is the value 3584.
For calibration, three values are measured using ADCMODE 1,2,3.
In the table ADC Running Modes, ConvValue is the current converted value.