The GPADC channels are calibrated in the production line using a two-point calibration method. The channels are measured with two known values (X1 and X2) and the difference (D1 and D2) to the ideal values (Y1 and Y2) are stored in OTP memory. The principle of the calibration is shown in Figure 6-10.
Some of the GPADC channels can use the same calibration data and the corrected result can be calculated using the equations:
If the measured code is a, the corrected code a' is:
Table 6-4 summarizes the parameters X1 and X2, and the register of D1 and D2 needed in the calculation for all the channels.
|0,1||2064 (0.63 V)||3112 (0.95 V)||GPADC_TRIM1||GPADC_TRIM2||Channel 1 trimming is used|
|2||2064 (1.26 V)||3112 (1.9 V)||GPADC_TRIM3||GPADC_TRIM4|
|7||2064 (2.52 V)||3112 (3.8 V)||GPADC_TRIM7||GPADC_TRIM8|