NXP Semiconductors KL25 Series - Calibration Function

If the condition selected evaluates true, SC1n[COCO] is set.
Upon completion of a conversion while the compare function is enabled, if the compare
condition is not true, SC1n[COCO] is not set and the conversion result data will not be
transferred to the result register, Rn. If the hardware averaging function is enabled, the
compare function compares the averaged result to the compare values. The same compare
function definitions apply. An ADC interrupt is generated when SC1n[COCO] is set and
the respective ADC interrupt is enabled, that is, SC1n[AIEN]=1.
Note
The compare function can monitor the voltage on a channel
while the MCU is in Wait or Normal Stop modes. The ADC
interrupt wakes the MCU when the compare condition is met.
28.4.6 Calibration function
The ADC contains a self-calibration function that is required to achieve the specified
accuracy. Calibration must be run, or valid calibration values written, after any reset and
before a conversion is initiated. The calibration function sets the offset calibration value,
the minus-side calibration values, and the plus-side calibration values. The offset
calibration value is automatically stored in the ADC offset correction register (OFS), and
the plus-side and minus-side calibration values are automatically stored in the ADC plus-
side and minus-side calibration registers, CLPx and CLMx. The user must configure the
ADC correctly prior to calibration, and must generate the plus-side and minus-side gain
calibration results and store them in the ADC plus-side gain register (PG) after the
calibration function completes.
Prior to calibration, the user must configure the ADC's clock source and frequency, low
power configuration, voltage reference selection, sample time, and high speed
configuration according to the application's clock source availability and needs. If the
application uses the ADC in a wide variety of configurations, the configuration for which
the highest accuracy is required should be selected, or multiple calibrations can be done
for the different configurations. For best calibration results:
• Set hardware averaging to maximum, that is, SC3[AVGE]=1 and SC3[AVGS]=11
for an average of 32
• Set ADC clock frequency f
ADCK
less than or equal to 4 MHz
• V
REFH
=V
DDA
• Calibrate at nominal voltage and temperature
The input channel, conversion mode continuous function, compare function, resolution
mode, and differential/single-ended mode are all ignored during the calibration function.
Functional description
KL25 Sub-Family Reference Manual, Rev. 3, September 2012
494 Freescale Semiconductor, Inc.