Note
There is an effective limit to the values of offset that can be set
by the user. If the magnitude of the offset is too high, the results
of the conversions will cap off at the limits.
The offset calibration function may be employed by the user to remove application
offsets or DC bias values. OFS may be written with a number in 2's complement format
and this offset will be subtracted from the result, or hardware averaged value. To add an
offset, store the negative offset in 2's complement format and the effect will be an
addition. An offset correction that results in an out-of-range value will be forced to the
minimum or maximum value. The minimum value for single-ended conversions is
0x0000; for a differential conversion it is 0x8000.
To preserve accuracy, the calibrated offset value initially stored in OFS must be added to
the user-defined offset. For applications that may change the offset repeatedly during
operation, store the initial offset calibration value in flash so it can be recovered and
added to any user offset adjustment value and the sum stored in OFS.
33.4.8 Temperature sensor
The ADC module includes a temperature sensor whose output is connected to one of the
ADC analog channel inputs.
The following equation provides an approximate transfer function of the temperature
sensor.
m
Figure 33-93. Approximate transfer function of the temperature sensor
where:
• V
TEMP
is the voltage of the temperature sensor channel at the ambient temperature.
• V
TEMP25
is the voltage of the temperature sensor channel at 25 °C.
• m is referred as temperature sensor slope in the device data sheet. It is the hot or cold
voltage versus temperature slope in V/°C.
For temperature calculations, use the V
TEMP25
and temperature sensor slope values from
the ADC Electricals table.
Functional description
K22F Sub-Family Reference Manual , Rev. 3, 7/2014
732
Freescale Semiconductor, Inc.
