C8051F99X_10 Datasheet, PDF (84/322 Pages) Silicon Laboratories – Ultra Low Power, 8-2 kB Flash, Capacitive Sensing MCU

C8051F99x-C8051F98x
5.8.1. Calibration
The uncalibrated temperature sensor output is extremely linear and suitable for relative temperature mea-
surements (see Table 4.11 for linearity specifications). For absolute temperature measurements, offset
and/or gain calibration is recommended. Typically a 1-point (offset) calibration includes the following steps:
1. Control/measure the ambient temperature (this temperature must be known).
2. Power the device, and delay for a few seconds to allow for self-heating.
3. Perform an ADC conversion with the temperature sensor selected as the positive input and
GND selected as the negative input.
4. Calculate the offset characteristics, and store this value in non-volatile memory for use with
subsequent temperature sensor measurements.
Figure 5.9 shows the typical temperature sensor error assuming a 1-point calibration at 25 °C. Parame-
ters that affect ADC measurement, in particular the voltage reference value, will also affect temper-
ature measurement.
A single-point offset measurement of the temperature sensor is performed on each device during produc-
tion test. The measurement is performed at 25 °C ±5 °C, using the ADC with the internal high speed refer-
ence buffer selected as the Voltage Reference. The direct ADC result of the measurement is stored in the
SFR registers TOFFH and TOFFL, shown in SFR Definition 5.13 and SFR Definition 5.14.
5.00
5.00
4.00
4.00
3.00
3.00
2.00
2.00
1.00
1.00
0.00
0.00
-40.00
-20.00
0.00
40.00
60.00
80.00
20.00
-1.00
-1.00
-2.00
-2.00
-3.00
-3.00
-4.00
-4.00
-5.00
-5.00
Temperature (degrees C)
Figure 5.9. Temperature Sensor Error with 1-Point Calibration (V_REF = 1.65 V)
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