Calibration; Figure 9.2. Toffh And Toffl Calibration Value Orientation; Figure 9.3. Temperature Sensor Error With 1-Point Calibration At 0 Celsius - Silicon Laboratories C8051T620 Manual

C8051T620/1/6/7 & C8051T320/1/2/3

9.1. Calibration

The uncalibrated temperature sensor output is extremely linear and suitable for relative temperature mea-
surements (see Table 7.11 on page 41 for specifications). For absolute temperature measurements, offset
and/or gain calibration is recommended.
A single-point offset measurement of the temperature sensor is performed on each device during produc-
tion test. The TOFFH and TOFFL calibration values represent the output of the ADC when reading the
temperature sensor at 0 degrees Celsius, and using the internal regulator as a voltage reference. The
TOFFH and TOFFL values can be read from EPROM memory and are located at 0x3FFB (TOFFH) and
0x3FFA (TOFFL). The temperature sensor offset information is left-justified, so TOFFH contains the 8
most-significant bits of the calibration value and TOFFL.7-6 contain the 2 least-significant bits of the cali-
bration value, as shown in Figure 9.2. One LSB of this measurement is equivalent to one LSB of the ADC
output under the measurement conditions.
TOFFH
Bit 7 Bit 6 Bit 5 Bit 4
10-bit Temperature Sensor Offset Calibration Value

Figure 9.2. TOFFH and TOFFL Calibration Value Orientation

Figure 9.3 shows the typical temperature sensor error assuming a 1-point calibration at 0 °C. Parameters
that affect ADC measurement, in particular the voltage reference value, will also affect temperature
measurement.
5.00
4.00
3.00
2.00
1.00
0.00
-40.00
-1.00
-2.00
-3.00
-4.00
-5.00

Figure 9.3. Temperature Sensor Error with 1-Point Calibration at 0 Celsius

58
Bit 3 Bit 2 Bit 1 Bit 0
-20.00 0.00
Temperature (degrees C)
Rev. 1.2
TOFFL
Bit 7 Bit 6 Bit 5 Bit 4
20.00 40.00
Bit 3 Bit 2 Bit 1 Bit 0
5.00
4.00
3.00
2.00
1.00
0.00
60.00 80.00
-1.00
-2.00
-3.00
-4.00
-5.00