C8051T630 Datasheet, PDF (45/221 Pages) Silicon Laboratories – Mixed-Signal Byte-Programmable EPROM MCU

C8051T630/1/2/3/4/5
7. Temperature Sensor (C8051T630/2/4 only)
An on-chip temperature sensor is included on the C8051T630/2/4 which can be directly accessed via the
ADC multiplexer. To use the ADC to measure the temperature sensor, the ADC mux channel should be
configured to connect to the temperature sensor. The temperature sensor transfer function is shown in
Figure 7.1. The output voltage (V_TEMP) is the positive ADC input when the ADC multiplexer is set correctly.
The TEMPE bit in register REF0CN enables/disables the temperature sensor, as described in SFR Defini-
tion 9.1. While disabled, the temperature sensor defaults to a high impedance state and any ADC mea-
surements performed on the sensor will result in meaningless data. Refer to Table 5.10 for the slope and
offset parameters of the temperature sensor.
V_TEMP = (Slope x Temp_C) + Offset
Temp_C = (V_TEMP - Offset) / Slope
Slope (V / deg C)
Offset (V at 0 Celsius)
Temperature
Figure 7.1. Temperature Sensor Transfer Function
7.1. Calibration
The uncalibrated temperature sensor output is extremely linear and suitable for relative temperature mea-
surements (see Table 5.10 on page 29 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 production test. The registers TOFFH and TOFFL, shown in SFR Defini-
tion 7.1 and SFR Definition 7.2 represent the output of the ADC when reading the temperature sensor at 0
degrees Celsius, and using the internal regulator as a voltage reference.
Figure 7.2 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.
Rev. 1.0
45