C8051F850-C-GM Datasheet, PDF (106/328 Pages) Silicon Laboratories – Low-Cost 8-bit MCU Family with up to 8 kB of Flash

14.9. Temperature Sensor
An on-chip temperature sensor is included, which can be directly accessed via the ADC multiplexer in
single-ended configuration. To use the ADC to measure the temperature sensor, the ADC mux channel
should select the temperature sensor. The temperature sensor transfer function is shown in Figure 14.8.
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. While disabled, the temperature
sensor defaults to a high impedance state and any ADC measurements performed on the sensor will result
in meaningless data. Refer to the electrical specification tables 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 14.8. Temperature Sensor Transfer Function
14.9.1. Calibration
The uncalibrated temperature sensor output is extremely linear and suitable for relative temperature
measurements. 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 ADC input.
4. Calculate the offset characteristics, and store this value in non-volatile memory for use with
subsequent temperature sensor measurements.
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