C8051F80X_14 Datasheet, PDF (58/251 Pages) Silicon Laboratories – Mixed Signal ISP Flash MCU Family

C8051F80x-83x
9. Temperature Sensor
An on-chip temperature sensor is included on the C8051F800/1/2/3/4/5, C8051F812/3/4/5/6/7,
C8051F824/5/6, and C8051F830/1/2 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 be
configured to connect to the temperature sensor. The temperature sensor transfer function is shown in
Figure 9.1. 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 10.1. 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 7.11 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 9.1. Temperature Sensor Transfer Function
9.1. Calibration
The uncalibrated temperature sensor output is extremely linear and suitable for relative temperature mea-
surements (see Table 5.1 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 ADC’s input.
4. Calculate the offset characteristics, and store this value in non-volatile memory for use with subsequent
temperature sensor measurements.
Figure 5.3 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 temper-
ature measurement.
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