13.3.11 Temperature Sensor
An on-chip analog temperature sensor is available to the ADC multiplexer input. 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
ature Sensor Transfer Function on page 136
. 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 de-
faults 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.
Temperature
= (
Slope
x
) +
Offset
Offset
Slope
= (
-
Offset
) /
Slope
V
oltage
(V at 0 deg Celsius)
(V / deg C)
Temp
C
V
TEMP
V
TEMP
Temp
C
Figure 13.5. Temperature Sensor Transfer Function
13.3.11.1 Temperature Sensor Calibration
The uncalibrated temperature sensor output is extremely linear and suitable for relative temperature measurements. For absolute tem-
perature 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 meas-
urements.
Although more precision can be obtained by calibrating the temperature sensor in the end system, a single-point offset measurement of
the temperature sensor is performed on each device during production test. The measurement is performed at 25 °C ±5 °C, using the
ADC with the internal high speed reference buffer selected as the Voltage Reference. The direct ADC result of this measurement is
stored in the SFR registers TOFFH and TOFFL
EFM8SB2 Reference Manual
Analog-to-Digital Converter (ADC0)
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