AN4207 datasheet(20/28 Pages) STMICROELECTRONICS

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Application examples

AN4207

20/28

Doc ID 023945 Rev 1

The temperature measurement is performed in two steps:

Temperature sensor calibration: this phase is performed with JP18 fitted in 2-3(REF)

position. A 100 Ohm resistor is connected to PE7 which is connected to VREF through

the reference resistor. The SDADC converter measures the analog voltage applied on

PE7 and then computes the correction coefficient. This calibrates the gain. The PT100

is not connected in this phase.

Temperature measurement: this phase is performed with JP18 fitted in 1-2 (PT100)

position. The PT100 sensor is connected to PE7 which is connected to VREF through

the reference resistor. The SDADC converter measures the analog voltage applied on

PE7 and then computes the temperature which is given by the following formula:

TemperaturePT100 = (((((CoeffCorrection * (AvrgRegularConvData/SDADC_GAIN) *

REFERENCE_RESISTOR * 2) / SDADCRESOL) - RESISTANCE_ZERODEGRE) /

RESISTANCE_COEFFICIENT);

where:

AvrgRegularConvData is the average value of 256 samples

SDADC_GAIN is the internal SDADC gain. In this example it is set to 8

CoeffCorrection is the correction coefficient computed in phase 1.

REFERENCE_RESISTOR is the reference resistor 1K8 labeled R33 on STM32373C-

EVAL

SDADCRESOL is the sigma delta converter: 2e16-1

RESISTANCE_ZERODEGRE is the resistance of PT100 at 0 °C

RESISTANCE_COEFFICIENT is the coefficient of PT100 sensor

Table 5.

Temperature sensor voltage range

VDD = 3.3V

Temperature

Resistance (

)

Voltage (mV)

Rref = 1.8 K

0 °

100

91.667

20°

107.7

98.725

50 °

119.2

109.2667

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