AN3397

Temperature sensor application description

Doc ID 018809 Rev 1

13/24

Normal mode

Normal mode is the default mode configured in the software example. In this mode, the blue

LED (see Figure 2) is switched off.

To activate this mode, comment the following define statement in the main.c file of the TS

application code:

// #define ADVANCED_MODE

In Normal mode, the temperature is processed from default (typical) values of Avg_slope

and sensor reference voltage at 90 °C (V90) which are available in the STM8L15xxx

datasheets.

Avg_slope = 1.62 mV/°C

V90 = 0.597 V

This method has certain advantages. It is straightforward and the measurement is rapidly

obtained as it does not require the calculation of a second calibration point. However, data

which are statically based on the typical characteristics of the TS, may provide less accurate

temperature estimations due to significant variations of the temperature characteristics

during the manufacturing process. If an application needs very accurate measurements, it is

better to use the Advanced operating mode described below.

Advanced mode

To activate advanced mode, uncomment the following define statement in the main.c file of

the TS application code:

#define ADVANCED_MODE

When this mode is selected, the blue LED (see Figure 2) is switched on.

In advanced mode, V90 is obtained precisely by reading the TS factory calibration byte:

TS_Factory_CONV_V90. This byte represents the 8 LSB of the result of the V90 12-bit ADC

conversion (see STM8L15xxx datasheet). The MSB have a fixed value: 0x3.

The advantage of using this result is to get a more precise V90 value which consequently

leads to greater precision when measuring the temperature. To further reduce the error, it is

recommended to define another calibration point at ambient temperature to accurately

define the average slope parameter and the offset. This TS application code (user

calibration point) implements a technique to obtain and store this user calibration (see

Section 2.4.3: Calibration technique) and consequently gives a more precise temperature

slope. The average slope is accurately calculated from the user and factory calibration data

Equation 6

Before proceeding to perform the user calibration, the factory calibration data point is tested

for validity when the application is initialized. If the factory calibration data point is present in

the memory @0x4911, it is used for temperature calculation. Otherwise, the user calibration

procedure is bypassed and the application automatically switches back to normal mode.

Advanced method is more difficult to implement and has more constraints but, it gives more

precise results.

Avg_slope

V

 T





V90

V

AMBIENT

–

 T90 T

–





==