UM0277 datasheet(6/32 Pages) STMICROELECTRONICS

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Functional description

UM0277

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Functional description

2.1

Performances

This board meets the following requirements:

●

Medium-end appliances: this thermostat board can control the loads traditionally used

in medium-end cold appliances (compressor, light, defrost resistor).

●

Electromagnetic Compatibility: the board is able to withstand bursts of more than 2.3kV

during IEC61000-4-4 standard tests without any operational problems (and up to 4.5kV

without any damage). Surge tests have also been performed (IEC61000-4-5 standard):

2 kV bursts can be applied without any damage for the semiconductors.

●

Safety standards have also been taken into account. A 2-mm creepage is ensured

between all high voltage parts and low voltage parts (to achieve the functional

insulation level). The (NTC) thermistor is a class II sensor, and can be put on non-

earthed accessible and conductive parts.

2.2

Ensured functions

2.2.1

Temperature control

The thermal sensor used is an NTC thermal resistor (thermistor) from EPCOS (M2020 5 k

2%). It should be placed on the evaporator of the fridge or the freezer. The controlled

evaporator temperature range should be between -20 and 5 °C. The range can be modified

by changing the value of the resistor placed in series with the NTC (refer to Appendix A).

The NTC resistance value decreases, following an exponential variation, when the

temperature increases. Then, to get back the temperature data, the MCU could use a

numerical table. In the STEVAL-IHT001V1 board, a simple resistor has been added in

series with the NTC in order to linearize its thermal response (refer to Appendix A). Two

advantages come from this choice:

●

Memory area savings

●

Easy way to measure the temperature.

Temperature regulation is achieved by Hysteresis control (see Figure 3).

Figure 3.

Hysteresis law

UM0277 Datasheet(PDF) 6 Page - STMicroelectronics