UM1542 datasheet(9/43 Pages) STMICROELECTRONICS

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UM1542

Functional description

Doc ID 023172 Rev 1

9/43

Figure 3.

Hysteresis law

Five temperature set points have been implemented:

Very low

Low

Medium

High

Very high

For each temperature set point an evaporator temperature, a hysteresis, thus an upper limit

and a lower limit are defined. THIGH_lim and TLOW_lim are respectively the upper and the

lower limits of the hysteresis and are defined as:

Equation 1

Equation 2

The compressor is switched on if the sensed temperature is above THIGH_lim, and switched

off when this temperature becomes lower than TLOW_lim. When the door is open

(Section 2.2.3), temperature control is not allowed, i.e. any action on TEMP+ and TEMP-

has no effect. The temperature set point, or temperature order, can be set at one of the five

levels by means of the two push buttons PB1 and PB2 (temperature setting push buttons) in

standalone mode (see Figure 2) or by means of the GUI in PC-driven mode (Section 3.6),

while the hysteresis value can only be changed using the GUI.

Five LEDs - D4, D5, D6, D8, D9 (temperature setting LEDs) (Figure 2) in standalone mode,

or VL, L, M, H, VH in PC GUI driven mode (Figure 7) - turn on according to the temperature

set point.

lim

Hysteresis

Temperatur

Evaporator

HIGH

lim

Hysteresis

Temperatur

Evaporator

LOW

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UM1542 Datasheet(PDF) 9 Page - STMicroelectronics