UM1542 datasheet(13/43 Pages) STMICROELECTRONICS

13 / 43 page

UM1542

Functional description

Doc ID 023172 Rev 1

13/43

The GUI provides the following features (refer to the “Help” menu of the GUI software for

more information):

●

Slide bars to change the MCU parameters (refer to Figure 7 and 8):

–

Temperature hysteresis

–

Evaporator temperature set point for each thermostat order

–

Gate current pulse widths and delays

–

Time before defrost activation and defrost duration

–

ZVS delay (synchronization of MCU commands with the mains voltage)

●

Virtual knob to set the evaporator temperature level

●

Virtual switch (“debug active”) to force the loads to on or off states (compressor, light,

defrost, fan) for easier board validation

●

Measurement and storage of several parameters during operation (duty cycle and

running period of the compressor, evaporator temperature evolution, mains frequency

and load status).

The most recently modified variables with the GUI can be stored for operation in standby

mode.

It can be noted from Figure 2 that the part of the PCB dedicated to the PC interface is

clearly separated from that part of PCB dedicated to thermostat control in order to easily

visualize the component count dedicated only to the thermostat application.

By means of opto-couplers, safety insulation is implemented between the board and the PC

to allow communication with the GUI when the board is plugged into the line voltage. These

opto-couplers, U3, U4, and U5 are supplied from the USB connector CN1 and the DC-DC

converter J1 in order to not sink current from the capacitive power supply (Appendix B).

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