ST STEVAL-IHT001V1, Руководство пользователя

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UM0277 Functional description
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2.3.2 ST7LITE39F2 microcontroller
The MCU used in the thermostat kit is the ST7LITE39F2. It belongs to the ST7LITE39F2
MCU family. It embeds a large number of features at the minimum cost. The peripheral
hardware requirements are then reduced to the minimum:
●
No crystal oscillator or external resonator is used. Indeed, the internal RC-oscillator of
the ST7LITE39F2 is used to generate the clock.
● No external RESET circuit is used, due to the internal circuit of the ST7LITE39F2.
In case of MCU firmware change, four options have to be set:
●
Software watchdog activation
● RC oscillator selection
●
PLL disabled
● Low Voltage Detection selection
2.3.3 Capacitive power supply
To reduce the board price as much as possible, a capacitive power supply is used on the
board. The maximum average current sunk by the board is about 30mA for 4ms gate current
pulse widths (see
Table 2 ). In this case, a 1µF C3 capacitor value should be used in order
for the board to work correctly under typical application conditions (nominal capacitor value,
230V RMS line voltage).
For higher or lower currents, the C3 capacitor can be changed. Table 3 lists the maximum
allowed average current versus the different C3 capacitor values for typical application
conditions (nominal capacitor value, 230 V
RMS
line voltage) and worst application case
(nominal C3 capacitor value -10%, 198 V
RMS
line voltage), for a 50Hz mains frequency.
For more information about the design of the capacitive power supply please refer to
Application Note AN1476.
Table 2. Maximum average current sunk by the board
Devices
Average current
consumption
Comments
MCU 2.5mA
Maximum supply current in Run Mode.
f
CPU
= 1MHz and V
DD
= 5.5V
LEDs 2.7mA
LEDs switch ON/OFF alternatively on each AC mains
polarity in order to reduce the current consumption.
V
F
= 1.6V @ I
F
= 4mA, V
DD_Max
= 5.5V and
R
9
= R
10
= R
11
= 750Ohms±1%
Gate average
current necessary
to control AC
switches
21mA
Switches Q1 (Compressor) and Q2 (Defrost) cannot be
switched ON at the same time. The gate average current is
only defined according to the Q2 (Defrost) and Q3 (Light
Bulb) gate current.
V
DD_Max
= 5.5V, R
DSON_MCU
= 25
Ω
, R
4
= 130
Ω
±5%,
R
5
= 390
Ω
±5% and 4ms gate currents pulses widths
Others (Push
Button, NTC
supply, Buzzer)
4.3mA
V
DD_Max
= 5.5V, R
NTC
@0°C = 16
Ω
, R
14
= 10k
Ω
±5% and
R
15
= 200
Ω
±5%
(I
Buzzer supply current
= 4mA)
Total 30.5mA