ST STEVAL-IHM020V1, User Manual, Page: 10 / 23

Features UM0583
10/23
3 Features
3.1 ST7LITE39F2 microcontroller
The 8-bit MCU used in this board is the ST7LITE39F2. It belongs to the ST7 family of
microcontrollers, and offers a large number of features at minimum cost.
●
The peripheral hardware requirements are reduced to a minimum:
– No quartz or external resonator is used. Instead, an internal RC-oscillator in the
ST7LITE3 is used to generate the clock
– No external RESET circuit is used
● In the MCU firmware, four options must be set:
– Software watchdog activation
– RC oscillator selection
– PLL disabled
– Low voltage detection selection
Note: The MCU firmware has been developed only to evaluate the STCC08 device and is not
compliant with the class B (IEC60335-1 Ed4) requirements.
3.2 DC capacitive power supply
A DC capacitive power supply is used on the board. One peculiarity of this DC power supply
is that it is “negative”. The V
CC
terminal is connected to neutral. This means that the GND
voltage is 5 V below neutral. Such a connection is mandatory to drive the ACS. Indeed, the
ACS can only be triggered by a negative current (i.e. sourced from the gate). The maximum
average current absorbed by the board is about 44 mA (see
Table 3 ). In this case, a 2.2 µF
C16 capacitor value has been used to ensure that the board works correctly in the worst
application conditions (230 V/110 V
RMS
line voltage ± 10% and V
CC
± 10%).
Note that a 43.2
Ω
R
IG
resistor (R23) value is used. In this case, the minimum ambient
temperature must be 0 °C in order to work correctly the board. For lower ambient
Table 3. Maximum average current sunk by the board
Device
Average
current
consumption
Comments
MCU 2.5 mA Maximum supply current in run mode. F
CPU
=1 MHz and V
CC
=5.5 V
LEDs (two LEDs maximum
can be ON at the same time)
15 mA
LED STCC08 controlled
LEDs visualizing the ACS failure
R
19
=R
20
= R
21
= R
22
=475
Ω
± 1%
Maximum current consumed
by STCC08 (include the gate
current of the ACS)
26 mA
V
CC_MAX
=5.5 V, temperature = 0° C
R
IG
= 43.2 ± 1% (R23)
Others (mechanical switch) 0.5 mA V
CC_Max
=5.5 V
Total 44 mA
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