dm00210549

AN4732
Application note
STCOMET smart meter and power line communication
system-on-chip development kit
Patrick Guyard, Riccardo Fiorelli, and Johann Houee
Introduction
The EVLKSTCOMET10-1 is a development kit for the STCOMET platform, exploiting the
performance capability of the full-feature STCOMET10 device. The STCOMET10 is a single
device integrating a flexible power line communication (PLC) modem with a fully embedded
analog front end (AFE) and a line driver, a high performance 3-channel metrology function
and a Cortex ™ -M4 application core.
The kit is made of three modules: the STCOMET main board, the LCD module and the
power supply board based on the VIPER26H.
With this development kit, it is possible to evaluate a complete single phase smart meter
with PLC connectivity. The performance of the metering and application functions could be
evaluated along with the PLC transmitting and receiving performance.
The PLC line coupling interface is designed to allow the STCOMET device to transmit and
receive on the AC mains line using any narrow-band PLC modulation (single carrier or
OFDM) up to 500 kHz, mainly for automatic meter reading (AMR) applications.
The default configuration of the PLC line coupling targets the G3-PLC (ITU G.9903) and
PRIME (ITU G.9904) CENELEC A-band protocol standards. With a few BOM modifications,
the STCOMET development kit can be adjusted to fit other narrow-band PLC protocols in
CENELEC A-band or FCC band (e. g.: S-FSK IEC61334-5-1, IEEE 1901.2, G3-PLC FCC,
METERS AND MORE®).
If necessary, a specific customer's module can be designed and placed instead of the LCD
module, for a different peripherals configuration.
As it can be seen from the EVLKSTCOMET10-1 picture, a special effort has been made to
create the development kit compact and optimized to fit the size of a real meter.
The EVLKSTCOMET10-1 is suitable for the evaluation of the complete STCOMET platform.
Featuring the full set STCOMET10 chip, the EVLKSTCOMET10-1 demonstrates at the
same time all the functions and performance of the STCOM chips.
Please check for the EVLKSTCOMET10-1 hardware documentation, evaluation software
and firmware libraries at st.com/powerline. For specific software or firmware releases, you
may need to contact directly the STMicroelectronics sales office.
Figure 1. STCOMET10 development kit (EVLKSTCOMET10-1)
October 2015
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Contents
AN4732
Contents
1
Safety recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2
STCOMET smart meter and power line communication
system-on-chip description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3
STCOMET development kit description . . . . . . . . . . . . . . . . . . . . . . . . . 8
4
STCOMET development kit electrical characteristics . . . . . . . . . . . . . . 9
5
IMPORTANT - STCOMET development kit use and safety . . . . . . . . . 10
6
7
5.1
USB connectors CN2 and CN3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.2
Low voltage connection mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
5.3
Isolated mains connection mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
5.4
Non-isolated mains connection mode . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
Using the STCOMET development kit . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.1
Silabs CP2105 driver installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.2
Segger J-Link driver installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.3
Connection procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.4
Development tool usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.5
Evaluation tool usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Evaluating with PLC GUI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.5.2
Evaluating metrology features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
STCOMET main board description . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
7.1
Power supply configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
7.2
Power line interface section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7.3
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6.5.1
7.2.1
Line driver network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
7.2.2
Line coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
7.2.3
Reception filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7.2.4
Zero crossing coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Metrology section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
7.3.1
Metrology circuit description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
7.3.2
Three-phase metrology evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
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Contents
7.4
Line breaker section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
7.5
STCOMET I/O section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
7.5.1
STCOMET system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
7.5.2
STCOMET GPIOs mapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
7.5.3
STCOMET Flash SPI0 and EEPROM interfaces . . . . . . . . . . . . . . . . . 34
7.5.4
STCOMET UART0 and UART1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
7.5.5
STCOMET tamper inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
7.5.6
STCOMET JTAG interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
7.5.7
General purpose push buttons and LEDs . . . . . . . . . . . . . . . . . . . . . . . 34
8
LCD module description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
9
EN50065 compliance tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
10
Design guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
10.1
11
PCB layout guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
10.1.1
PCB structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
10.1.2
Design for thermal performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
10.1.3
Ground connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
10.1.4
Power supply connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
10.1.5
Mains voltage routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
10.1.6
Metrology connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
10.2
Oscillator section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
10.3
Power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
FAQ and troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
11.1
FAQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
11.2
Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
12
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
13
Normative references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
14
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
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List of tables
AN4732
List of tables
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6.
Table 7.
Table 8.
Table 9.
Table 10.
Table 11.
Table 12.
Table 13.
Table 14.
Table 15.
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Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Power supply configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Line driver parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Line coupling transformer specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Zero crossing coupling configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Zero crossing isolated coupling - measured timing characteristics. . . . . . . . . . . . . . . . . . . 23
Zero crossing non-isolated coupling - measured timing characteristics . . . . . . . . . . . . . . . 24
Zero crossing through metrology coupling - measured timing characteristics . . . . . . . . . . 27
Three-phase metrology evaluation - SPI/UART configuration . . . . . . . . . . . . . . . . . . . . . . 29
Line breaker driver - GPIO control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
STCOMET main board - system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
GPIO assignment table for the STCOMET development kit. . . . . . . . . . . . . . . . . . . . . . . . 31
List of standard tests required for EMC compliance to EN50065 - A-band
PLC applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
STCOMET main board PCB data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
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AN4732
List of figures
List of figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
Figure 17.
Figure 18.
Figure 19.
Figure 20.
Figure 21.
Figure 22.
Figure 23.
Figure 24.
Figure 25.
Figure 26.
Figure 27.
Figure 28.
Figure 29.
Figure 30.
Figure 31.
Figure 32.
Figure 33.
Figure 34.
Figure 35.
Figure 36.
Figure 37.
STCOMET10 development kit (ELVKTSTCOMET10-1). . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
STCOMET block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
STCOMET development kit - functional block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
STCOMET development kit - main connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Connecting the STCOMET development kit to a PC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
STCOMET board drawing with indication of the various sections . . . . . . . . . . . . . . . . . . . 15
STCOMET development kit with single 15 V DC supply . . . . . . . . . . . . . . . . . . . . . . . . . . 16
STCOMET development kit - power supply input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Single DC supply mode configuration - 3V3 generation . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
STCOMET development kit - line driver section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
STCOMET development kit - line coupling and reception filter section . . . . . . . . . . . . . . . 19
STCOMET development kit - zero crossing coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Measured line driver frequency response. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Isolated zero crossing coupling - positive edge delay . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Isolated zero crossing coupling - negative edge delay . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Non-isolated zero crossing coupling - positive edge delay . . . . . . . . . . . . . . . . . . . . . . . . . 25
Non-isolated zero crossing coupling - negative edge delay . . . . . . . . . . . . . . . . . . . . . . . . 25
STCOMET development kit - metrology section. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Zero crossing through metrology coupling - positive edge delay . . . . . . . . . . . . . . . . . . . . 28
Zero crossing through metrology coupling - negative edge delay . . . . . . . . . . . . . . . . . . . 28
Three-phase metrology evaluation - digital connections to STPMxx evaluation boards. . . 29
Default boot switch configuration (normal boot mode) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
LCD module drawing with indication of the various sections . . . . . . . . . . . . . . . . . . . . . . . 35
STCOMET package - bottom view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
PCB dissipating area on top layer for the STCOMET development kit board . . . . . . . . . . 39
PCB dissipating area on bottom layer for the STCOMET development kit board . . . . . . . 40
Internal layers under STCOMET package (L2 = left, L3 = right) for thermal dissipation
on STCOMET development kit board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Star GND connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Serial GND connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
GNDs connections on STCOMET development kit board . . . . . . . . . . . . . . . . . . . . . . . . . 43
Power supply distribution via tracks and copper planes . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Creepage and clearance isolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Tracks subject to specific isolation (1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Tracks subject to specific isolation (2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
GND connection for metrology voltage measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Dedicated tracks for voltage measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
EMI input filter for the VIPER26H power supply module . . . . . . . . . . . . . . . . . . . . . . . . . . 48
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Safety recommendations
1
AN4732
Safety recommendations
The STCOMET development kit must be used by expert technicians only. Due to the high
voltage (85 - 265 V ac) present on the non-isolated parts, special care must be taken in
order to avoid electric risks for people safety.
There are no protections against high voltage accidental human contact.
After disconnection of the board from the mains all the live part must not be touched
immediately because of the energized capacitors.
It is mandatory to use a mains insulation transformer to perform any tests on the high
voltage sections, using test instruments like, for instance, spectrum analyzers or
oscilloscopes.
Do not connect any probe to high voltage sections if the board is not isolated from the mains
supply, in order to avoid damaging instruments and demonstration tools.
When configured for metering evaluation, the STCOMET development kit is not isolated and
ground will be tied to the line. Do NOT connect instrument probes that can bring the earth
connection to the line, thus potentially damaging the STCOMET development kit and the
instruments and creating electrical risk.
STMicroelectronics assumes no responsibility for the consequences of any improper use of
this development tool.
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2
STCOMET smart meter and power line communication system-on-chip description
STCOMET smart meter and power line
communication system-on-chip description
The STCOMET is a device that integrates a narrow-band power line communication
(NB-PLC) modem, a high-performance application core and metrology functions.
The PLC modem architecture has been designed to target the EN50065, FCC, ARIB
compliant PLC applications. Together with the application core, it enables the STCOMET to
support the PRIME, G1, G3, IEEE 1901.2, METERS AND MORE and other narrow-band
PLC protocol specifications.
The metrology sub-system is suitable for the EN 50470-1, EN 50470-3, IEC 62053-21, IEC
62053-22 and IEC 62053-23 compliant class1, class0.5 and class0.2 AC metering
applications.
For further details, please refer to 1. in Section 12 on page 52.
Figure 2. STCOMET block diagram
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STCOMET development kit description
3
AN4732
STCOMET development kit description
The STCOMET development kit is available as a board set comprising:

One STCOMET main board

One LCD module with access to STCOMET GPIOs

One power supply unit based on VIPER26H
The functional block diagram is depicted in Figure 3.
Figure 3. STCOMET development kit - functional block diagram
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4
STCOMET development kit electrical characteristics
STCOMET development kit electrical characteristics
Table 1. Electrical characteristics
Value
Parameter
Notes
Min.
AC mains input frequency
Typ.
Max.
50/60
AC mains input voltage
Unit
Hz
J6 connector
J6 connector
90
230
440
V rms
Single DC input voltage
12
15
16
V
Single DC current capability
1
Single DC supply mode
A
J7 connector
VIPER26H power supply mode
VCC DC voltage
14
VCC DC current capability
700
5 V DC voltage
4.75
5 V DC current capability
100
3.3 V DC voltage
3.1
3.3 V DC current capability
200
15
16
V
mA
5
5.25
V
mA
3.3
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J13 connector
V
mA
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IMPORTANT - STCOMET development kit use and safety
5
AN4732
IMPORTANT - STCOMET development kit use and
safety
There are several ways to use the STCOMET development kit, with different levels of
safety. It is very important for the user to understand the related precautions to take for each
mode.
Figure 4 gives an overview of the paths used by the line and neutral high voltage on the
STCOMET development kit.
Figure 4. STCOMET development kit - main connections
5.1
USB connectors CN2 and CN3
Whatever the connection mode selected by the user, the USB connections at the CN2 and
CN3 remain isolated, allowing usage of the user's computer also in non-isolated
configuration.
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5.2
IMPORTANT - STCOMET development kit use and safety
Low voltage connection mode
For this configuration, no mains voltage is present. The STCOMET development kit must be
supplied through the J7 connector, using an isolated DC supply (15 V typ.) (see Section 7.1
on page 16).
The HW configuration will be as follows:

The VIPER26H power supply is OFF and can be removed

PLC communication can be done through the J6 connector without mains presence

The zero crossing for PLC can be provided only by the 50 Hz low voltage signal applied
to the STCOMET ZC_IN pin (ZC test point on main board)

Metrology tests can be done only with low voltage/current signals applied to the
metrology input pins.
This mode is recommended for SW-FW development or any activity outside of a safe
laboratory.
5.3
Isolated mains connection mode
Mains voltage is applied to the J6 only.
In this configuration, line and neutral voltages are present only in the “PLC-PSU main area”
highlighted in Figure 4, limited to the primary sides with respect to the PLC and PSU
transformers.
The rest of the STCOMET development kit remains isolated.
In this mode:
5.4

PLC communication can be done with presence of the mains voltage

Zero crossing for PLC can be provided through the isolated zero crossing coupling (see
Section 7.2.4 on page 22)

Metrology tests can be done only with low voltage/current signals applied to the
metrology input pins.
Non-isolated mains connection mode
Apply the mains line and neutral voltages to the J6, plus line to the R42 pin 3 (L_MTR) and
neutral to the J37.
In this mode:

The ground will be directly connected to line voltage

PLC communication can be done with presence of the mains voltage

Zero crossing for PLC can be provided through the isolated or non-isolated zero
crossing coupling circuits (see Section 7.2.4)

Full metrology tests can be performed. The mains load will be connected between the
R42 pin 1 (Lload_MTR) and neutral.
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Using the STCOMET development kit
6
AN4732
Using the STCOMET development kit
Figure 5. Connecting the STCOMET development kit to a PC
6.1
Silabs CP2105 driver installation
In order to connect an STCOMET development kit to the PC, install Virtual COM Port drivers
for the SiLabs CP2105 device (which converts data between the PC USB port and
STCOMET UART0 and UART1).
The latest drivers are available at:
http://www.silabs.com/products/mcu/Pages/SoftwareDownloads.aspx
The LEDs DL5 to DL8 show the UART TX and RX activity.
6.2
Segger J-Link driver installation
For FW JTAG development, a Segger J-Link on-board debugger has been included, with an
isolated USB interface to the PC for safe connection even when connecting to the mains.
The latest drivers are available at:
http://www.segger.com/jlink-software.html
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6.3
Using the STCOMET development kit
Connection procedure
The following procedure is required for every node to be connected to the PC:
1.
6.4
Verify that the mini USB cable for the UART (and optionally the one for JTAG access) is
connected to the PC
2.
Power up the STCOMET development kit
3.
Verify that the Virtual COM Ports (and J-Link driver if connected) have been installed.
Development tool usage
The STCOMET development kit has been conceived as a development platform to develop
and test any customer's solution based on the STCOMET device.
The STCOMET main board is widely configurable and allows different HW configurations,
for the GPIOs, PLC line coupling and metrology sensors.
6.5
Evaluation tool usage
In addition to use as a development platform, the STCOMET development kit can be used
in an application oriented evaluation environment. To do so, isolated USB connections to
the PC must be used.
6.5.1
Evaluating with PLC GUI
A typical PLC evaluation environment is composed by two or more STCOMET development
kits connected to one or more PCs running a protocol-related GUI which manages the
communication services offered by the STCOMET PLC FW.
6.5.2
Evaluating metrology features
In addition to the PLC evaluation, the user can control the metrology section of the
STCOMET through a dedicated GUI accessing the STCOMET registers for configuration
and measurement data reading.
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54
STCOMET main board description
7
AN4732
STCOMET main board description
The STCOMET main board is composed of the following sections:

STCOMET device section
–
Serial non-volatile memories
–
Boot mode configuration via DIP switches
–
24 MHz and 32 kHz oscillators
–
Decoupling capacitors

RTC backup battery

Line coupling section, including four subsections:

–
Configuration network for the integrated line driver
–
Reception filter
–
Power line coupling
–
Zero crossing coupling
Metrology section
–
Shunt connection on the line
–
Current transformer (CT) for the neutral
–
Voltage measurement (line - neutral)

Line breaker driver section

On-board power supply:

–
Configuration jumpers
–
Embedded regulator for single DC supply mode
JTAG debug section
–

2 UARTs over isolated USB
–

14/54
J-Link on-board accessible via isolated USB
Enhanced and standard COM ports
Module interface connector.
DocID028042 Rev 2
AN4732
STCOMET main board description
Figure 6. STCOMET board drawing with indication of the various sections
The board has also the following external connections or control:

AC mains (line and neutral) on J6 connector

Line breaker connector J5 to control external relay

Reset button and LEDs

Configuration jumpers.
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54
STCOMET main board description
7.1
AN4732
Power supply configuration
The STCOMET development kit includes the VIPER26H power supply board. However, for
convenient use without applying the mains voltage (mainly for software development) the
STCOMET main board could be used without the VIPER26H power supply. In that case, the
STCOMET main board can be supplied with an external 15 V DC source (see Figure 7).
Note that the external supply jack connector shall have 15 V on the internal contact and
GND on the external shield.
Figure 7. STCOMET development kit with single 15 V DC supply
Specific jumper configuration has to be set properly as shown in Table 2 and Figure 8.
Table 2. Power supply configuration
Configuration
Jumper reference
16/54
VIPER26H power supply mode
Single DC supply mode
J9
Close 2 - 3
Close 1 - 2
J10
Close 2 - 3
Close 1 - 2
J15
Close
Open
J16
Open
Close
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AN4732
STCOMET main board description
Figure 8. STCOMET development kit - power supply input
3V3_JACK
J30
J27
1
2
CLOSE 3V3_AUX
22-28-4023
J31
J11
3V3_PSU
N28
R59
22K
3V3
N29
CLOSE 3V3
22-28-4023
VCC_JACK
J10
J13
BLM31PG330SN1
VCC
5V
DL1
RED
3V3
DL2
RED
DL3
RED
VCC_PSU
CLOSE 3-2
22-28-4033
1
2
3
4
Place the x3 inductors near STCOMET
2
N30
VCC
L4
3
3V3
GND
VCC
5V
R61
2.2K
1
J28
R60
4.7K
L3
3
PSU
connector
3V3_PSU
5V_PSU
N27
J9
CLOSE 3-2
22-28-4033
VCC_PSU
3V3_AUX
J8
VCC
J29
42376 / 22-28-6040
CON-MOLEX-42376-H-4
Connector: correct orientation
to be respected by EMS
J15
TP6
1
N32
L5
5V
CLOSE
22-28-4023
1V2
N31
BLM31PG330SN1
5V_PSU
5V
External 1V2 supply possibility
1V2
KEYSTONE-5000
KEYSTONE5000
N33
BLM31PG330SN1
AM039705
In the single DC supply mode configuration, the whole STCOMET main board and LCD
module are supplied from the single 15 V DC supply using the following circuitry:
Figure 9. Single DC supply mode configuration - 3V3 generation
SUPPLY FROM BLA CK BOX
R56
If possible, add GND plane
on bottom layer
D13
1
2
3
NEB 21 R
15 W - 200 mA
U3
R57
1
75R
STTH102A
R58
75R
N26
C39
10UF
VIN
VOUT
3
3V3_JACK
3V3 jack
C37
4
J7
VCC_JACK
GND
NP
100NF
L4931CDT33
N25
C38
2.2UF
AM039707
The diode D13 prevents from revert voltage applied at the J7 level by mistake. VCC_JACK
is then the voltage applied to the STCOMET VCC.
The STCOMET 3.3 V is generated with the LDO U3. The 2 resistors R57 and R58 allow to
dissipate a portion of the power in order to relieve U3.
The STCOMET 5 V is generated by the 5 V regulator integrated in the STCOMET (pin 53),
using the jumper J16 closed.
This is absolutely not an optimized power scheme but it allows generating the necessary
supply voltages for safe SW development with low cost components and a reduced PCB
size.
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54
STCOMET main board description
7.2
AN4732
Power line interface section
The line coupling section is composed of four different sub-sections: the line driver
(Figure 10), the line coupling, the reception filter (Figure 11), and the zero crossing coupling
(Figure 12).
Both transmission and reception paths are fully differential, allowing for the higher dynamic
range and noise immunity.
The frequency response of this section is usually sensitive to tolerance of component
values. Actual components used in the STCOMET development kit have the following
tolerances: ± 20% for the X1 capacitor and the coils, ± 10% for SMD ceramic X7R
capacitors, and ± 1% for SMD resistors.
For the line driver, C0G/NPO type capacitors are required to guarantee linearity and stability
against signal amplitude and frequency.
Figure 10. STCOMET development kit - line driver section
C1
C2
27PF
4.7PF
VCC
CAP CER 100nF 50V X7R 0603
VCC
C5
C3
CAP CER 100nF 50V X7R 0603
100NF
100NF
TX -
TX-
CLOSE
22-28-4023
R2
2.00K
6.8K
R4
47K
J34
J2
R1
C14
100NF
PA2_INN PA2
C8
R5
VCM2
VCC
R6
47K
C7
JP1
22UF
SHORT
TRANSFORMER_1_S2
CLOSE
22-28-4023
PA2_INP +
0R
100NF
D1
STPS1L30A
PA-
J1
PA2_OUT
C6
1UF
J32
R3
47K
D2
STPS1L30A
R7
47K
C121
NP
R8
PA2_OUT
Cl osest to IC
NP
N1
R9
NP
VCC
J33
J3
C10
1UF
D3
STPS1L30A
PA+
C12
JP2
22UF
SHORT
TRANSFORMER_1_S1
CLOSE
22-28-4023
D4
STPS1L30A
VCC
VCC
CAP CER 100nF 50V X7R 0603
C13
100NF
CAP CER 100nF 50V X7R 0603
J35
R10
47K
C15
TX +
CLOSE
22-28-4023
R11
47K
R12
VCM1
PA1_INP
0R
100NF
C122
NP
R13
47K
PA1
PA1_INN
PA1_OUT
PA1_OUT
N2
-
TX+
+
J4
C4
100NF
R14
47K
C16
100NF
R15
R16
2.00K
6.8K
C17
C18
27PF
4.7PF
CAP CER 27pF 50V COG 0603
Cl osest to IC
AM039703
18/54
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AN4732
STCOMET main board description
Figure 11. STCOMET development kit - line coupling and reception filter section
C19
JP3
7
TRANSFORMER_1_S2
D5
NP
4
10
R18
0R
R19
0R
R21
49.9R
R22
49.9R
1
JP4
OPEN
SM6T10CA
L_PLC
Footprint
options
TRANSFORMER_1_S2
4
TRANSFORMER_1_S1
1
5
PRI
8
N
T1-2
TRAFO-WE-750-510-231
D9
SMAJ15CA
C24
10NF
470uH
CLOSE
C119
C22
CLOSE
L8
NP
L2
L7
CLOSE
JP6
OPEN
N
JP5
OPEN
L6
For Single ended
N_PLC
SIOV1
B72214S0321K101
T1
TDK SRW13EP-X05H002
D8
SM6T10CA
680nF
D6
SM6T18CA
U
R17
NP
NP
C20
L1
PRI
10uH
7447714100
TRANSFORMER_1_S1
D7
OPEN
C120
C23
10NF
C25
10NF
CLOSE
RX_INN
10NF
C26
RX_INP
10NF
JP7
OPEN
AM039704
Figure 12. STCOMET development kit - zero crossing coupling
ZCI: zero crossing ISOLATED coupling
ISO1
R27
33K
33K
N7
NOTE:
Place parts above close to Main inputs
3
R26
R25
100K
2
N_PLC
1
33K
STTH1L06A
R24
TLP781(GB)
3V3_AUX
1.00K
C27
100NF
R28
47K
TP1
TP
R29
10M
C28
100NF
1
R23
4
N5
D10
L_PLC
ZC
JP8
SHORT
ZCNI: zero crossing
NON-ISOLATED coupling
R207
R30
R31
NP
220K
220K
JP9
OPEN
N_ZC_UNINSULATED
D11
MM3Z3V0C
NOTE:
Place both resistor close to Main inputs
AM039708
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STCOMET main board description
7.2.1
AN4732
Line driver network
The line driver sub-section is based on the STCOMET internal dual power amplifier (PA),
whose input and output pins are externally available to allow configurability of the circuit.
The line driver amplifies the differential transmitted signal generated by the STCOMET
through the integrated current DAC and pre-driver.
The STCOMET line driver has very high linearity, so in this development kit it has been used
in all-pass configuration.
In the frequencies of interest, the capacitors C1, C2 and C5 have negligible impedance with
respect to the R1 and R2, so the in-band amplifier gain can be calculated as:

B
d
3
1
=
4
.
4
X
T
 
21
R R
1
G
Equation 1
The C5 is used to set the DC gain of the filter to 0 dB (input bias and output bias voltages
must be both VCC/2), while the C1 and C2 provide gain compensation by reducing the gain
at high frequencies.
Table 3. Line driver parameters
Symbol
Parameter
Value [typ]
Unit
|GTX|
In-band voltage gain
13
dB
BW3dB
Low-pass 3-dB bandwidth
5
MHz
Figure 13. Measured line driver frequency response
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AN4732
7.2.2
STCOMET main board description
Line coupling
The coupling to the power line requires a few passive components. In particular, it includes
the DC decoupling capacitors C7 and C12, the line transformer T1, the power inductor L1
and the X1 safety capacitor C20.
The L1 has been accurately chosen to have a high saturation current (> 2 A) and very low
equivalents series resistance (< 0.1 ), to limit distortion and insertion losses even with
a heavy line load.
Center frequency for the series resonance can be calculated at first approximation as:

0
2

C
1 L
'1
π
2
c
f
Equation 2
where L1 is the series of the L1 and the leakage inductance of the coupling transformer T1,
adding about 1 µH to L1.
The Q factor of this coupling circuit is driven by the mains line impedance: the choice of the
L1 and C20 values, anyway, leads to limited attenuation due to either parasitic impedance
or resonance selectivity.
Particular attention has been paid in choosing the line transformer. The required
characteristics are listed in Table 4. In order to have a good signal transfer and minimize the
insertion losses, it is recommended to choose a transformer with a primary (shunt)
inductance of 0.5 mH or greater, a leakage inductance much smaller than L1 and total DC
resistance lower than 0.5 .
Table 4. Line coupling transformer specifications
Parameter
Value
Turn ratio
1:1
Shunt inductance
≥ 0.5 mH
Leakage inductance
≤ 1.5 µH
DC total resistance
≤ 0.5 
DC saturation current
≥ 15 mA
Inter-winding capacitance
< 30 pF
Withstanding voltage
≥ 4 kV for double insulation
≥ 1.5 kV for functional insulation
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54
STCOMET main board description
7.2.3
AN4732
Reception filter
The reception filter in its default configuration is a simple band-pass filter made of resistance
in series with a parallel L-C resonant. The center frequency and the quality factor of the filter
can be expressed as:
Equation 3
where:
RL is the DC series resistance of the inductor (for example, with L2 = 744045471,
RL = 14.2  max).
The quality factor and the filter selectivity depend mainly on the value of (R21 + R22). Lower
value leads to lower steepness of the resonance, while higher value gives higher selectivity.
RL value may impact insertion losses. To evaluate the relationship between the RL and the
received signal loss, the following simplified expression can be used:
Equation 4
With actual values of the components, the transfer gain is almost unitary at center
frequency.
By looking to the transfer function formula, it can be noticed that a higher Q can help
keeping the losses small, but a high Q would also bring a higher sensitivity of the filter to
components tolerance.
7.2.4
Zero crossing coupling
The zero crossing coupling circuit is aimed at providing a bipolar (AC) signal synchronous
with the mains network voltage to the ZC_IN pin. This signal must be centered on AGND
and limited to less than 10 V pp.
Two ZC mode options are possible on the PLC side: isolated or non-isolated. The selection
is made through a few components, as indicated in Table 5.
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AN4732
STCOMET main board description
Table 5. Zero crossing coupling configuration
Reference
Isolated configuration
(default)
Non-isolated configuration
R207
Open
0
R26
33 k
Open
JP8
Close
Open
JP9
Open
Close
The isolated zero crossing circuit is realized through an optocoupler in non-inverting
configuration. Neutral and phase lines are brought to the optocoupler through 3 x 33 k
resistors in series, as represented in Figure 12 on page 19. The STTH1L06A diode blocks
the negative half-wave, thus reducing the circuit power consumption by half. The 3 x 33 k
resistors limit the photodiode input current to nearly 2 mA rms at 230 V AC. Having several
resistors helps preventing short-circuits in case of resistor degradation.
The timing characteristics of this circuit, according to the oscilloscope screenshots reported
below, are listed in Table 6.
Table 6. Zero crossing isolated coupling - measured timing characteristics
Edge
ZC delay
ZC jitter
Positive
232 µs
4 µs
Negative
4.8 µs
3 µs
Figure 14. Isolated zero crossing coupling - positive edge delay
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54
STCOMET main board description
AN4732
Figure 15. Isolated zero crossing coupling - negative edge delay
A second option is to use non-isolated zero crossing, for BOM cost reduction. In the circuit
implemented in the STCOMET development kit, the MM3Z3V0C Zener diode clamps the
input mains voltage to +3.0 and -0.7 V, while the two 220 k series resistors limit the Zener
current during conduction.
The timing characteristics of this circuit, according to the oscilloscope screenshots reported
below, are listed in Table 7.
Table 7. Zero crossing non-isolated coupling - measured timing characteristics
24/54
Edge
ZC delay
ZC jitter
Positive
2.8 µs
3.3 µs
Negative
18 µs
2.5 µs
DocID028042 Rev 2
AN4732
STCOMET main board description
Figure 16. Non-isolated zero crossing coupling - positive edge delay
Figure 17. Non-isolated zero crossing coupling - negative edge delay
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STCOMET main board description
7.3
AN4732
Metrology section
The STCOMET integrates the metrology function, which includes a 3-channel AFE with
24-bit sigma-delta converters and a dedicated DSP. The STCOMET implements all the
features needed for a single-phase energy meter, providing effective measurement of the
active and reactive energy, V rms, I rms, instantaneous voltage and current.
In the STCOMET development kit, the three metrology input channels are mapped as
follows (see Figure 18):

Channel METR_VP / METR_VN for measuring the mains voltage

Channel METR_IP / METR_IN for measuring the current through a shunt sensor

Channel METR_AP / METR_AN for measuring the current through a current
transformer sensor.
Figure 18. STCOMET development kit - metrology section
N50
H3
N_ZC_UNINSULATED
2ND VO LT
R34
NP
N49
J37
NEUTRAL
1
2
R35
NP
3
4
R36
270K
8191-7
R37
NP
R39
U1H
94
93
N15
C32
22NF
R44
470R
L_METR
METR_IP
METR_IN
METR_VP
METR_VN METR_AP
METR_AN
91
92
C29
10NF
C31
4.7NF
N16
R43
1.00K
89
90
10NF
COPPER
L_METR
CP3
H1
N18
1.00K
C33
L_LOAD_METR
R42
0.3mR
LINE
R45
IC-STCOMET10
N17
LINE LOAD
SHUNT 1
R40
240K
R41
NP
N14
1.00K
C30
4.7NF
2
3
R38
270K
R46
6.04R
H2
CT
T2
T60404-E4626-X002
N19
R48
1.00K
Near COMET and
over M_GND plane
R50
0R
Near COMET and
over M GND plane
AM039709
Mains connections are illustrated in Figure 4 on page 10.
The metrology LED0 and LED1 on the LCD module (Figure 23 on page 35) are blinking
according respectively to the cumulative active power and reactive power.
The STCOMET metrology features can be evaluated by using a dedicated GUI.
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AN4732
7.3.1
STCOMET main board description
Metrology circuit description
Current measurement
Anti-aliasing filters are implemented between the shunt, current transformer and the
STCOMET for distortion reduction caused by sampling.
Voltage measurement
A resistor divider is used as a voltage sensor. The 780 k resistor is separated into four in
series 1% resistors (270 k, 270 k, 240 k, 470 ), which ensure robustness against
a high voltage transient. This also reduces the potential across the resistors, thereby
decreasing the possibility of arcing.
The STCOMET kit also allows to use the channel METR_AP / METR_AN for a second
voltage measurement if necessary, for example to monitor the mains voltage after the line
breaker. The following BOM modifications must be applied in that case:

R34 = 620 k

R35 = R37 = 470 k

R41 = R45 = R48 = 0 

R50 = 470 

C33 = 22 nF.
Metrology zero crossing
The metrology section is including a built-in metrology zero crossing, independent from PLC
zero crossing information. This zero crossing signal is based on voltage applied at
METR_VP / METR_VN inputs, and can be made available on the STCOMET GPIO06_7 or
GPIO09_5 pin.
In principle, it is possible to connect the metrology zero crossing output to ZC_IN input for
the PLC section, by adding a 1 µF series capacitor to the ZC_IN and a 1 M resistor (not
present on the board) between the ZC_IN pin and AGND, with the JP8 = JP9 = open in this
case. Please note that in this use case the delay on PLC zero crossing information is much
higher, reaching about a quarter of the mains period.
The timing characteristics of the metrology zero crossing signal, according to the
oscilloscope measurements on GPIO09_5 reported below, are listed in Table 8.
Table 8. Zero crossing through metrology coupling - measured timing characteristics
Edge
ZC delay
ZC jitter
Positive
4.95 ms
27 µs
Negative
4.94 ms
31 µs
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54
STCOMET main board description
AN4732
Figure 19. Zero crossing through metrology coupling - positive edge delay
Figure 20. Zero crossing through metrology coupling - negative edge delay
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AN4732
7.3.2
STCOMET main board description
Three-phase metrology evaluation
The STCOMET development kit provides an SPI/UART interface (J2 connector) and
general purpose signals (J3 connector) on the LCD module (Figure 23) to connect STPMxx
metrology boards in order to build a three-phase meter development kit.
Figure 21 reports the J2 and J3 pinout plus the configuration jumpers to select between the
UART and SPI connection to the external STPMxx board. Table 9 describes the jumper
configuration to select SPI or UART configuration.
Figure 21. Three-phase metrology evaluation - digital connections to STPMxx evaluation boards
3V3_AUX
METR3P_MOSI
METR3P_MISO
METR3P_SCLK
METR3P_SYN
3V3_AUX
2
4
6
8
10
J2
J34
R50
NP
1
3
5
7
9
J15
GPIO10_4
METR3P_SS
METR3P_MOSI
SPI
GPIO10_6
R53
CON_5x2
CLOSE
22-28-4023 J37
J36
METR3P_SCLK
CLOSE
22-28-4023
0R
J35
METR3P
3V3_AUX
METR3P_INT2
METR3P_EN/RST
METR3P_CKOUT
OPEN
22-28-4023
3V3_AUX
R58
10K
J3
2
4
6
8
USART
R59
10K
1
3
5
7
METR3P_INT1
METR3P_LED2
METR3P_LED1
METR3P_CKIN
GPIO09_3
0R
CON-4x2
R65
1.5K
LED1
R63
DL3
RED
R66
1.5K
DL4
RED
LED2
AM039710
Table 9. Three-phase metrology evaluation - SPI/UART configuration
Jumper
SPI configuration
UART configuration
J15
Close
Open
J35
Open
Close
J36
Close
Open
R50
NP
1 k
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54
STCOMET main board description
7.4
AN4732
Line breaker section
The STCOMET development kit allows controlling a line breaker relay for remote electrical
disconnection. The circuit is based on the ST L2293Q driver, see the datasheet for
additional information.
An external voltage supply VR (0 - 36 V max.) must be applied between the J5 pin 4 (GND)
and J5 pin 3 (+) as coil driving voltage. The value of the VR must be in agreement with the
coil rating.
The line breaker coil must be connected between J5 pins 1 and 2.
The STCOMET GPIOs GPIO00_0 and GPIO00_1 allow to control the voltage applied to the
relay coil according to Table 10.
l
Table 10. Line breaker driver - GPIO control
GPIO00_0
GPIO00_1
VRA (J5 pin 2) VRB (J5 pin 1)
Function
H
L
VR
GND
Turn ON
L
H
GND
VR
Turn OFF
L
L
GND
GND
Keep state (zero current)
H
H
VR
VR
Keep state (zero current)
The J5 is a MOLEX male connector, P/N 22-27-2041. It is designed to be plugged with the
female connector MOLEX P/N 22-01-2045.
7.5
STCOMET I/O section
On the STCOMET main board, the I/O section provides the following features:
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
External access through several interface types: USB, SPI, I2C, USART, JTAG, CAN

Use up to 86 GPIOs

Control LCD display

Use up to 6 ADC channels

Control STPMxx extension boards for three-phase metering

Manage tamper events

Manage metrology LEDs
DocID028042 Rev 2
AN4732
7.5.1
STCOMET main board description
STCOMET system
Basic system control of the STCOMET device is listed in Table 11.
Table 11. STCOMET main board - system
Connection
Connection
STCOMET pins
type
Notes
Reset
Digital
74
Complete reset of the system (push button for
reset)
JTAG
Digital
18, 20, 21, 19,
22
Connected to the Segger J-Link OB section (see
Section 6.2 on page 12)
BOOT MODE
Digital
BOOT0 pin 15
BOOT1 pin 17
Define boot mode as specified in 1. of Section 12
on page 52
Configured via DIP switches
The default boot configuration is the normal boot mode (BOOT1 = 1, BOOT0 = 0), as
depicted in Figure 22.
Figure 22. Default boot switch configuration (normal boot mode)
7.5.2
STCOMET GPIOs mapping
The STCOMET has 86 GPIOs assigned to specific function, as listed below. All GPIOs are
connected to the strip connectors on the LCD module and clearly identified on the PCB
silkscreen.
Table 12. GPIO assignment table for the STCOMET development kit
GPIO
Description
Connection
GPIO00_0
RELAY_A external relay command
L2293Q on main board
GPIO00_1
RELAY_B external relay command
L2293Q on main board
GPIO00_2
Not used
GPIO00_3
Not used
GPIO00_4
Not used
GPIO00_5
Not used
GPIO00_6
I2C0_SDA EEPROM data
EEPROM on main board
GPIO00_7
I2C0_SCL EEPROM clock
EEPROM on EVBSTCOMET
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STCOMET main board description
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Table 12. GPIO assignment table for the STCOMET development kit (continued)
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GPIO
Description
GPIO01_0
Not used
GPIO01_1
UART1_TXD
CP2105 on main board
GPIO01_2
UART1_RXD
CP2105 on main board
GPIO01_3
UART1_RTS
CP2105 on main board
GPIO01_4
UART1_CTS
CP2105 on main board
GPIO01_5
Not used
GPIO01_6
Not used
GPIO01_7
Not used
GPIO02_0
Not used
GPIO02_1
Not used
GPIO02_2
Not used
GPIO02_3
Not used
GPIO02_4
Not used
GPIO02_5
Not used
GPIO02_6
Not used
GPIO02_7
Not used
GPIO03_0
Backlight LCD on LCD module
GPIO03_1
Not used
GPIO03_2
LCD_R/Wn
LCD on LCD module
GPIO03_3
LCD_EN
LCD on LCD module
GPIO03_4
LCD_SPI3_MOSI
LCD on LCD module
GPIO03_5
LCD_RS
LCD on LCD module
GPIO03_6
LCD_SPI3_SCLK
LCD on LCD module
GPIO03_7
LCD_SPI3_SS
LCD on LCD module
GPIO04_0
LCD_D0
LCD on LCD module
GPIO04_1
LCD_D1
LCD on LCD module
GPIO04_2
LCD_D2
LCD on LCD module
GPIO04_3
LCD_D3
LCD on LCD module
GPIO04_4
LCD_D4
LCD on LCD module
GPIO04_5
LCD_D5
LCD on LCD module
GPIO04_6
METR_CMD1
Button on LCD module
GPIO04_7
METR_CMD2
Button on LCD module
GPIO05_0
Not used
GPIO05_1
Not used
GPIO05_2
Not used
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LCD on LCD module
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STCOMET main board description
Table 12. GPIO assignment table for the STCOMET development kit (continued)
GPIO
Description
GPIO05_3
Not used
GPIO05_4
Not used
GPIO05_5
UART0_RTS
CP2105 on main board
GPIO05_6
UART0_CTS
CP2105 on main board
GPIO05_7
IRDA_SD
IrDA on LCD module
GPIO06_0
UART3_TXD
IrDA on LCD module
GPIO06_1
UART3_RXD
IrDA on LCD module
GPIO06_2
Not used
GPIO06_3
Not used
GPIO06_4
Not used
GPIO06_5
Not used
GPIO06_6
Not used
GPIO06_7
Not used
GPIO07_0
Not used
GPIO07_1
Not used
GPIO07_2
Not used
GPIO07_3
Not used
GPIO07_4
Not used
GPIO07_5
Not used
GPIO07_6
Not used
GPIO07_7
Not used
GPIO08_0
LED0_debug
LED0 on the main board
GPI08_1
LED1_debug
LED1 on the main board
GPIO08_2
LED2_debug
LED2 on the main board
GPIO08_3
LD3_debug
LED3 on the main board
GPIO08_4
Not used
GPIO08_5
Not used
GPIO09_0
METR3P_INT1
J3 METR3P on LCD module
GPIO09_1
METR3P_INT2
J3 METR3P on LCD module
GPIO09_2
METR3P_EN/RST
J3 METR3P on LCD module
GPIO09_3
METR_LED0
LED0 METR on LCD module
GPIO09_4
METR_LED1
LED1 METR on LCD module
GPIO09_5
Not used
GPIO09_6
METR3P_LED1
LED1 METR3P on LCD module
GPIO09_7
METR3P_LED2
LED2 METR3P on LCD module
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Table 12. GPIO assignment table for the STCOMET development kit (continued)
7.5.3
GPIO
Description
Connection
GPIO10_0
METR3P_CKOUT
J3 METR3P on LCD module
GPIO10_1
Not used
GPIO10_2
METR3P_SYN
J2 METR3P on LCD module
GPIO10_3
METR3P_MOSI
J2 METR3P on LCD module
GPIO10_4
METR3P_MISO
J2 METR3P on LCD module
GPIO10_5
METR3P_SCLK
J2 METR3P on LCD module
GPIO10_6
METR3P_SS
J2 METR3P on LCD module
GPIO10_7
Not used
STCOMET Flash SPI0 and EEPROM interfaces
The STCOMET SPI0 interface is connected to an external M25P16 16-Mbit SPI Flash for
the FW upgrade.
The I2C0 interface allows storing metrology or other application data into the M24512
EEPROM memory.
7.5.4
STCOMET UART0 and UART1
The STCOMET development kit provides two UARTs over the same isolated USB port
connector CN2:
7.5.5

UART0 corresponds to the Silabs CP2105 enhanced COM port

UART1 corresponds to the Silabs CP2105 standard COM port.
STCOMET tamper inputs
Two push buttons TPA and TPB, connected respectively to RTC_TAMPA and RTC_TAMPB,
are present on the LCD module to simulate tamper events.
7.5.6
STCOMET JTAG interface
The STCOMET development kit provides a debug JTAG interface via the J-Link on-board
over an isolated USB port connector CN3.
7.5.7
General purpose push buttons and LEDs
The STCOMET development kit provides a LCD display that could be used to develop
a meter application example. Two push-buttons P1 and P2 on the LCD module could be
used as inputs for a software application purpose (Figure 23).
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8
LCD module description
LCD module description
On the top of the STCOMET main board, the LCD module provides:

LCD display for metering and application information

LED0 and LED1 for energy measurement

TPA and TPB buttons to simulate tamper events

P1 and P1 buttons for any application menu (on LCD)

All GPIOs and ADC signals accessible thanks to strip connectors

Extension connectors plus 2 metering LEDs for three-phase metering configuration

IrDA interface
Figure 23. LCD module drawing with indication of the various sections
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EN50065 compliance tests
9
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EN50065 compliance tests
Table 13 lists all the EMC/EMI compliance tests required by the European standard
EN50065 for smart metering PLC applications on the low voltage network (which have the
highest EMC test levels).
All applicable tests have been carried out on the STCOMET development kit. Full EMC
compliance to the EN50065 part 1, 2 - 3 and 7 has been officially achieved with PRIME
A-band implementation, while successful pre-compliance tests have been carried out for
other PLC implementations.
All immunity tests require a communication link to be established between the equipment
under test (EUT) and a stimulus device. During such tests, the presence of
a communication is monitored to verify the acceptance criteria according to the specific test.
Table 13. List of standard tests required for EMC compliance to EN50065 - A-band PLC
applications
Type
Basic standard
Test
Result
PLC transmission:
Conducted measurement
EN 50065-1
Bandwidth measurements
PASS(1)
EN 50065-1
Maximum output levels
PASS(1)
Conducted disturbance
measurements
EN 50065-1, EN 55022
Conducted emissions (9 kHz - 30 MHz)
PASS(1), (2)
Radiated disturbance
measurements
EN 50065-1, EN 55022
Radiated emissions (30 MHz - 1 GHz)
PASS(2)
EN 61000-4-3
RF radiated fields immunity test (80 - 1000
MHz, 10 V/m)
PASS
Radiated immunity
Contact/radiated immunity
Conducted immunity
Input impedance
measurement
EN 61000-4-8
Magnetic 50 Hz field immunity test (100 A/m,
Not applicable
300 A/m)
EN 61000-4-2
Electrostatic discharges immunity test (8 kV
contact and air mode)
PASS(3)
EN 61000-4-6
RF conducted signals immunity test (150 kHz
- 80 MHz, 10 V rms)
PASS(3)
EN 50065-2-3
Narrow-band signals immunity test (95 kHz150 kHz; 150 kHz - 30 MHz)
PASS(3)
EN 61000-4-4
Fast transients immunity test (2 kV, 5 kHz)
PASS(3)
EN 61000-4-5
Surge immunity test (4 kV, common mode
and differential mode)
PASS(3)
EN 61000-4-11
Power voltage dips and interruption
(30% - 10 ms; 60% - 100 ms; 100% - 5 s)
PASS(2), (3)
RX impedance
PASS(1)
TX impedance
PASS(1)
EN50065-7
1. Related to specific PLC protocol implementation.
2. Results impacted by the VIPER26H power supply module.
3. In case of non-metering applications, communicating outside the CENELEC A-band, please refer to the immunity
requirements listed in the EN50065-2-1 document, which may set lower limits for some tests.
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Design guidelines
10
Design guidelines
10.1
PCB layout guidelines
10.1.1
PCB structure
The STCOMET main board PCB data are listed in Table 14.
Table 14. STCOMET main board PCB data
10.1.2
Parameter
Value
Number of layers
4
Laminate type or IPC-4101 categorization
FR4
Board thickness
1.60 mm
Base copper thickness (inner layers)
18 /1 8 µm
Finished copper thickness (outer layers)
35 / 35 µm
Size of PCB unit
115 x 128 mm
Design for thermal performance
The STCOMET device can operate within the standard industrial temperature range, from
-40 to 85 °C ambient temperature. Especially in high ambient temperature conditions, the
effect of the power dissipation of the device must be considered to keep it operating in safe
conditions.
Even if the STCOMET features thermal protection, the role of the PCB design to ensure
proper dissipation is the most important.
A TQFP176 package with an exposed pad (internally connected to DGND) has been
chosen for the STCOMET device to have a very good thermal performance. To take full
advantage from this, the PCB must be designed to effectively conduct heat away from the
package.
Figure 24. STCOMET package - bottom view
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To get a low impedance thermal path to the PCB, a 9.5 x 9.5 mm thermal pad has been
realized on the top layer under the device. In order to effectively remove the heat, the
exposed pad must be well soldered to the PCB thermal pad.
In order to have an effective heat transfer from the top layer of the PCB to the bottom layer,
thermal vias need to be included within the thermal pad area. If properly designed, thermal
vias are the most efficient paths for removing heat from the device.
The layout recommendations are therefore:
For the top layer:

Top layer function is to transmit heat from the package to the bottom layer

The DGND copper area must be placed under the exposed pad, extending as much as
possible around the device

An array of 9 x 9 thermal vias (top to bottom layer) at the 1.0 mm pitch, diameter
0.3 mm, shall be incorporated under the exposed pad, plus enough vias from the
DGND top plane to the bottom layer plane

Any unused area outside of the package must be filled with copper tied to the
dissipating DGND plane on the bottom layer.
For the bottom layer:
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
The bottom layer acts as the real radiator

The solid DGND area of copper on this layer must be as large as possible to minimize
the thermal impedance

To minimize solder wicking effect due to open vias, possibly leading to poor soldering of
the TQFP176 exposed pad, the via encroaching technique can be adopted. The bottom
side solder resist shall have small openings (nearly 0.2 mm larger than the via drill
diameter) around the vias; the reduced area of exposed copper on the bottom reduces
the amount of solder paste flowing down the vias

Traces on the bottom side must run as far as possible from the device area.
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Design guidelines
Figure 25. PCB dissipating area on top layer for the STCOMET development kit board
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Figure 26. PCB dissipating area on bottom layer for the STCOMET development kit board
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Design guidelines
On internal layers:
A large area under the STCOMET package must be dedicated to DGND, in order to
allow vias making the connection between top and bottom layers.
Figure 27. Internal layers under STCOMET package (L2 = left, L3 = right) for thermal dissipation
on STCOMET development kit board
10.1.3
Ground connections
The STCOMET system has 3 distinct ground references: analog (AGND) mainly for PLC,
metrology (MGND), and digital (DGND).
It is very important to filter each supply pin to its respective ground. Please refer to the
STCOMET datasheet for the association between each supply rail and the correct ground.
Good soldering of the STCOMET exposed pad (DGND) is also required to minimize ground
noise.
In addition, it is recommended to realize a star connection of the 3 ground planes at the
PCB level in order to guarantee good signal integrity. Figure 28 and Figure 29 illustrate what
are the benefits of such star topology.
Let's consider that GND tracks have not a null impedance but Z1, Z2, and Z3.
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Figure 28. Star GND connection
In Figure 28, the voltage offsets are limited to the following values:

DGND = GND + Z1 x ID

AGND = GND + Z2 x IA

MGND = GND + Z3 x IM
Figure 29. Serial GND connection
In Figure 29, we can see that each ground reference is shifted with the following voltage
offsets:
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
DGND = GND + Z1 x (ID + IA + IM)

AGND = GND + Z1 x (ID + IA + IM) + Z2 x (IA + IM)

MGND = GND + Z1 x (ID + IA + IM) + Z2 x (IA + IM) + Z3 x IM
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Design guidelines
The STCOMET development kit has been designed with respect of a GND star connection,
especially between the digital and analog section as shown in Figure 30.
The PSU GND “(3)” is split between the AGND (green) and DGND (blue), at the position
“(1)”.
The MGND (green area bottom right) is connected to the AGND at the position “(2)”. Due to
distance between the MGND area and PSU GND, it was not possible to realize a full star
connection, unless having a long dedicated track that would increase the PCB size.
Figure 30. GNDs connections on STCOMET development kit board
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Design guidelines
10.1.4
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Power supply connections
Best practice rules must be applied to connection of STCOMET power supplies 3.3 V, 5 V
and VCC.
Decoupling capacitors must be placed as close as possible to their dedicated pins, the
smallest capacitor value being placed first. The associated capacitors/pins can be easily
identified on the schematic thanks to dedicated wires: for instance, the C29 and C30 are
dedicated to the pin 39, the C58 to the pin 83 and so on.
Wide tracks must be used for power supplies as much as possible. 2 mm wide tracks have
been used to carry VCC, 5 V and 3.3 V from PSU input (J13) to ferrite beads L3, L4 and L5.
Then, power has been deployed to the STCOMET using planes filling, as illustrated in
Figure 31.
Figure 31. Power supply distribution via tracks and copper planes
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10.1.5
Design guidelines
Mains voltage routing
The STCOMET development kit is connected to mains and as a consequence, special care
has been taken when routing the high voltage signals (line and neutral) on the board.
Especially, a minimum isolation distance has been applied on the PCB between tracks
connected to mains, considering both creepage and clearance.
Figure 32. Creepage and clearance isolation
The following extracts from schematics highlight the signals impacted by the isolation.
Figure 33. Tracks subject to specific isolation (1)
Figure 34. Tracks subject to specific isolation (2)
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There are several industry and safety standards that describe different spacing
requirements based on the voltage, application and other parameters.
The trace isolation on the STCOMET development kit has been set to 3.5 mm. This isolation
corresponds (with 0.3 mm additional margin) to the UL 60950-1 standard, with the specific
input data:

RMS working voltage = 250 V

Pollution degree = 3

Material group = I
Please notice also that, in case high voltage tracks would be placed on the PCB edge and
on the opposite layer, taking into account the creepage illustration in Figure 32, and
considering a PCB thickness = 1.6 mm, as a consequence the minimal distance between
the tracks and the PCB edge must be [3.5 mm - 1.6 mm]  2 = 0.95 mm.
10.1.6
Metrology connections
Voltage measurement connection
The STCOMET METR_VP and METR_VN inputs are dedicated to the mains voltage
measurement, through a resistor divider composed by R36 - R38 - R40 - R44. Dedicated
tracks have be designed from the line (L) to METR_VN and from neutral (N) to the R36 for
an accurate voltage measurement.
Particularly, the METR_VN input must not be tied directly to the GND ground plane at the
pin level, as shown in Figure 35:
Figure 35. GND connection for metrology voltage measurement
The mains voltage measurement is done between N and L (= GND). We can easily
understand in Figure 35 that if the METR_VN pin is directly tied to the GND plane (right
configuration), the voltage VN present at COMET inputs will be shifted by Z x (Isystem + IN)
compared to the real mains voltage, and this will introduce an error in the measurement.
This error cannot be compensated by metrology calibration since Isystem is not constant but
depends on the STCOMET activity (e.g.: PLC transmission). However, if a dedicated track
is used from the GND entrance to the METR_VN (left configuration), the error will be
minimized due to low value of IN and compensated by calibration.
The same recommendation can be applied to the neutral connection: use a dedicated track
going from the J37 to R36.
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Design guidelines
The application of those recommendations on the STCOMET development kit is illustrated
in Figure 36 by the blue and yellow arrows.
Figure 36. Dedicated tracks for voltage measurement
10.2
Oscillator section
The STCOMET requires two quartz crystals connected to the internal oscillators:

A 24 MHz oscillator for the main system clock and a quad frequency synthesizer (QFS)

A 32.768 kHz oscillator for the real-time clock (RTC) function.
It is very important to keep the crystal oscillators as close as possible to the STCOMET
device.
The resonant circuits must be far away from noise sources such as:

Power supply switching circuitry

Burst and surge protections

Line coupling circuits

Any PCB track or via carrying an RF switching signal
To properly shield and separate the oscillator section from the rest of the board, it is
recommended to use a ground plane, on both sides of the PCB, filling all the area below the
crystal oscillator. No tracks or vias, except for the crystal connections, should cross the
ground plane.
Connecting the case to ground could be a good practice to reduce the effect of radiated
signals on the oscillator.
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The load capacitors C87 - C88 have been selected in order to center the 24 MHz oscillator,
taking into account the additional capacitive load by the STCOMET pins and PCB. Those
values may have to be changed for any design using a different PCB layout and crystal.
There is no need to place external load capacitors for the 32.768 kHz oscillator since there
are integrated adjustable capacitors in the STCOMET at pins 100 and 101.
10.3
Power supply
The power supply circuit design is not only relevant in terms of available power. Two points
are particularly sensitive for a power line communication application:

The noise injected on the line

The input impedance of the power supply unit
Both points involve the EMI input filter design. The circuit of Figure 37 has been designed to
have minimum influence on the STCOMET line coupling circuit, in terms of load impedance
and linearity.
Figure 37. EMI input filter for the VIPER26H power supply module
L2
470uH
2
2
1
BR
DBLS208GRD
15mH 250V (Wurth 744821110 )
NTC 1
+ C3
33uF
t
F1
16
220nF-X 1
2A
3
2
1
F
1
CM
16
1mH
Wu rh TBD
2
4
1
C2
220nF
3
N
L1
4
NTC 2
t
C1
+
C4
33uF
AM039706
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11
FAQ and troubleshooting
FAQ and troubleshooting
In this section the most frequently asked questions and the solution to common STCOMET
development kit usage problems are described.
11.1
FAQ
Q: Is it possible to use the STCOMET on a medium or high voltage AC line?
A: Yes. A similar circuit solution as for the low voltage AC line can be used, provided that the
coupling interface (and particularly line transformer, power inductor and X1 capacitor)
guarantees adequate and safe isolation from the AC line.
Q: Is it possible to use the STCOMET on a DC or de-energized line?
A: Yes, the STCOMET can communicate over any wired connection, given that a suitable
coupling circuit is used to connect the device to the line.
Q: Why with the power line communication cannot get I 100% reachability even though the
range is few meters?
A: Probability lower than 100% to reach a PLC node within such a small distance can
depend on two main factors:

Attenuation or losses on the power line (for example because of some heavy capacitive
load connected close to the transmitter)

Noise coming from electric or electronic equipment connected on the power line (for
example SMPS, ballasts, motors).
It can be useful to measure the signal level at the transmitter and receiver to understand if
there are undesired losses. It is also important to measure the noise level and spectral
distribution to find whether the PLC channel is somehow “jammed” by noise.
Q: Will the power line communication work if a power distribution transformer is present
between two nodes?
A: The communication could work, but the transformer impedance at the signal frequency
must be taken into account, since it could introduce strong attenuation in the signal level.
A signal coupler (for example, a capacitive coupling) between the two sides of the
distribution transformers could be required.
Q: What method of the coupling is preferred for the medium voltage and low voltage mains
line: capacitive or inductive?
A: For the MV line, the capacitive coupling is preferable for the narrow-band PLC. In the
case of a LV line, being the actual line impedance unpredictable because of the number of
electrical devices connected on it, the solution should be an L-C series resonant circuit
tuned at channel frequency, designed to have low Q even with very low line impedance (5 
and below).
Q: Why to use zero crossing synchronization?
A: The zero crossing synchronization is not mandatory for the power line communication,
however it has several advantages.
For instance, it can improve the communication immunity against line noise, since most of
the electric equipment generate noise on the power line in correspondence of the mains
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voltage peak. Zero crossing synchronization allows establishing the link between the
transmitter and receiver during the time with the minimum time-dependent noise.
Zero crossing synchronization is also needed for three-phase communication. In case that
one node must communicate with nodes that are connected on other phases of the mains
network, zero crossing synchronization allows understanding in which phase a certain
message is coming from via delta-phase calculation.
Q: What could be the main sources of harmonic distortion in the STCOMET transmitted
signal?
A: Generally, harmonics can rise up because of
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
The high output current, due to low line impedance

Saturation of magnetic components in the line coupling circuit, due to either poor
dimensioning of the saturation current or to residual current at mains frequency

The capacitive load applied to the line driver output

The insufficient margin to the supply rails (low VCC or high output voltage).
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11.2
FAQ and troubleshooting
Troubleshooting
1.
PROBLEM: the STCOMET development kit doesn't work at all.
What to check:
2.
a)
Check that the AC mains supply cable is well connected.
b)
Check the voltage on VCC, +5 V, +3.3 V, 1.2 V. All those voltages must be present
for the STCOMET operation.
c)
Check the jumper and switch configuration according to the selected power supply
mode (Table 2 on page 16).
PROBLEM: the STCOMET development kit is not responding.
What to check:
3.
a)
Check if some activity is there when trying to communicate via the USB with the
board.
b)
Try disconnecting and reconnecting the USB cable; sometimes the USB driver
fails during the COM port opening or installing.
PROBLEM: the STCOMET development kit board does not transmit.
What to check:
4.
a)
Check the bias voltage on the line driver output (on J1 and J3) with the
oscilloscope probe referred to AGND. A DC voltage of VCC/2 must be measured.
b)
Check the presence of the output signal on the line driver, TX pre-driver and DAC
outputs while transmitting.
PROBLEM: the STCOMET development kit board transmits only for a short while; the
transmission is interrupted.
What to check:
5.
a)
Verify the temperature of the STCOMET.
b)
Check if there is the short-circuit (i.e.: capacitive) impedance on the mains at the
carrier frequency. It could lead to device overheating and the line driver thermal
shutdown.
PROBLEM: the STCOMET development kit board does not receive.
What to check:
Check if the transmitted signal reaches the STCOMET device by measuring the
RX_IN voltage (TP2 and TP3) by the oscilloscope probe referred to AGND.
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References
12
13
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References
1.
STCOMET datasheet
2.
STCOMET development kit schematics and PCB layout
3.
L2293Q datasheet
Normative references
EN50065: Signaling on low-voltage electrical installations in the frequency range 3 kHz to
148.5 kHz
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
Part 1: General requirements, frequency bands and electromagnetic disturbances

Part 2-3: Immunity requirements

Part 4-2: Low voltage decoupling filters - Safety requirements

Part 7: Equipment impedance
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14
Revision history
Revision history
Table 15. Document revision history
Date
Revision
01-Sep-2015
1
Initial release.
2
Updated Section : Introduction on page 1 (updated
whole Introduction, replaced STCOMET by
EVLKSTCOMET10-1, updated PLC protocols, added
description, updated title of Figure 1).
Minor modifications throughout document.
22-Oct-2015
Changes
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