AN4068
Application note
ST7580 power line communication system-on-chip design guide
By Riccardo Fiorelli, Mauro Colombo
Introduction
The ST7580 reference design has been realized as a useful tool that exploits the
performance capability of the ST7580 power line networking system-on-chip.
With this reference design, it is possible to evaluate, directly on the power line, the
transmitting and receiving performance of a power line communication node based on the
ST7580 device.
The line coupling interface is designed to allow the ST7580 device to transmit and receive
on the AC mains line using the available FSK and PSK modes within the European
CENELEC EN50065-1 standard A band, specified for automatic meter reading (AMR)
applications [5]. The circuit has been designed to be easily adapted to different frequency
bands and application environments with very few modifications.
An STM32 microcontroller has been included in the reference design to make it more
flexible and suitable for use as a standalone smart PLC node.
Figure 1.
ST7580 reference design board with outline dimensions
As can be seen from the board image, special effort has been made to make the reference
design as compact as possible, while including all the features that enable the ST7580 to
perform at its best.
Note:
July 2012
The information provided in this application note refers to the EVALST7580-1 reference
design.
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www.st.com
Contents
AN4068
Contents
1
Abbreviations used in this document . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3
Safety recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4
ST7580 power line networking system-on-chip description . . . . . . . . 11
5
EVALKITST7580-1 evaluation tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6
Test and measurement tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7
ST7580 reference design description . . . . . . . . . . . . . . . . . . . . . . . . . . 14
7.1
7.2
8
9
7.1.1
Transmission active filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
7.1.2
Reception passive filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
7.1.3
Power line coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
7.1.4
Zero crossing coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
STM32 section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
7.2.1
Direct connections between STM32 microcontroller and ST7580 . . . . . 29
7.2.2
Digital interfaces to the STM32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
7.2.3
General purpose pushbuttons and LEDs . . . . . . . . . . . . . . . . . . . . . . . . 33
Reference design standard tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
8.1
Input impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
8.2
Conducted emission (CE) measurements . . . . . . . . . . . . . . . . . . . . . . . . 35
8.3
EMI immunity tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Design guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
9.1
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Line coupling section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
PCB layout guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
9.1.1
Thermal performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
9.1.2
Ground connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
9.2
Thermal impedance and power dissipation calculation . . . . . . . . . . . . . . 44
9.3
Oscillator section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
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Contents
9.4
10
11
Power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Application ideas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
10.1
3-phase architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
10.2
Received signal strength indication (RSSI) . . . . . . . . . . . . . . . . . . . . . . . 52
FAQs and troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
11.1
FAQs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
11.2
Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
12
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
13
Normative references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Appendix A Board layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
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List of tables
AN4068
List of tables
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6.
Table 7.
4/63
Electrical and thermal characteristics of the ST7580 reference design . . . . . . . . . . . . . . . . 8
TX_OUT level vs. TX_GAIN - typical values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Line coupling transformer specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Zero crossing coupling - measured timing characteristics . . . . . . . . . . . . . . . . . . . . . . . . . 28
Connections between STM32F103CBT6 and ST7580 devices on EVALST80-1 board . . 30
Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
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AN4068
List of figures
List of figures
Figure 1.
ST7580 reference design board with outline dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Figure 2.
ST7580 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Figure 3.
Board drawing with the various sections indicated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Figure 4.
Schematics of the ST7580 reference design board (part 1) . . . . . . . . . . . . . . . . . . . . . . . . 15
Figure 5.
Schematics of the ST7580 reference design board (part 2) . . . . . . . . . . . . . . . . . . . . . . . . 16
Figure 6.
Line coupling section schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Figure 7.
Measured frequency response of the transmission active filter (typical) . . . . . . . . . . . . . . 22
Figure 8.
Montecarlo simulation of the transmission active filter frequency response . . . . . . . . . . . . 22
Figure 9.
Measured frequency response of the reception passive filter (typical) . . . . . . . . . . . . . . . . 24
Figure 10. Montecarlo simulation of the reception passive filter response . . . . . . . . . . . . . . . . . . . . . 24
Figure 11. Measured frequency response of the transmission line coupling loaded with the EN50065-1
LISN impedance (typical)26
Figure 12. Measured frequency response of the transmission line coupling loaded with 5 W + 15 µF
(typical) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Figure 13. Montecarlo simulation of the transmission line coupling response loaded with the
EN50065-1 LISN impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Figure 14. Isolated zero crossing coupling circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Figure 15. Zero crossing coupling - positive edge delay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Figure 16. Zero crossing coupling - negative edge delay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Figure 17. Connections between the STM32F103CBT6 and the ST7580 devices on the
EVALST80-1 board. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Figure 18. STM32F103CB external connections: schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Figure 19. STM32 configurable signalling LEDs and pushbuttons . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Figure 20. Measured input impedance modulus of the line coupling - reception mode (typical) . . . . . 35
Figure 21. Measured input impedance modulus of the line coupling - transmission mode (typical) . . 35
Figure 22. Conducted emissions test setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Figure 23. Conducted emissions: PSK transmission spectrum, peak measurement, 9 kHz - 150 kHz,
line-to-earth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Figure 24. Conducted emissions: PSK transmission spectrum, peak measurement, 9 kHz - 150 kHz,
neutral-to-earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Figure 25. Conducted emissions: PSK transmission spectrum, quasi-peak measurement, 150 kHz 30 MHz, line-to-earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Figure 26. Conducted emissions: PSK transmission spectrum, quasi-peak measurement, 150 kHz 30 MHz, neutral-to-earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Figure 27. Conducted emissions: FSK transmission spectrum, peak measurement, 9 kHz - 150 kHz
, line-to-earth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Figure 28. Conducted emissions: FSK transmission spectrum, peak measurement, 9 kHz - 150 kHz,
neutral-to-earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Figure 29. Conducted emissions: FSK transmission spectrum, quasi-peak measurement, 150 kHz 30 MHz, line-to-earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Figure 30. Conducted emissions: FSK transmission spectrum, quasi-peak measurement, 150 kHz 30 MHz, neutral-to-earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Figure 31. Common mode disturbance protection - positive disturbance . . . . . . . . . . . . . . . . . . . . . . 41
Figure 32. Common mode disturbance protection - negative disturbance. . . . . . . . . . . . . . . . . . . . . . 42
Figure 33. Differential mode disturbance protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Figure 34. Example of stencil openings for the QFN48 package. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Figure 35. PCB copper dissipating area on top layer (left) and bottom layer (right) for the ST7580
reference design board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
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List of figures
Figure 36.
Figure 37.
Figure 38.
Figure 39.
Figure 40.
Figure 41.
Figure 42.
Figure 43.
Figure 44.
Figure 45.
Figure 46.
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Packet-fragmented transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Measured ST7580 thermal impedance curve (typical) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Simulation model of the thermal impedance ZthJA of the ST7580 mounted on the
reference design board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Example of power supply EMI input filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Scheme of principle for non-switched 3-phase architecture . . . . . . . . . . . . . . . . . . . . . . . . 49
Scheme of principle for switched 3-phase architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
3-phase isolated zero crossing coupling circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3-phase non-isolated zero crossing coupling circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
PCB layout - components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
PCB layout - top view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
PCB layout - bottom view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
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1
Abbreviations used in this document
Abbreviations used in this document
●
AC = alternate current
●
AFE = analog front end
●
AMR = automated meter reading
●
AWGN = additive white gaussian noise
●
BER = bit error rate
●
BOM = bill of material
●
CE = conducted emissions
●
DC = direct current
●
DL = data link layer
●
DSP = digital signal processor
●
EMC = electro-magnetic compliance
●
EMI = electro-magnetic interference
●
FSK = frequency shift keying
●
GUI = graphical user interface
●
NBI = narrow-band interferer
●
LISN = line impedance stabilization network
●
PA = power amplifier
●
PCB = printed circuit board
●
PHY = physical layer
●
PLC = power line communication
●
PSK = phase shift keying
●
PSU = power supply unit
●
RBW = resolution bandwidth
●
SBW = signal bandwidth
●
SNR = signal-to-noise ratio
●
SoC = system-on-chip.
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Electrical characteristics
2
AN4068
Electrical characteristics
Table 1.
Electrical and thermal characteristics of the ST7580 reference design
Value
Parameter
Notes
Min.
Typ.
Max.
Unit
Thermal data
Ambient operating temperature
-40
ST7580 thermal resistance
85
°C
50 (1)
°C/W
Measured on the ST7580 reference design
2-side PCB with thermal pad and 4x4
thermal via array
Transceiver section
Transmitting specifications (Tx mode)
20
Transmitted signal -20 dB
bandwidth
14.5
Transmitted output current limit
1
kHz
FSK 9600 baud
Any PSK mode
A rms
Receiving specifications (Rx mode)
B-PSK coded,
fC = 86 kHz, BER = 10-3
dBµ
Vrms
44
Minimum detectable received
signal
B-FSK, 9600 baud, fC = 86 kHz,
deviation=1, BER=10-3
58
Reception filter -3 dB bandwidth
65
kHz
Mains coupling specifications
Transformer isolation
4
(2)
kV
Power supply requirements
VCC power supply voltage
8
VCC power supply current
absorption – RX mode
VCC power supply current
absorption – TX mode
20
VDDIO digital supply voltage
-10%
VDDIO digital supply current
absorption
13
18
V
5
mA
JP7 closed (LK112SM33TR LDO not
enabled)
65
mA
JP7 open (LK112SM33TR LDO enabled)
500
mA
VCC = 8 to 18 V,
I(PA_OUT) = 0 to 1 A rms
+10%
V
3.3
60
mA
JP7 closed
No digital connection to external equipment
1. Measured over a continuous transmission period of 3000 seconds (steady-state thermal dissipation). See Figure 39 for
thermal impedance typical curve.
2. Note that ST does not guarantee transformer isolation. ST assumes no responsibility for the consequences that may arise
from such risks.
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Electrical characteristics
Table 2.
TX_OUT level vs. TX_GAIN - typical values
TX_OUT
TX_GAIN
[dBµV rms]
[V p-p]
FSK
PSK
31
3.900
123
120
30
3.450
122
119
29
3.100
121
118
28
2.750
120
117
27
2.450
119
116
26
2.200
118
115
25
1.950
117
114
24
1.750
116
113
23
1.550
115
112
22
1.380
114
111
21
1.225
113
110
20
1.100
112
109
19
0.975
111
108
18
0.870
110
107
17
0.775
109
106
16
0.690
108
105
15
0.615
107
104
14
0.550
106
103
13
0.490
105
102
12
0.435
104
101
11
0.390
103
100
10
0.345
102
99
9
0.310
101
98
8
0.275
100
97
7
0.245
99
96
6
0.220
98
95
5
0.195
97
94
4
0.175
96
93
3
0.155
95
92
2
0.140
94
91
1
0.125
93
90
0
0.110
92
89
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Safety recommendations
3
AN4068
Safety recommendations
The board must be used by expert technicians only. Due to the high voltage (85-265 Vac)
present on the non-isolated parts, special care must be taken in order to avoid the risk of
electric shock.
There is no protection against accidental contact with high-voltages.
After disconnection of the board from the mains, no live parts must be touched immediately
because of the energized capacitors.
It is mandatory to use a mains insulation transformer to perform any tests on the highvoltage sections, using test instruments such as, for instance, spectrum analyzers or
oscilloscopes.
Do not connect any probe to the high-voltage sections if the board is not isolated from the
mains supply, in order to avoid damage to instruments and demo tools.
ST assumes no responsibility for the consequences of any improper use of this
development tool.
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4
ST7580 power line networking system-on-chip description
ST7580 power line networking system-on-chip
description
The ST7580 is a flexible power line networking system-on-chip (SOC) combining a high
performing PHY DSP core and a protocol controller core with a fully integrated analog frontend (AFE) and line driver for a scalable future-proof, cost effective single-chip narrow-band
power line communication solution.
The device comes with embedded firmware providing a complete physical layer (PHY) and
some data link layer (DL) services for power line communication. The ST7580 protocol
services have been developed mainly for smart metering applications using CENELEC A
band, but they are also suitable for other command and control applications.
The embedded PHY layer, hosted in a DSP engine, implements two different modulation
schemes: a B-FSK modulation up to 9.6 kbps and a multi-mode PSK modulation with
channel quality estimation, dual channel receiving mode and convolutional coding,
delivering a throughput up to 28.8 kbps.
The embedded DL layer hosted in the embedded microcontroller offers framing and error
correction services.
Communication with an external microcontroller is based on a UART host interface,
exporting all the functions and services required to configure and control the device and its
protocol stack.
For further details, please refer to [1] and [2].
Figure 2.
ST7580 block diagram
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EVALKITST7580-1 evaluation tools
5
AN4068
EVALKITST7580-1 evaluation tools
The minimum set of evaluation tools to test the ST7580 power line communication requires
two communication nodes, each made up of the following elements:
●
a PC running the ST7580 GUI software tool
●
one EVALKITST7580-1 demonstration kit, composed of two boards:
–
EVALST7580-1 PLC board;
–
one EVLALTAIR900-M1 board as power supply unit (PSU).
For further details regarding the ST7580 GUI software and the available evaluation tools,
please visit http://www.st.com/powerline.
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6
Test and measurement tools
Test and measurement tools
●
Spectrum / network / impedance analyzer
–
●
Agilent 4395A: 10 Hz - 500 MHz
Agilent 43961A impedance test kit
–
Differential active probe
●
Agilent 1141A differential probe: 1 MΩ, 7 pF
●
Agilent 1142A probe control and power module: DC reject 0.05 Hz
●
EMC analyzer
●
–
Rohde&Schwarz ESL
–
9 kHz - 3 GHz
Two-line V-network (LISN)
–
●
Isolation transformer
–
●
1000 VA, 0 - 250 V variable output
Oscilloscope
–
●
Rohde&Schwarz ENV216
Tektronix DPO 7104C: 1 GHz, 20 GS/s
Surge/burst generator
–
Volta UCS 500-M.
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ST7580 reference design description
7
AN4068
ST7580 reference design description
The ST7580 reference design is made up of the following sections:
●
ST7580 device section
●
Line coupling section, including four subsections:
●
–
Transmission active filter
–
Reception passive filter
–
Power line coupling
–
Zero crossing coupling
STM32 microcontroller section.
The board has also six external connections:
–
AC mains (line and neutral) on CN1 connector;
–
VCC (8 to 18 V) and VDDIO (3.3 or 5 V) supply voltages on CN2 connector
–
SD storage card on CN3 micro SD connector
–
USB interface for PC connectivity on CN4 mini-USB connector
–
Digital interface on J2 (5x2 connector), collecting UART and I2C digital access to
the onboard STM32 microcontroller
–
JTAG interface for STM32 microcontroller on JTAG1 connector (10x2 connector).
Figure 3.
Board drawing with the various sections indicated
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Figure 4 gives a global view of the reference design.
Table 3 lists the components chosen to realize the reference design board. All the parts
have been selected in order to obtain good performance in a real case application.
The layout of the printed circuit board is reported in Figure 44, 45, and 46.
14/63
Doc ID 022923 Rev 2
Doc ID 022923 Rev 2
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AN4068
ST7580 reference design description
Schematics of the ST7580 reference design board (part 1)
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15/63
VDDIO
VDDIO
NC
R28
TCK
TXD
VDDIO
R30
R23
VDD
1
100k
TXD
RXD
VDDIO
TRSTN
TMS
GND
TCK
TDO
TDI
RESETN
VDD
XIN
8MHZ_MCO
1
100nF/25V
C34
100nF/25V
C36
R27
SHIELD
2
Doc ID 022923 Rev 2
100pF/C0G
C29
100nF/25V
C30
1
Q1
2N7002
R13
330R
CL_SEL
R18
10k
VDDIO
3k9
R14
CL_ADC
C47
10pF
100nF/25V
C11
100pF/C0G
R11
130R
JP11
CLOSE
VDDIO
VDDIO
10k
R44
3
SWA
SWB
CD
COM
C37
100nF
VBAT
PC13/TAMP/RTC
PC14
PC15
PD0/OSC-IN
PD1/OSC-OUT
NRST
STM32F103CBT6
VSSA
VDDA
PA0-WKUP
PA1
PA2
C39
4.7uF/10V (TANT)
16
15
14
13
12
11
10
9
VDDIO
1
2
3
4
5
6
7
8
SW4
PUSH_1
U3
EMIF06-MSD02N16
C46
10pF
RDATA_VCC
WP/CD
VCC
RDAT3_GND
DAT2_EX
DAT2_IN
DAT3_EX
DAT3_IN
CMD_EX
CMD_IN
CLK_EX
CLK_IN
DAT0_EX
DAT0_IN
DAT1_EX
DAT1_IN
PA_ADC
STM32_SD_NSS
STM32_SD_SCLK
STM32_SD_MISO
STM32_SD_MOSI
SD_CD
TP9
PA_ADC
VDDIO
uSD_NSS
uSD_MOSI
uSD_SCLK
uSD_MISO
JP10
CLOSE
JP8
CLOSE
PLC_RXD
330R
VDDIO
1
2
3
4
5
6
7
8
9
10
11
12
U4
VBUS
10K
SW3
PUSH_2
10K
R36
C41
10uF/6.3V
VDDIO
8MHZ_MCO
VDDIO
VDDIO
SPI2_MOSI
SPI2_MISO
SPI2_SCLK
SPI2_NSS
STM32_USB+
STM32_USBUART1_RXD
UART1_TXD
C44
4
5
CN4
CN-USB
JTAG_20P
JTAG1
2
4
6
8
10
12
14
16
18
20
J2
VDDIO
2
4 UART1_TXD
6 UART1_RXD
8
10
BLM21PG600SN1D
FB3
1
2
3
4
5
1
3
5
7
9
11
13
15
17
19
VDDIO
1
2
3
4
5
6
J1
STM32 SECTION
JP9
STM32 BOOT CONFIG
BOOT1
BOOT0
VDDIO
SW1
DIPSW-4P-90
SPI2 CONNECTOR
SPI2_MOSI
SPI2_MISO
SPI2_SCLK
SPI2_NSS
VDDIO
I2C1 - UART1 CONNECTOR
VDDIO
1
3
5
7
I2C1_SDA
9
I2C1_SCL
100nF/25V
I/O2#4
6
STM32_USB_PWR
I/O1#6
USBLC6-2P6
I/O2#3
GND
I/O1#1
U5
R34
STM32_SD_NSS
STM32_SD_MOSI
STM32_SD_SCLK
STM32_SD_MISO
SD_CD
SH2 SH2
SH1 SH1
BOOT1
C40
100nF/25V
VDD2
VSS2
PA13
PA12
PA11
PA10
PA9
PA8
PB15
PB14
PB13
PB12
36
35
34
33
32
31
30
29
28
27
26
25
1K5
BOOT0
R43
3
2
VDDIO
22R
22R
2
CN3
uSDCARD-HRS-DM3DSF
PLC_T_REQ
PLC_TXD
VDDIO
1
LED-RED
1
LED-Y ELLOW
1
LED-GREEN
R42
R46
1
J_TDO
STM32_RESET#
J_TRSTN
J_TDI
J_TMS
J_TCK
4
2
1
2
3
4
5
6
7
8
VDDIO
R56
4K7 1%
Y1
8MHz
CL_ADC
C42
2
DL5
2
470R
DL4
2
470R
DL3
470R
100nF/25V
STM32_NRST
PL_RX_ON
PL_TX_ON
20pF
C38
R45
R59
18K7 1%
SH2
SH1
DAT2/RSV
DAT3/CS
CMD/DATA_IN
VDD
SCLK
VSS2
DAT0/DATA_OUT
DAT1/RSV
SD_CD
R22
100k
VDDIO
PA_OUT
PLC_RESETN
SW5
STM32 RESET
VDDIO
20pF
C33
R35
R38
R40
STM32_USB+
STM32_USB-
1
C18
C27
100nF/25V
100nF/25V
C13
C8
10uF/25V
10K
10uF/6.3V
C12
CL
1
VCC
CL
PA_INPA_IN+
TX_OUT
RX_IN
ZC_IN
TP2
VCC
GND
R9
100nF/25V
C10
VDDIO
M25_Q
10uF/6.3V
C14
VCCA
VSS
C21
100nF/25V
VSSA
FB2
BLM21PG300SN1
VDD_REG_1V8
PA_OUT
M25_Q
CL_SEL
560R
VDDIO
560R
VDDIO
100nF/25V
C45
C28
10uF/10V
ST7580
U2
36
35
34
33
32
31
30
29
28
27
26
25
LED-RED
2
R32
DL2
1
PL_TX_ON
LED-GREEN
2
R31
DL1
PL_RX_ON 1
TP4
TREQ
CL_SEL
VSSA
VDDIO
GND
NC#32
RESERVED0
NC#30
NC#29
VDDIO
VDD_REG_1V8
PA_OUT
VSS
24
23
22
21
20
19
18
17
16
15
14
13
VDD_PLL
1
VCC
CL
PA_INPA_IN+
TX_OUT
RX_IN
ZC_IN
VCCA
VDD_PLL
VSSA
GND
XOUT
FB1
BLM21PG331SN1
R47
10K
2
24
23
22
21
20
19
18
17
16
15
14
13
ST7580 SECTION
TP8 TP7
TXD RXD
C32
100nF/25V
1
1
2
3
4
5
6
7
TCK
8
9
PLC_RESETN 10
11
12
TXD
RXD
PL_RX_ON
BR1
BR0
PL_TX_ON
I2C1_SCL
I2C1_SDA
MISO1
RN3
10K
VDDIO
SHIELD
SW2
ST7580 RESET
SH2
SH1
VDDIO
10K
10K
RN2
10K
VDDIO
100nF/25V
C35
EP
VDDIO
SCLK0
PL_RX_ON
T_REQ
BR1
BR0
PL_TX_ON
RESERVED1
RESERVED2
RESERVED3
GND
VDD
RESERVED4
RESERVED5
49
1
VDD1
VSS1
PB11
PB10
PB2
PB1
PB0
PA7
PA6
PA5
PA4
PA3
SHIELD
47K
I2C1_SCL
I2C1_SDA
MISO1
37
38
39
40
41
42
43
44
45
46
47
48
PA14
PA15
PB3
PB4
PB5
PB6
PB7
BOOT0
PB8
PB9
VSS3
VDD3
1
47K
T_REQ
BR1
BR0
C43
100nF/25V
8
7
6
5
I2C1_SCL
I2C1_SDA
37
38
39
40
41
42
43
44
45
46
47
48
R48
R49
R51
R50
1
2
3
4
8
7
6
5
J_TCK
J_TDI
J_TDO
J_TRSTN
10K
10K
10K
10K
1
2
3
4
J_TMS
47K
10K
R29
R25
R26
10K
10K
10K
10K
R24
R37
R33
4
3
2
1
16/63
10K
10K
10K
10K
R39
R41
GND
R55
R54
R53
R52
SH1
SH2
5
6
7
8
Figure 5.
SHIELD
VDDIO
ST7580 reference design description
AN4068
Schematics of the ST7580 reference design board (part 2)
3
1
2
EP
2
4.7uF/4V
C31
AM11115v1
AN4068
ST7580 reference design description
Table 3.
Bill of material
Reference
Value
Description
CN1
CON-MOLEX-KK100-3P
CON-MOLEX-42376-3P-90°
(pin 2 removed)
CN2
CON-MOLEX-KK100-3P
CON-MOLEX-42376-3P-90°
CN3
uSDCARD-HRS-DM3DSF
uSDCARD-HRS-DM3DSF
CN4
CN-USB
USBMB-HRS-UX60SC
C1_DC
NC
SMD-0805
C2
10 µF/50 V X5R
SMD-1206
C3
18 nF/25 V
SMD-0603
C4
220 nF X1
MKP safety capacitor - p=15 mm
C5
NC
MKP safety capacitor - p=22.5 mm
C6
10 nF/25 V
SMD-0603
C7,C10,C11,C13,C19,
C24,C26,C27,C30,C32,
C34,C35,C36,C40,C42,
C43,C45
100 nF/25 V
SMD-0402
C8
10 µF/25 V
SMD-1210
C9
4.7 pF/C0G
SMD-0402
C12,C14,C17,C41
10 µF/6.3 V
SMD-0603
C15,C18,C23,C29
100 pF/C0G
SMD-0402
C16
27 pF/C0G
SMD-0402
C20
100 nF/C0G
SMD-0402
C21,C44
100 nF/25 V
SMD-0603
C22
1 nF/C0G
SMD-0402
C25, C37
100 nF
SMD-0603
C28
10 µF/10 V
SMD-0805
C31
4.7 µF/4 V
SMD-0402
C33,C38
20 pF
SMD-0402
C39
4.7 µF/10 V (Tantalum)
SMD-3216
C46, C47
10 pF
SMD-0402
DL1,DL3
LED-green
SMD-0603
DL2,DL5
LED-red
SMD-0603
DL4
LED-yellow
D1
D2,D3
D4
SM6T15CA
(1)
STPS1L30A(1)
SM6T6V8CA
(1)
Doc ID 022923 Rev 2
SMD-0603
SMB
DO214AC
SMB
17/63
ST7580 reference design description
Table 3.
AN4068
Bill of material (continued)
Reference
Value
Description
D5
LL4148
SOD80
FB1
BLM21PG331SN1
Ferrite bead SMD-0805
FB2
BLM21PG300SN1
Ferrite bead SMD-0805
FB3
BLM21PG600SN1D
Ferrite bead SMD-0805
ISO1
TLP781(GB)
Photo-coupler DIP4
JP1,JP2
Open
Jumper SMD
JP3,JP4,JP10,JP11
Close
Jumper SMD
JP5
ST7580 UART
STRIP 5x1 2.54 mm male
JP6
STM32 PLC UART
STRIP 3x1 2.54 mm male
JP7,JP8
Close
Jumper 2x1 2.54 mm male
JP9
STM32 BOOT CONFIG
Jumper 2x2 2.54 mm male 90°
JTAG1
JTAG_20P
FLAT connector 10X2 male 90°
J1
SPI2 CONNECTOR
STRIP 6x1 2.54 mm male
J2
I2C1 – UART1 CONNECTOR
STRIP 5x2 2.54 mm male 90°
L1
15 µH
EPCOS B82464-A4153K
L2
220 µH
EPCOS B82462-A4224K
Q1
2N7002
SOT23
Q3
BC847C
SOT23
RN2,RN3
10 kΩ
RESN-CAY10
R1
NC
SMD-1206
R2
0Ω
SMD-1206
R3,R4,R7,R8
56 kΩ
SMD-2512
R5
150 Ω
SMD-0603
R6,R20
33 kΩ
SMD-0402
R9,R10,R23,R30,R34,
R36,R44,R47,R48,R49,
R50,R51
10 kΩ
SMD-0402
R11
130 Ω
SMD-0402
R12
22 kΩ
SMD-0402
R13
330 Ω
SMD-0402
R14
3.9 kΩ
SMD-0603
R15
5.1 kΩ
SMD-0402
R16
1.5 kΩ
SMD-0402
R17,R19
47 kΩ
SMD-0402
18/63
Doc ID 022923 Rev 2
AN4068
ST7580 reference design description
Table 3.
Bill of material (continued)
Reference
Value
Description
R18,R25,R33,R37,R39,
R41,
R52,R53,R54,R55
10 kΩ
SMD-0603
R21,R22
100 kΩ
SMD-0603
R24,R26,R29
47 kΩ
SMD-0603
R27
100 kΩ
SMD-0402
R28
NC
SMD-0402
R31,R32
560 Ω
SMD-0402
R35,R38,R40
470 Ω
SMD-0402
R42,R46
22 Ω
SMD-0402
R43
1.5 kΩ
SMD-0402
R45
330 Ω
SMD-0402
R56
4.7 kΩ 1%
SMD-0402
R57
1MEG
SMD-0402
R58
24 kΩ 1%
SMD-0402
R59
18.7 kΩ 1%
SMD-0402
R60, R62
22 kΩ
SMD-0402
SW1
DIPSW-4P-90
DIP switch 2.54 mm 4-way 90°
SW2
ST7580 RESET
Push button 90°
SW3
PUSH_2
Push button 90°
SW4
PUSH_1
Push button 90°
SW5
STM32 RESET
Push button 90°
TP1
PA_OUT
TP2
CL
TP3
RX_IN
TP4
T_REQ
TP5
TX_OUT
TP6
ZC_IN
TP7
RXD
TP8
TXD
TP9
PA_ADC
TP10
VSS
T1
TDK SRW13EP-X05H002
/ WE 750-510-231
PLC coupling transformer
U1
LK112SM33TR(1)
SOT23-5
U2
ST7580(1)
QFN48
Doc ID 022923 Rev 2
19/63
ST7580 reference design description
Table 3.
AN4068
Bill of material (continued)
Reference
Value
U3
Description
EMIF06-MSD02N16
(1)
MicroQFN 16L 3.5x1.2 mm
STM32F103CBT6(1)
U4
U5
USBLC6-2P6
Y1
LQFP48
(1)
SOT-666
8 MHz
XTAL-HC49U
1. ST parts on board.
7.1
Line coupling section
The line coupling section is made up of four different circuits: the transmission active filter,
the reception passive filter, the power line coupling, and the zero crossing coupling.
All four sections are described below. For each section, calculations and measured behavior
are reported.
The frequency response of the filters is usually sensitive to component value tolerance.
Actual components used in the ST7580 reference design have the following tolerances: +/20% for the X1 capacitor and the coils, +/- 5% for SMD ceramic capacitors, +/- 1% for SMD
resistors.
To evaluate sensitivity to these possible variations, simulated responses are also included,
with a Montecarlo statistical analysis of response variation vs. spread of component value.
For the transmission active filter, C0G/NPO type capacitors are required to guarantee
linearity and stability for any signal amplitude and frequency.
Figure 6.
Line coupling section schematics
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AN4068
7.1.1
ST7580 reference design description
Transmission active filter
The transmission active filter is based on the ST7580 internal power amplifier (PA), whose
input and output pins are externally available to allow a filtering network tailored around the
amplifier.
For the ST7580 reference design, a 3-pole low-pass filter has been realized by cascading a
simple R-C low-pass stage and a Sallen-Key 2-pole cell.
The R16-C22 low-pass stage has a corner frequency at nearly 110 kHz for a first filtering of
the TX_OUT harmonics. The 1 nF value of C22 has been found to be the optimal value to
obtain a good filtering action without yielding unwanted capacitive load distortion on the
TX_OUT line.
The transfer function of the 2nd order Sallen-Key cell is:
Equation 1
A( s ) =
A0
s
2
ωC
2
+
s
+1
ωC ⋅ Q
where:
Equation 2
A 0 = (1+
R6
) =4.3=12.7 db
R10
Equation 3
fC =
1
2π ⋅ R15 ⋅ R12 ⋅ C15 ⋅ C 23
=150 kHz
Equation 4
Q=
R15 ⋅ R12 ⋅ C15 ⋅ C 23
R12 C15 + R15 C23 + R15 C15 (1 − A 0 )
=1.03
Figure 7 represents the measured transfer function of the transmission active filter. It shows
good rejection at signal harmonic frequencies.
Doc ID 022923 Rev 2
21/63
ST7580 reference design description
Figure 7.
AN4068
Measured frequency response of the transmission active filter (typical)
A simulation of the transmission active filter response against component tolerance,
depicted in Figure 8, shows +/- 1 dB variation in gain module within the signal bandwidth,
while the Q variation is more sensitive around 100 kHz.
Figure 8.
22/63
Montecarlo simulation of the transmission active filter frequency
response
Doc ID 022923 Rev 2
AN4068
7.1.2
ST7580 reference design description
Reception passive filter
The reception filter is made up of the series of a resistor and a parallel L-C resonant. The
transfer function of the filter can be written as:
Equation 5
s ⋅ L 2 + RL
R5 L 2C3
R( s) =
s2 +
R5RL C 3 + L 2
R 5L 2 C 3
⋅s +
R 5 + RL
R 5L 2 C 3
where RL is the DC series resistance of the inductor (in this case, about 2 Ω).
The center frequency and the quality factor of the filter can be expressed as:
Equation 6
fc =
1
1 R5 + RL
1
⋅ ωC =
≅
=80 kHz
2π
2 π R 5L 2 C 3
2π L 2 C 3
Equation 7
Q=
R5 L 2 C3
R5R L C 3 + L 2
⋅ ωC =1.3
It is quite evident that the quality factor and the filter selectivity depend not only on the R5
value, but also on RL. Higher RL leads to lower steepness of the resonance, while higher R5
gives higher selectivity.
The RL value impacts insertion losses in a more evident way. To evaluate the relationship
between RL and the received signal loss, the following simplified expression of R ( s ) at f=fc
can be used:
Equation 8
R( j ⋅ 2 πfC ) ≅ Q ⋅
ωC ⋅ L 2
R5
=
1
1 + RL ⋅ R 5 ⋅
C3
L2
With actual values of the components, there is a loss of about 1 dB. The same calculation
gives unitary transfer if RL is set to zero.
Looking at the first way to express the module of the transfer function, it can be seen that a
higher Q can help to keep the losses small. However, a high Q would bring the response to
a higher sensitivity of the components' tolerance.
Figure 9 shows the measured frequency response of the Rx passive filter. The filter shows a
-3 dB bandwidth equal to 65 kHz and an attenuation of less than 1 dB at fC.
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ST7580 reference design description
Figure 9.
AN4068
Measured frequency response of the reception passive filter (typical)
Figure 10 represents a simulation of the response of the Rx passive filter with component
tolerance effect. The shift on center frequency gives a worst-case loss of nearly 0.5 dB at
center frequency.
Figure 10. Montecarlo simulation of the reception passive filter response
7.1.3
Power line coupling
The coupling to the power line requires some passive components in addition to the active
filtering stage. In particular, it includes the DC decoupling capacitor C2, the line transformer
T1, the power inductor L1, and the X1 safety capacitor C4.
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AN4068
ST7580 reference design description
L1 has been accurately chosen to have high saturation current (>2 A) and very low
equivalent series resistance (<0.1 Ω), to limit distortion and insertion losses even with heavy
line load.
Center frequency for the series resonance can be calculated at first approximation as:
Equation 9
fc =
1
=85 kHz
2 π L'1 ⋅ C4
′
provided that the capacitance of C2 is much greater than the C4 capacitance. L 1 is the
series of 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 C4 values, however, leads to limited attenuation due to either parasitic impedance or
resonance selectivity. If loaded with 5 Ω line impedance, the coupling circuit shows a Q
factor equal to 2 and a -3 dB bandwidth of 40 kHz (typical values).
Particular attention has been paid to the choice of 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 1 mH or greater, a leakage inductance much smaller than L1 and a total DC
resistance lower than 0.5 Ω.
The 4 kV insulation voltage requirement, the last specified parameter, is described and
codified by the EN50065-4-2 CENELEC document [2].
Table 4.
Line coupling transformer specifications
Parameter
Value
Turn ratio
1:1
Shunt inductance
≥ 1 mH
Leakage Inductance
≤1.5 µH
DC total resistance
≤0.5 Ω
DC saturation current
≥ 15 mA
Inter-winding capacitance
≤30 pF
Withstanding voltage
≥ 4 kV
In Figure 11 the measured response of the whole transmission coupling, loaded with the
LISN impedance as set by the EN50065-1 document, is reported. The image highlights a
further filtering effect added by the passive L-C series resonant combined with the LISN
reactive load.
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ST7580 reference design description
AN4068
Figure 11. Measured frequency response of the transmission line coupling loaded
with the EN50065-1 LISN impedance (typical)
Figure 12 shows the coupling response with 5 Ω + 15 µF line impedance.
Figure 12. Measured frequency response of the transmission line coupling loaded
with 5 Ω + 15 µF (typical)
Figure 13 represents the Montecarlo simulation of the cumulated response of transmission
active and passive filters, loaded with the LISN impedance as set by the EN50065-1
document. Due to the response slope and the effect of power components, the in-band
variation is within +/- 1.5 dB.
26/63
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AN4068
ST7580 reference design description
Figure 13. Montecarlo simulation of the transmission line coupling response loaded
with the EN50065-1 LISN impedance
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 VSS and
limited to ± 5 V peak [1].
The isolated zero crossing circuit is realized through an optocoupler in an inverting
configuration. Neutral and phase lines are brought to the optocoupler through four 56 kΩ, 1
W size SMD resistors in series, as represented in Figure 14. The LL4148 acts as a freewheeling diode during negative half-wave. The series resistors limit the photodiode input
current to nearly 1 mA rms at 230 VAC, leading to less than 250 mW of total consumption of
the solution. Having two resistors per line helps to prevent short-circuits in the case of
resistor degradation.
Figure 14. Isolated zero crossing coupling circuit
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ST7580 reference design description
AN4068
The timing characteristics of this circuit, according to the oscilloscope screenshots reported
below, are listed in Table 5.
Table 5.
Zero crossing coupling - measured timing characteristics
Edge
ZC delay
Positive
-75 +/- 300 µs
Negative
430 +/- 300 µs
Figure 15. Zero crossing coupling - positive edge delay
Figure 16. Zero crossing coupling - negative edge delay
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AN4068
7.2
ST7580 reference design description
STM32 section
The EVALST7580-1 is equipped with an STM32F103CBT6 device, a medium-density ARMbased 32-bit microcontroller.
For complete information on device characteristics, please refer to [3] and [4].
On the EVALST7580-1 board, the STM32F103CBT6 microcontroller can be used for the
following purposes:
●
to handle the ST7580 device through direct connections
●
for external access through several interface types: USB, SPI, I2C, USART, JTAG
●
to store and read data to/from an external µ-SD card
●
to develop test functions.
On the EVALST580-1, the STM32 microcontroller shares its VDD supply voltage with the
VDDIO digital supply of the ST7580 device.
A dedicated 8 MHz crystal has been provided with two suitable load capacitors according to
recommendations in [4].
7.2.1
Direct connections between STM32 microcontroller and ST7580
The STM32F103 microcontroller provides connections to the ST7580 for both digital and
analog parts.
Figure 17 is an extract of the EVALST7580-1 board and it highlights the connections
between the two devices only:
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ST7580 reference design description
AN4068
Figure 17. Connections between the STM32F103CBT6 and the ST7580 devices on the
EVALST80-1 board
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These connections involve several pins and features of the ST7580 modem, as listed in
Table 6.
Table 6.
Connections between STM32F103CBT6 and ST7580 devices on EVALST80-1 board
Connection
Host interface
type
Digital
ST7580 pins
STM32F103
pins
T_REQ
PA1
RXD
PA2
TXD
PA3
Notes
See [2]
Reset
Digital
RESETN
PC15
This direct connection allows the STM32
microcontroller to drive the RESETN pin
of the ST7580.
Clock
Digital
XIN
PA8
The connection must provide an 8-MHz
clock signal to the ST7580 modem in
accordance with the specifications in [1].
PL_RX_ON
PC13
PL_TX_ON
PC14
Power line
communication
activity
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Connection
Digital
Doc ID 022923 Rev 2
As the two lines give information about
power line communication activity of the
ST7580, the connections can be used as
input data for the STM32.
AN4068
Table 6.
ST7580 reference design description
Connections between STM32F103CBT6 and ST7580 devices on EVALST80-1 board
Connection
Connection
type
Transmitted
power line
signal levels
Analog
CL voltage level
7.2.2
Analog
ST7580 pins
STM32F103
PA_OUT
CL
Notes
pins
PB1
The connection allows the STM32 to
monitor the ST7580’s PA_OUT voltage
level. The connection is realized through a
suitable partition (between two high-value
1% tolerance resistors) to properly limit
the signal level within the STM32 input
range.
PA0
The connection allows the STM32 to
monitor ST7580’s CL pin voltage level and
to extract information about the ST7580
output current during power line
transmission.
Digital interfaces to the STM32
The EVALST7580-1 allows the STM32F103CB microcontroller to be accessed via its
available interfaces:
●
Serial wire/JTAG debug, that enables either a serial wire debug or a JTAG compliant
debug through the JTAG1 connector
●
USB 2.0 full speed through the mini-USB CN4 connector
●
2 SPI interfaces:
–
one is used to access an external µ-SD card with FAT32 support through the µ-SD
CN2 connector
–
the second works at 18 Mbit/s and presents the SPI signals at the J1 strip
connector
●
I2C
●
A second UART (TXD and RXD signals), in addition to the one used for the ST7580
connections.
I2C and UART signals are accessible through the same J2 double strip connector.
The NRST signal is externally accessible through a pushbutton.
An extract of the EVALST7580-1 board schematics for the digital interfaces of the STM32 is
depicted in Figure 18:
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AN4068
Figure 18. STM32F103CB external connections: schematics
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AN4068
7.2.3
ST7580 reference design description
General purpose pushbuttons and LEDs
The EVALST7580-1 board provides configurable input and output connections to the
STM32F103 microcontroller for both externally generated events and signaling purposes. In
fact, the board presents:
●
3 signaling LEDs, connected to PB5, PB6, PB7 outputs
●
2 pushbuttons connected to PB10, PB11, to manually generate events triggering
programmable functions.
Figure 19 is an extract of the schematics for these features.
Doc ID 022923 Rev 2
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!-V
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Reference design standard tests
AN4068
8
Reference design standard tests
8.1
Input impedance
The input impedance of a power line communication node is another critical point.
According to the network impedance measurements carried out in certain European
distribution networks (Italy, Germany and France), the following characteristics can be
associated to the impedance of a typical low-voltage (LV) power line:
●
Typical impedance magnitude is around 5 Ω
●
Nearly 90% of measured values range between 0.5 and 10 Ω
●
The impedance value depends on the measurement point
●
The measured value changes over time.
The reasons for these characteristics can be described as follows:
●
The LV distribution network has a “tree” structure, with many branches and subbranches acting as parallel impedances
●
Several electronic devices connected to the LV network offer a very low impedance,
mostly because of the EMI input filters installed at their mains connection
●
The type and number of electronic loads connected to the mains network varies over
time.
For all these reasons, particular attention must be paid to the impedance of the ST7580 line
coupling circuit. Specifically:
●
In receiving (idle) mode, the coupling impedance must be high enough to make the
power line source impedance negligible and to minimize the mutual interference
between different PLC nodes connected to the same network
●
In transmitting mode, the coupling impedance must be very low inside the signal
bandwidth but high enough for out-of-band frequencies.
According to such requirements, the EN50065-7 standard document fixes the following
constraints for the PLC node operating in the A band [5]:
●
●
Tx mode:
–
free in the range 3 to 95 kHz
–
3 Ω from 95 to 148.5 kHz
Rx mode:
–
10 Ω from 3 to 9 kHz
–
50 Ω between 9 and 95 kHz only inside the signal bandwidth (free for frequencies
outside the signal bandwidth)
–
5 Ω from 95 to 148.5 kHz.
Figure 20 and 21 show the input impedance magnitude vs. frequency measured in
transmission and reception mode.
The impedance magnitude values prove that the ST7580 reference design is compliant with
the EN50065-7 requirements. At the same time, the line interface gives an efficient signal
coupling both in transmission and reception.
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Reference design standard tests
Figure 20. Measured input impedance modulus of the line coupling - reception
mode (typical)
Figure 21. Measured input impedance modulus of the line coupling - transmission
mode (typical)
8.2
Conducted emission (CE) measurements
The EN50065-1 standard describes the test setup and the procedures for these kinds
of tests [5].
The compliance tests have been performed with a 230 VAC isolated supply. Different test
conditions have been set for PSK and FSK:
●
PSK: The test pattern consists of the continuous transmission of 200 ms packets with
50% duty cycle, random payload and B-PSK modulation with 86 kHz frequency. The
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Reference design standard tests
AN4068
output signal level has been set to nearly 9 V peak-to-peak (ST7580 TX_GAIN
parameter = 26), corresponding to 127 dBµV rms.
●
FSK: The test pattern consists of the continuous transmission of 200 ms packets with
50% duty cycle, random payload and FSK modulation with 82 kHz frequency at 9600
baud, deviation 1. The output signal level has been set to nearly 6 V peak-to-peak
(ST7580 TX_GAIN parameter = 21), corresponding to 126 dBµV rms.
Figure 22. Conducted emissions test setup
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The conducted emissions measurement results are reported below. Quasi-peak
measurements have been performed, as required by the EN50065-1 standard document,
for measurements above 150 kHz. Peak measurements are performed for frequencies
below 150 kHz to also show the output signal level compliance. The measured spectrum is
always compared to the EN50065-1 compliance limit mask.
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Reference design standard tests
Figure 23. Conducted emissions: PSK transmission spectrum, peak measurement,
9 kHz - 150 kHz, line-to-earth
Figure 24. Conducted emissions: PSK transmission spectrum, peak measurement,
9 kHz - 150 kHz, neutral-to-earth
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Reference design standard tests
AN4068
Figure 25. Conducted emissions: PSK transmission spectrum, quasi-peak
measurement, 150 kHz - 30 MHz, line-to-earth
Figure 26. Conducted emissions: PSK transmission spectrum, quasi-peak
measurement, 150 kHz - 30 MHz, neutral-to-earth
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Reference design standard tests
Figure 27. Conducted emissions: FSK transmission spectrum, peak measurement,
9 kHz - 150 kHz, line-to-earth
Figure 28. Conducted emissions: FSK transmission spectrum, peak measurement,
9 kHz - 150 kHz, neutral-to-earth
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Reference design standard tests
AN4068
Figure 29. Conducted emissions: FSK transmission spectrum, quasi-peak
measurement, 150 kHz - 30 MHz, line-to-earth
Figure 30. Conducted emissions: FSK transmission spectrum, quasi-peak
measurement, 150 kHz - 30 MHz, neutral-to-earth
8.3
EMI immunity tests
The specific structure of the coupling interface circuit of the application is a weak point
against high-voltage disturbances that can come from the external environment. In fact, an
efficient coupling circuit with low insertion losses realizes, consequently, a low impedance
path from the mains to the power line interface of the device.
For this reason it is recommended to add some specific protection on the mains coupling
path, to prevent high energy disturbances coming from the mains from damaging the
internal power circuitry of the ST7580.
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Reference design standard tests
Possible environments for this kind of application can be both indoor and outdoor:
residential, commercial and light-industrial locations. To verify the immunity of the system to
environmental electrical phenomena, a series of immunity specification standards and tests
must be applied to the power line application.
The immunity requirements for any PLC metering application, communicating in the
European A band (9-95 kHz), are listed in the EN50065-2-3 document, which refers to
EN61000 and ENV50204 for the tests to be applied [5].
These standards include surge tests, both common mode and differential mode (+/- 4 kV
peak, tR = 1.2 µs, tN = 50 µs) and fast transient (burst) tests (+/- 2 kV peak, tR = 5 ns, tH = 50
ns, repetition frequency 5 kHz).
For the application to be able to withstand such a severe electrical overstress, the line
coupling capacitor C4 must be an X1 or Y2 type part, rated for 4 kV or higher pulses.
In the case of non-metering applications, communicating outside the A band, the
requirements are listed in the EN50065-2-1 document, which sets lower pulse levels.
In addition to the line coupling capacitor, safety and robustness of the application are
guaranteed by protection devices included in the board design, such as input varistor (MOV)
and protection diodes. The effect of the protection diodes is described below.
Figure 31 and 32 show the protection against common mode disturbances. The low-drop
Schottky diodes D2 and D3 are able to quickly absorb fast transient disturbances exceeding
the supply rails.
Figure 31. Common mode disturbance protection - positive disturbance
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Reference design standard tests
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Figure 32. Common mode disturbance protection - negative disturbance
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Figure 33 describes the protection intervention in the case of differential mode disturbances.
A differential voltage higher than 15 V p-p is clamped by the D1 bi-directional Transil™
diode. D1 is the most robust protection and also the one that is able to absorb most of the
energy of any incoming disturbance.
Figure 33. Differential mode disturbance protection
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AN4068
Design guidelines
9
Design guidelines
9.1
PCB layout guidelines
9.1.1
Thermal performance
The ST7580 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 in order to keep it operating in
safe conditions.
Even though the ST7580 features a built-in thermal shutdown circuitry which turns off the
power amplifier (PA) when the die temperature (TJ) exceeds 150 °C, it is recommended not
to exceed 125 °C during normal operation to ensure the functionality of the IC.
A QFN48 package with exposed pad has been chosen for the ST7580 device in order to
obtain very good thermal performance. However, in order to take full advantage of this, the
PCB must be designed to effectively conduct heat away from the package.
To get a low impedance thermal path to the PCB, a 5x5 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. Therefore, the out-gassing phenomenon due
to the soldering process must be controlled to reduce solder voids between the QFN48
exposed pad and the PCB thermal pad. To achieve this, smaller multiple openings in the
solder paste stencil should be used instead of one big opening on the thermal pad region.
This also has the advantage of reducing the amount of solder paste used, therefore avoiding
bridges with perimeter pads.
A suitable example for the QFN48 package is shown in Figure 34.
Figure 34. Example of stencil openings for the QFN48 package
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Another technique to improve heat conduction on the top layer is to fill all unused areas with
copper tied to the dissipating ground plane.
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.
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An array of 4 x 4 thermal vias at 1.0 mm pitch, with a via diameter of 0.3 mm, has been
incorporated into the thermal pad, as shown in Figure 35.
To minimize the solder wicking effect due to open vias, possibly leading to poor soldering of
the QFN48 exposed pad, the via encroaching technique has been adopted (see bottom-side
image in Figure 35). The bottom-side solder resist has only 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.
Figure 35. PCB copper dissipating area on top layer (left) and bottom layer (right) for
the ST7580 reference design board
Another important parameter for effective heat dissipation is the copper thickness for both
top and bottom layers. 1 oz copper is considered as the minimum value to ensure good
dissipation.
The bottom-side routing plays an important role too. The solid ground area of copper under
the device must be as large as possible to minimize the thermal impedance. Therefore,
traces on the bottom side must run as far as possible from the device area.
9.1.2
Ground connections
Good soldering of the ST7580 exposed pad is required also to minimize ground noise.
Being the exposed pad connected to VSSA, its cleanliness is directly related to the noise
level detected by the receiving circuitry (i.e. to the actual sensitivity level) and to the PLL
behavior.
It is very important to filter each supply pin to its respective ground: VCC to VSS, VCCA and
VDD_PLL to VSSA, VDDIO and VDD to GND.
9.2
Thermal impedance and power dissipation calculation
The relationship between junction temperature (TJ) and power dissipation during
transmission (PD) is described by the following formula:
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Design guidelines
Equation 10
T J ( t TX , d) = TA + PD ⋅ Zth JA (t TX , d)
where TA is the ambient temperature (from -40 to +85 °C) and ZthJA is the junction to
ambient thermal impedance of the ST7580 IC, which is related to the length of the
transmission (tTX) and to the duty cycle d = tPKT / (tPKT + tIDLE), assuming a packetfragmented transmission as illustrated by Figure 36.
Figure 36. Packet-fragmented transmission
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When soldered to a proper dissipating area on the PCB as explained above, the ST7580 IC
is characterized by a steady-state thermal resistance RthJA of about 50 °C/W. The thermal
impedance curve obtained as the power dissipation step response is given in Figure 37.
Figure 37. Measured ST7580 thermal impedance curve (typical)
It can be seen that the transient of ZthJA takes some thousand seconds, after which the
static value of 50 °C/W is reached. This means that during the transient phase (i.e. if the
transmission time tTX is some seconds or even less) the IC is able to dissipate a power that
is far higher than the one sustainable at steady-state.
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For this reason, a complete thermal analysis requires that the characteristics of the
transmission, i.e. duty cycle and duration, are taken into account, determining the value
reached by the thermal impedance and then the allowed power dissipation.
The thermal impedance as a response to dissipation at different duty cycle and duration
values can be estimated by simulating a 6-cell equivalent model obtained through the curve
fitting from Figure 37, as shown in Figure 38.
Figure 38. Simulation model of the thermal impedance ZthJA of the ST7580 mounted
on the reference design board
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The actual dissipated power PD can be calculated as:
Equation 11
PD = PIN − POUT
where PIN = V CC ⋅ I CC and POUT = V OUTrms ⋅ I OUTrms. Note that power consumption by the
receiving circuitry and linear regulators is considered negligible for thermal analysis
purposes. The relationship between current absorption from the power supply (ICC) and PA
output current to the load (IOUT) is shown in Figure 2.
A transmission output level VOUT rms of 2.5 V, together with the current limit IOUT rms(LIMIT) of
1 A, corresponds to a maximum output power POUT of 2.5 W over a 1.5 Ω line load
(considering a 1 Ω coupling series impedance in transmission at 86 kHz frequency). In these
conditions, the required dissipation results as follows:
Equation 12
PD (LIMIT) = PIN(LIMIT) − POUT(LIMIT) ≅ (13V ⋅ 0.48A) − (2.5V ⋅ 1A) = 3. 7 W
Referring to the relationship between dissipated power and temperature, it can be proved
that in a continuous transmission, i.e. with ZthJA at its steady-state value of 50 °C/W, with an
ambient temperature of 25 °C, the maximum dissipation can be 2 W. However, by controlling
the transmission duty cycle and total duration it is possible to obtain a higher dissipation.
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Design guidelines
An example of communication with realistic values can be used in order to understand the
point:
●
9.3
B-PSK: considering 64 bytes of payload per message, the time to transmit one
message is nearly 65 ms. Transmitting five messages per second, the duty cycle is
32.5%; at this rate, sending 100 messages takes 20 seconds. According to the model
in Figure 38, in these conditions the ZthJA reaches 16.0 °C/W, allowing maximum
dissipation PD(LIMIT) with an ambient temperature up to 66 °C.
Oscillator section
The ST7580 internal oscillator circuitry requires a crystal having a maximum load
capacitance of 20 pF and a maximum ESR of 100 Ω. It is recommended to choose a quartz
crystal with overall tolerance not greater than 150 ppm to ensure stability of carrier
frequency and digital timing.
It is very important to keep the crystal oscillator and the load capacitors as close as possible
to the device.
The resonant circuit must be far away from noise sources such as:
●
Power supply circuitry
●
Burst and surge protection
●
Mains 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 may be good practice in order to reduce the effect of
radiated signals on the oscillator.
9.4
Power supply
The power supply requirements for the ST7580 reference design are listed in Table 1.
However, 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.
For the first point, a quasi-resonant switching mode power supply based on the ALTAIR04900 device has been chosen. This kind of switching controller spreads the switching
disturbances over a wide frequency range, therefore minimizing the overall disturbance
amplitude.
The second point involves the EMI input filter design. The suggested circuit in Figure 39 has
been designed to have minimum influence on the ST7580 line coupling circuit, in terms of
load impedance and linearity.
The 220 nF X2 capacitor has been put close to the bridge to avoid capacitive loading on the
ST7580 transmitted signal.
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Figure 39. Example of power supply EMI input filter
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Application ideas
10
Application ideas
10.1
3-phase architecture
The ST7580 modem can be used to communicate on a 3-phase network. This is especially
required for low-voltage substation nodes (concentrators), collecting data from several
energy meters all along the three phases of the distribution network.
In the example scheme of Figure 40, the line coupling circuit allows the signal to divide into
the three phases via capacitive coupling. That structure has been designed to keep similar
impedance on each phase, therefore optimizing the signal distribution between the phases.
A critical point regarding this solution may be the total impedance that the ST7580 power
amplifier is required to drive, which is the result of the three phases in parallel. For
concentrator nodes, however, the impedance per phase is likely to be considerably above
the driving limit of the power amplifier, as all the electrical devices supplied by the power line
are placed at a certain distance from the substation.
Figure 40. Scheme of principle for non-switched 3-phase architecture
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In the switched coupling scheme of Figure 41, a more complex circuit is shown, being the
coupling to each phase selectable via opto-switches.
Only one phase at a time can be used to transmit. The received signal, however, can be
picked up from either one phase at a time (J1 closed, J2 open) or any phase at the same
time (J1 open, J2 closed). Both solutions can work well: the first solution offers the
advantage of reducing crosstalk between the three phases, while the second allows the
whole network to be listened to at the same time. The choice depends on electrical and
performance tests as well as on specific protocol requirements.
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Figure 41. Scheme of principle for switched 3-phase architecture
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For the zero crossing coupling, even if only one phase at a time can be used as reference,
the possibility to switch to another phase is required in case of a fault on the reference line.
This can be achieved through one of the suggested circuits in Figure 42 and 43.
The external host must control the LCA715 opto-relays according to the phase status
information provided by the measurement circuitry. The host controller is also responsible
for ensuring that only one opto-relay is turned on, therefore guaranteeing isolation between
the three phases.
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Application ideas
Figure 42. 3-phase isolated zero crossing coupling circuit
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Figure 43. 3-phase non-isolated zero crossing coupling circuit
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Received signal strength indication (RSSI)
In many application fields, measuring the strength of the incoming signal is useful in
order to:
1.
Evaluate the SNR (signal to noise ratio) at the node
2.
Choose the best routing through the network (if repeaters are allowed).
As explained in [1] and [2], the ST7580 embeds estimators for SNR values. These
estimators are calculated during valid packet reception. The external host is notified of the
values during each data indication message [2].
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11
FAQs and troubleshooting
FAQs and troubleshooting
In this section the most frequently asked questions and solutions to common ST7580
reference design usage problems are described.
11.1
FAQs
●
Q: Is it possible to use ST power line transceivers on medium or high voltage AC lines?
–
●
Q: Is it possible to use the ST7580 on a DC or de-energized line?
–
●
A: Yes. In fact, the EN normative compliance intrinsically guarantees the
compliance with FCC part 15 regulations as well.
Q: What distance can be covered with a PLC signal?
–
●
A: The ST7580 device has been conceived as an open protocol device and can be
used according to the application needs. The user can develop their own protocol
or use a standard one.
Q: Does the ST7580 reference design meet FCC part 15 specs?
–
●
A: Yes. The ST7580 can communicate over any wired connection, given that a
suitable coupling circuit is used to connect the device to the line.
Q: Which kinds of protocols can be used with the ST7580?
–
●
A: Yes. The same circuit solution as for low-voltage AC lines can be used, provided
that the coupling interface (and particularly line transformer, power inductor and
the X1 capacitor) guarantees an adequate and safe isolation from the AC line.
A: Given a transmitted signal level of 2.5 V rms, in PSK mode the ST7580 device
is able to transmit through a channel attenuating up to 86 dB. This means that in a
point-to-point link, a distance of several km can be covered, according to the
characteristics of the line. Nevertheless, the allowable distance can be reduced
because of noisy devices and low-impedance loads connected on the power line;
such elements impact on the actual SNR seen by the receiver.
Q: Why, with power line communication, can I not get 100% reachability even though
the range is few meters?
–
A: A probability lower than 100% to reach a PLC node within such a small distance
can depend on two main factors:
a)
Attenuation or losses on the power line (for example because of some heavy
capacitive load connected close to the transmitter)
b)
Noise coming from electric or electronic equipment connected on the power line
(for example SMPS, ballasts, motors).
It may be useful to measure the signal level at transmitter and receiver to
understand if there are undesired losses. It is also important to measure the noise
level and spectral distribution to find out whether the PLC channel is somehow
“jammed” by noise.
●
Q: Does the power line communication work if a power distribution transformer is
present between two nodes?
–
A: The communication may work, but the transformer impedance at the signal
frequency must be taken into account, as it can introduce strong attenuation in the
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signal level. A signal coupler (for example, a capacitive coupling) between the two
sides of the distribution transformers may be required.
●
Q: What method of coupling is preferred for a medium-voltage and low-voltage mains
line: capacitive or inductive?
–
●
Q: Is it possible to detect the channel quality through the ST7580 device?
–
●
A: For an MV line, capacitive coupling is preferable for narrow-band PLC. In the
case of an LV line, having an unpredictable actual line impedance 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 Ω and below).
A: Yes. Using the ST7580 estimators for SNR, always available for the external
host, it is possible to evaluate the channel quality over the physical link between
transmitter and receiver.
Q: Why use zero crossing synchronization?
–
A: 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 electrical equipment generates noise on the power line in
correspondence with the mains voltage peak. Zero crossing synchronization
allows the establishing of the link between the transmitter and receiver during the
time with the minimum time-dependent noise.
Zero crossing synchronization is also needed for 3-phase communication. In a
case where one node must communicate with nodes that are connected on other
phases of the mains network, zero crossing synchronization understands which
phase a certain message is coming from via delta-phase calculation.
●
Q: What is the minimum signal-to-noise ratio that the ST7580 can manage?
–
●
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A: A bit error rate (BER) of 10-3 is used as reference. In this condition, the ST7580
can have good receiving performance with a signal-to-noise ratio down to 3-4 dB
for B-PSK coded mode.
Q: What could be the main sources of harmonic distortion in the ST7580 transmitted
signal?
–
A: Generally, harmonics can increase because of:
a)
High output current, due to low line impedance
b)
Saturation of magnetic components in the line coupling circuit, due to either poor
dimensioning of the saturation current or to 50 Hz residual current
c)
Capacitive load applied to the power amplifier output
d)
Insufficient margin to the supply rails (low VCC or high output voltage).
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11.2
FAQs and troubleshooting
Troubleshooting
1.
Problem: the ST7580 reference design board 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, VDDIO, VCCA, VDD, VDD_PLL lines. All these
voltages must be present to turn the ST7580 on.
c)
Verify if an 8-MHz clock is present on the XOUT pin (13) of the ST7580 device.
Problem: the ST7580 reference design board is not responding.
What to check:
3.
a)
Check if there is activity when trying to communicate via USB with the board.
b)
Try disconnecting and reconnecting the USB cable; sometimes the USB driver
fails during COM port opening.
c)
Try to reinstall the USB VCP driver for the STM32 on the PC.
d)
Try to reprogram the STM32 with the VCP driver FW.
Problem: the ST7580 reference design board does not transmit.
What to check:
4.
a)
Check the bias voltage on the PA_OUT test point (TP1) with the oscilloscope
probe referred to VSS power ground. A DC voltage of VCC/2 must be measured.
b)
Set the ST7580 in transmission via the ST7580 GUI. A modulated signal should
be detected by the oscilloscope probe, with amplitude equal to the TX_OUT
programmed level multiplied by the PA gain (see Section 7.1.1). If so, there is no
problem with the transmitter section of the ST7580.
Problem: the ST7580 reference design board transmits only for a short while; the
transmission is interrupted.
What to check:
5.
a)
Verify the internal temperature of the ST7580, available inside the management
information base (MIB) and accessible via the ST7580 GUI.
b)
Check if there is short-circuit (i.e. capacitive) impedance on the mains at the
carrier frequency. It may lead to device overheating and PA thermal shutdown.
Problem: the ST7580 reference design board does not receive.
What to check:
6.
Note:
a)
Check if the transmitted signal reaches the ST7580 device by measuring the
RX_IN line voltage (TP5) with the oscilloscope probe referred to VSSA signal
ground.
b)
Check that the GUI is setting the transmitter and the receiver to use the same tone
frequencies.
Problem: during a communication test, the ST7580 GUI shows high ‘bit error rate’
(BER).
This point refers to a half-duplex communication involving two ST7580 reference design
boards communicating with each other.
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What to check:
a)
Check that both reference design boards have the same ST7580 GUI settings.
b)
Verify the SNR of the communication. If the signal is too low or the noise is too
high with respect to each other, the communication performance is poor. Try to:
Check the SNR estimation of the receiving ST7580 device.
Measure the signal level S and the noise level N on the RX_IN line of the receiving
board.
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12
References
References
1.
ST7580 datasheet
2.
User manual UM0932
3.
STM32F103CB datasheet
4.
AN2867 application note
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Normative references
13
Normative references
5.
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EN50065: signaling on low-voltage electrical installations in the frequency range 3 kHz
to 148.5 kHz:
–
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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Board layout
Appendix A
Board layout
Figure 44. PCB layout - components
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Board layout
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Figure 45. PCB layout - top view
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Board layout
Figure 46. PCB layout - bottom view
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Revision history
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Revision history
Table 7.
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Document revision history
Date
Revision
Changes
27-Mar-2012
1
Initial release
04-Jul-2012
2
– Changed: Figure 4, 6, 14, 15 and 16
– Modified: Table 3 and 5
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