ST ST7540 Installation and operating instructions

January 2010 Doc ID 12791 Rev 3 1/55
AN2451
Application note
ST7540 FSK powerline transceiver
design guide for AMR
Introduction
The ST7540 reference design has been developed as a useful tool to demonstrate how a
small, high-performance powerline node can be built using the ST7540 FSK transceiver.
With this reference design, it is possible to evaluate the ST7540 features, in particular, its
transmitting and receiving performances through actual communication on the power line.
The ST7540 reference design may be considered to be composed of three main sections:
●Power supply section, specifically tailored to match powerline coupling requirements
and to operate within a wide range of the input mains voltage
●Modem and crystal oscillator section
●Line coupling interface section
The coupling interface is designed to allow the ST7540 FSK transceiver to transmit and
receive on the mains using 72 kHz carrier frequencies, within the European CENELEC
standard A-band specified for automatic meter reading.
Figure 1. ST7540 reference design board with outline dimensions
As it can be seen from the picture above, a special effort has been made to obtain a very
compact reference design board, while keeping the focus on transmission and receiving
performances.
Note: The information provided in this application note refers to EVALST7540-2 reference design
board.
52 mm
76 mm
www.st.com

Contents AN2451
2/55 Doc ID 12791 Rev 3
Contents
1 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2 Safety precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3 ST7540 FSK powerline transceiver description . . . . . . . . . . . . . . . . . . 10
4 Evaluation tools description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5 Board description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.1 Coupling interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.1.1 Tx active filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.1.2 Tx passive filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
5.1.3 Rx passive filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.1.4 Input impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.2 Conducted disturbances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
5.2.1 Conducted emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
5.2.2 Noise immunity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
5.3 Thermal design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.4 Oscillator section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.5 Surge and burst protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.6 50-pin connector for the EVALCOMMBOARD . . . . . . . . . . . . . . . . . . . . . 35
5.7 Power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
6 Performance and ping tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
7 Application ideas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
7.1 Three-phase architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
7.2 Zero crossing detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
7.3 Received Signal Strength Indicator (RSSI) . . . . . . . . . . . . . . . . . . . . . . . 44
7.4 Non-isolated coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
7.5 DC powerline applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
7.6 110 and 132.5 kHz coupling circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
8 Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

AN2451 Contents
Doc ID 12791 Rev 3 3/55
Appendix A Board layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
List of normative references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

List of figures AN2451
4/55 Doc ID 12791 Rev 3
List of figures
Figure 1. ST7540 reference design board with outline dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Figure 2. Typical curve for output current limit vs. RCL value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Figure 3. ST7540 Transceiver block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figure 4. Complete evaluation system including a PC, an EVALCOMMBOARD and the EVALST7540-
2 board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Figure 5. ST7540 powerline modem demonstration kit with control register window . . . . . . . . . . . . 12
Figure 6. Positioning of the various sections of the board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Figure 7. Modem and coupling interface schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Figure 8. Power supply schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Figure 9. Schematic of Rx and Tx filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Figure 10. Measured frequency response of the Tx active filter (typical curve). . . . . . . . . . . . . . . . . . 20
Figure 11. Simulated frequency response of the Tx active filter with components tolerance effect. . . 20
Figure 12. Measured frequency response of the Tx active + passive filters connected to the CISPR net-
work (typical curve) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Figure 13. Simulated frequency response of the Tx active + passive filters connected to the CISPR net-
work with the components tolerance effect22
Figure 14. Measured frequency response of the Rx passive filter (typical curve) . . . . . . . . . . . . . . . . 23
Figure 15. Simulated frequency response of the Rx passive filter with components tolerance effect . 24
Figure 16. Measured input impedance magnitude of coupling interface in Tx mode (typical curve) . . 25
Figure 17. Measured input impedance magnitude of coupling interface in Rx mode (typical curve). . 25
Figure 18. Conducted emissions test setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Figure 19. Output spectrum (typical) at 72 kHz, 2400 baud, deviation 1, mains 220Vac . . . . . . . . . . 26
Figure 20. Narrow-band conducted interference test setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Figure 21. Measured BER vs. SNR curve (typical), white noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Figure 22. SNR vs. frequency curve (typical) at BER = 10-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Figure 23. PCB copper dissipating area for ST7540 reference design board . . . . . . . . . . . . . . . . . . . 29
Figure 24. Packet-fragmented transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Figure 25. Equivalent model of the thermal impedance qJA of the HTSSOP28 package with exposed
pad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Figure 26. Output current vs. supply current typical curve for ST7540 in Tx mode . . . . . . . . . . . . . . . 31
Figure 27. Dissipated power vs. load impedance modulus typical curve for ST7540 reference design
board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Figure 28. A recommended oscillator section layout for noise shielding . . . . . . . . . . . . . . . . . . . . . . . 32
Figure 29. Common mode disturbances protection - positive disturbance . . . . . . . . . . . . . . . . . . . . . 33
Figure 30. Common mode disturbances protection - negative disturbance. . . . . . . . . . . . . . . . . . . . . 34
Figure 31. Differential mode disturbances protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Figure 32. Scheme of the connector for the EVALCOMMBOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Figure 33. Typical waveforms at 230 Vac: open load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Figure 34. Typical waveforms at 230 Vac: full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Figure 35. Typical waveforms at 265 Vac: short-circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Figure 36. Typical waveforms at 265 Vac: startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Figure 37. Load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Figure 38. SMPS efficiency curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Figure 39. ST7540 powerline modem demonstration kit window for the master board . . . . . . . . . . . . 41
Figure 40. Scheme of principle for three-phase architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Figure 41. Schematic of a zero crossing detection circuit for non-isolated coupling . . . . . . . . . . . . . . 43
Figure 42. Schematic of a zero crossing detection circuit for isolated coupling. . . . . . . . . . . . . . . . . . 44
Figure 43. ZC_OUT vs. AC mains waveforms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

AN2451 List of figures
Doc ID 12791 Rev 3 5/55
Figure 44. Peak detector electrical schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Figure 45. Measured DC_OUT Vs. AC_IN peak detector response . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Figure 46. Example schematic for non-isolated solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Figure 47. Line coupling interface for 110 kHz channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Figure 48. Line coupling interface for 132.5 kHz channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Figure 49. PCB layout - component placing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Figure 50. PCB layout - top view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Figure 51. PCB layout - bottom view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

List of tables AN2451
6/55 Doc ID 12791 Rev 3
List of tables
Table 1. Electrical characteristics of the ST7540 reference design . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Table 2. Output voltage level setting through Vsense partitioning - typical values . . . . . . . . . . . . . . . 8
Table 3. Bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Table 4. ST parts on the ST7540 reference design board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Table 5. Line coupling transformer specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Table 6. Noise immunity test settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Table 7. 50-pin connector digital signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Table 8. 50-pin connector analog signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Table 9. 50-pin connector power connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Table 10. SMPS specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Table 11. SMPS transformer specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Table 12. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

AN2451 Electrical characteristics
Doc ID 12791 Rev 3 7/55
1 Electrical characteristics
Table 1. Electrical characteristics of the ST7540 reference design
Parameter Test conditions
Value
Unit
Min Typ Max
Operating conditions
Ambient operating temperature
If ST7540 junction temperature
exceeds 180 °C device shuts
down
85 °C
Transceiver section transmitting specifications (Tx mode)
Selected channel frequency FSK carrier 72 kHz
Transmitting output voltage level at mains output R7 = 47kΩ, R8 = 15kΩ– See
Table 2 22.25Vrms
Transmitting output current limit R6=1.1kΩ– See Figure 2 500 mA rms
2nd harmonic distortion
at mains output
Loaded with CISPR 16-1
network -55
dBC
3rd harmonic distortion
at mains output
Loaded with CISPR 16-1
network -61
50Hz attenuation 100 dB
Receiving specifications (Rx mode)
Minimum detectable Rx signal BER<10-3, negligible noise 48 dBµV rms
Auxiliary supply
5 V regulated voltage ST7540 internally generated -5% 5.05 +5% V
5 V current capability 50 mA
3.3 V regulated voltage ST7540 internally generated -5% 3.3 +5% V
3.3 V current capability 50 mA
Power supply section
AC mains voltage range 85 265 V
Mains frequency 50-60 Hz
Output voltage Green led ON -10% 12.3 +10% V
Output voltage ripple Iout = 500 mA, Vin=85 Vac 1 %
Peak output current 500 mA
Output power 5.6 W
Efficiency at Pout=3.5W 70 %
Nominal transformer isolation* Primary to secondary/
secondary to auxiliary 4 kV

Electrical characteristics AN2451
8/55 Doc ID 12791 Rev 3
Figure 2. Typical curve for output current limit vs. RCL value
Number of holdup cycles 0
Input power 100 mW
Switching frequency Transceiver section in Tx mode -10% 65 +10% kHz
Switching frequency Transceiver section in Rx
mode -10% 21 +10% kHz
Table 1. Electrical characteristics of the ST7540 reference design (continued)
Parameter Test conditions
Value
Unit
Min Typ Max
Table 2. Output voltage level setting through Vsense partitioning - typical values
V(PA_OUT)
[VP-P]
V(PA_OUT)
[VRMS]
V(PA_OUT)
[dBuVRMS]
R7
[kΩ]
R8
[kΩ]
2.830 1.000 120 16 15
3.170 1.120 121 20 15
3.560 1.260 122 24 15
3.990 1.410 123 27 15
4.470 1.580 124 33 15
5.030 1.780 125 39 15
5.660 2.000 126 47 15
6.340 2.240 127 51 15
7.100 2.510 128 56 15
7.980 2.820 129 68 15

AN2451 Safety precautions
Doc ID 12791 Rev 3 9/55
2 Safety precautions
The board must be used only by expert technicians. Due to the high voltage (220 V ac)
present on the parts which are not isolated, special care should be taken with regard to
people's safety.
There is no protection against high voltage accidental human contact.
After disconnection of the board from the mains, none of the live parts should 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 (see circuit sections highlighted in Figure 7 and Figure 8) in which test
instruments like Spectrum Analyzers or Oscilloscopes are used.
Do not connect any oscilloscope probes to high voltage sections in order to avoid damaging
instruments and demonstration tools.
Warning: ST assumes no responsibility for any consequences which
may result from the improper use of this tool.

ST7540 FSK powerline transceiver description AN2451
10/55 Doc ID 12791 Rev 3
3 ST7540 FSK powerline transceiver description
ST7540 transceiver uses frequency shift keying (FSK) modulation to perform a half-duplex
communication on a powerline network. It operates from a 7.5 to 13.5 V single supply
voltage (Vcc) and integrates a power amplifier (PA), which is able to drive low line
impedance, and two linear regulators providing 5 V and 3.3 V.
Figure 3. ST7540 Transceiver block diagram
The ST7540 can communicate using eight different communication channels (60, 66, 72,
76, 82.05, 86, 110, 132.5 kHz), four baud rates (600, 1200, 2400, 4800) and two deviations
(1 and 0.5). Additional functions are included, such as watchdog, automatic control on PA
output voltage and current, carrier/preamble detection and band-in-use signaling,
transmission time-out, and thermal shutdown.
The transceiver, which is dedicated only to physical communication, operates with a
microcontroller whose aim is to manage the communication protocol stack. A reset output
(RSTO) and a programmable clock (MCLK) can be provided to the microcontroller by the
ST7540 in order to simplify the external logic and circuitry.
The host controller can exchange data with the transceiver through a serial interface,
programmable to operate either in UART (CLR/T data clock not used) or in SPI mode.
Communication on the power line can be either synchronous or asynchronous to the data
clock that is provided by the transceiver at the programmed baud rate.
When in transmission mode (i.e. RxTx line at low level), the ST7540 samples the digital
signal on the TxD line at the programmed baud rate and modulates it in a FSK sinusoidal
output on the Tx_OUT line. This signal is then externally fed into the power amplifier to add
current capability. The power amplifier can also introduce gain and active filtering to the
signal, just using few external passive components. The resulting signal on the PA_OUT line
is coupled to the power line.
When in receiving mode (i.e. RxTx line at high level), an incoming FSK signal on the Rx_IN
line is demodulated and the digital output is available for the microcontroller on the RxD pin.

AN2451 Evaluation tools description
Doc ID 12791 Rev 3 11/55
The device also recovers the synchronism of the received signal using an internal PLL. The
recovered clock is present on CLR/T output.
The ST7540 operating parameters can be set by means of an internal control register,
accessible only through the SPI host interface.
4 Evaluation tools description
The complete evaluation system for the ST7540 powerline communication consists of:
●a PC using the "ST7540 power line modem demo kit" software tool
●one EVALCOMMBOARD hosting the ST7 microcontroller
●one ST7540 reference design board (EVALST7540-2).
The correct procedure for connecting the EVALST7540-2 and the EVALCOMMBOARD is as
follows:
1. Connect the EVALST7540-2 and the EVALCOMMBOARD
2. Connect the ac mains cable to the EVALST7540-2 and the USB cable to the
EVALCOMMBOARD
3. Connect the EVALST7540-2 to the ac mains supply
4. Connect the EVALCOMMBOARD to the PC via the USB cable.
Warning: Follow the connection procedure to avoid damaging the
boards.
Figure 4. Complete evaluation system including a PC, an EVALCOMMBOARD and
the EVALST7540-2 board
U
US SB B/
RS232

Evaluation tools description AN2451
12/55 Doc ID 12791 Rev 3
Figure 5. ST7540 powerline modem demonstration kit with control register window
The complete chain, controlled by the ST7540 powerline modem demonstration kit, can set
up real communication at bit level, simply by sending or receiving a user-defined bit stream.
It is possible to establish a half-duplex communication with two of these communication
nodes (two chains) connected to each other. In order to better evaluate communication
between two nodes, the ST7540 powerline modem demonstration kit has some particular
features, including:
●Frame synchronization: a byte synchronization header can be added to the to the
exchanged data to set up a simple protocol, intended to test the capability of the
system to correctly receive the exact transmitted bit sequence. This can be done in two
ways: via the ST7540 control register settings (the internal configuration register of the
modem has a frame header field, in which an 8- or 16-bit header can be set) or via the
Rx panel of the ST7540 powerline modem demonstration kit (setting a synchronization
at SW level). A bit synchronization can be introduced as a simpler feature by enabling
the preamble detection method in the control register panel and then inserting at least
one “0101” or one “1010” sequence at the beginning of the transmitted bit stream.
●Ping session: a master-slave communication with automatic statistics calculation can
be very useful to test a point-to-point or a point-to-multipoint powerline communication
network, thus providing a method to evaluate reachability of each node in the network.
For further details about the ST7540 powerline modem demonstration kit, please refer
to the user manual UM0239 “ST7540 power line modem demo kit graphical user
interface”.

AN2451 Board description
Doc ID 12791 Rev 3 13/55
5 Board description
The ST7540 reference design is composed of the following sections:
●Power supply section, based on ST’s VIPer12A-E IC
●ST7540 modem and crystal oscillator section
●Line coupling interface section, with three subsections:
– Transmission active filter
– Transmission passive filter
– Receiving passive filter.
The board also has two connectors, which allow the user to plug the mains supply on one
side of it and the I.B.U. communication board on the other side.
Figure 6. Positioning of the various sections of the board
The schematics of the whole reference design appear in Figure 7 and 8. Figure 7 shows
the modem and the coupling Interface circuits, while Figure 8 represents the power supply
circuit. In both the schematics, high voltage regions are highlighted.
Tabl e 3 lists the components used to develop the reference design board. All parts have
been selected to give optimal performances.
The layout of the printed circuit is given in Appendix A - Figure 49, Figure 50 and Figure 51.

Board description AN2451
14/55 Doc ID 12791 Rev 3
Figure 7. Modem and coupling interface schematic

HIGH
VOLTAGE
SECTION

AN2451 Board description
Doc ID 12791 Rev 3 15/55
Figure 8. Power supply schematic
4 3
N
PVcc
Vcc
FB Vdd
DRAIN
S
AC INPUT
85 V ac to 256 V ac
DC OUTPUT
12 V dc
TEST PADS
C10 2.2 nF C10 2.2 nF
1 4 3 2
8 5
T1T1
1
23
Q1Q1
L1
1 mH
L1
1 mH
C6 10 uF C6 10 uF
C7 47 nF C7 47 nF
+
C8 470uF 16V
+
C8 470uF 16V
R2 220k R2 220k
R5 1k5 R5 1k5
R1
10R 1W
R1
10R 1W
L3 470uH L3 470uH
2 1
D4D4
R3 10 K R3 10 K
1 3
2
D5 10V D5 10V
+
C3 10uF 400V
+
C3 10uF 400V L4
33 uH L4 33 uH
1 24
3
U2U2
2 4 1 3 6
5 7 8
U1U1
4
1
3
2
-+
D1
BRIDGE
-+
D1
BRIDGE
+
C2
10uF 400V
+
C2
10uF 400V
13
D3D3
C4 470pF 630V C4 470pF 630V
D6 LED D6 LED
C5 220 pF C5 220 pF
1 2
CN1CN1
F1 T - 2A F1 T - 2A
D2D2
6 10
5 1
L2L2
C1
33nF X2
C1
33nF X2
C29
47uF 16V
C29
47uF 16V
VccVcc VssVss
R4 560 R4 560
C9
47uF 16V
C9
47uF 16V
HIGH
VOLTAGE
SECTION

Board description AN2451
16/55 Doc ID 12791 Rev 3
Table 3. Bill of materials
Item Qty Part Value Description
1 1 CN1 HEADER 2 Mains supply connector
2 1 CN2 CON50A 50 pins SMT right angle female p=1.27mm
3 1 C1 33nF X2 Murata GA355XR7-GB333K
4 2 C2,C3 10uF / 400V Yageo SE-K / Nichicon VK 20%
5 1 C4 470pF / 1kV TDK C4520X7R-3A471K
6 1 C5 220pF / 50V TDK C0603C0G-1E220J
7 4 C6,C15,C17,C24 10uF / 16V TDK C3216X7R-1C106MT
8 1 C7 47nF / 25V Murata GRM188R7-1E473K
9 1 C8 470uF / 16V Rubycon 3M0319 / Yageo SE-K 20%
10 2 C9,C29 47uF / 16V Murata GRM32ER6-1C476K
11 1 C10 2.2nF Y1 TDK CD12-E2GA222MYNS /
Murata DE1E3-KX222M
12 2 C11,C12 33pF TDK C1005C0G-1H330J
13 2 C14,C27 10nF Murata GRM188R7-1H103K
14 4 C16,C18,C19,C25 100nF TDK C1608X7R-1H104K
15 2 C21,C33 150pF Murata GRM1885C-1H151J
16 1 C22 10uF Murata GRM21BR6-1A106K /
TDK C2012X5R-0J106K
17 1 C23 100nF X2 EPCOS B32922-A2104K
18 1 C26 22nF Murata GRM21B5C-1H223J /
TDK C3216C0G1H223J
19 1 C30 15pF Murata GRM1555C-1H150J
20 1 C31 22pF Murata GRM1555C-1H220J
21 1 C32 390pF Murata GRM1885C-1H391J
22 1 D1 DF06S 600 V - 1.5 A bridge rectifier
23 1 D2 STTH1L06A SMA ultra-fast Schottky diode
24 1 D3 BAS16 / BAS21 SOT23
25 1 D4 STPS1H100 SMA Schottky diode
26 1 D5 BZX84C10 SOT23 10V zener diode
27 1 D6 LED Green LED
28 2 D8, D10 BAT54S SOT23 low drop Schottky diode
29 1 D9 SM6T12CA 12V bidirectional transil diode
30 1 F1 2A - T Time-lag fuse
31 1 JP4 CLOSE
32 1 J1 CONNECTOR

AN2451 Board description
Doc ID 12791 Rev 3 17/55
33 1 L1 1mH Epcos B82442-H1105K
34 1 L2 2x10mH 0.3A Radiohm 42V15
35 1 L3 470uH Epcos B82442-A1474K
36 1 L4 33uH Epcos B82462-A4333K
37 1 L5 47uH Epcos B82464-A4473K /
WE 744-775-147
38 1 L6 220uH Epcos B82462-A4224K /
WE 744-774-222
39 1 Q1 BC857BL SOT23
40 1 R1 10R 1W Metal oxide type - radial
41 1 R2 220K 0603 1%
42 1 R3 10K 0603 1%
43 1 R4 560 0603 1%
44 1 R5 1K5 0603 1%
45 1 R6 1K1 0603 1%
46 1 R7 47K 0603 1%
47 1 R8 15K 0603 1%
48 1 R9 4K7 0603 1%
49 1 R10 12K 0603 1%
50 1 R12 1K 0603 1%
51 1 R14 1K8 0603 1%
52 1 R17 470 0603 1%
53 1 R19 3K9 0603 1%
54 1 R20 56K 0603 1%
55 1 R21 2K7 0603 1%
56 1 T1 SMPS
transformer
TDK SRW12.6EF-E07H013 /
WE S06-100-057
57 1 T2 Line
transformer
VAC T60403-K5024-X044 /
Radiohm 69H14-2101
58 1 U1 VIPER12AS SMPS controller / switch
59 1 U2 SFH610-A Opto-switch
60 1 U3 ST7540 Powerline transceiver
61 1 X1 16 MHz
Table 3. Bill of materials (continued)
Item Qty Part Value Description

Board description AN2451
18/55 Doc ID 12791 Rev 3
5.1 Coupling interface
The mains coupling interface is composed of three different filters: the Tx active filter, the Tx
passive filter and the Rx passive filter.
All three filters are described in the sections Section 5.1.1, 5.1.2, and 5.1.3. In each section,
calculations and measured frequency responses are given.
The filters are quite sensitive to the components' value tolerance. Actual components used
in the ST7540 reference design have the following tolerances:
●+/- 10% for coils and for the X2 capacitor
●+/- 1% for SMD resistors
●+/- 5% for SMD ceramic capacitors.
To evaluate sensitivity of the filters to the tolerances listed above, the following sections
include simulated responses of the filters with Montecarlo statistical analysis. Statistical
simulation helps understanding the relationship between components' value tolerance and
variations on the responses of the filters. In simulation curves, the ideal response is drawn in
blue, while red curves indicate statistical variations generated through simulation.
Table 4. ST parts on the ST7540 reference design board
Value Description
ST7540 Powerline transceiver
VIPER12AS SMPS controller / switch
STTH1L06A Ultrafast diode
STPS1H100 Schottky diode
SM6T12CA 12V bidirectional transil diode

AN2451 Board description
Doc ID 12791 Rev 3 19/55
Figure 9. Schematic of Rx and Tx filters
5.1.1 Tx active filter
The Tx active filter is based on the ST7540 internal power amplifier (PA), whose input and
output pins are available externally to allow a filtering network to be tailored around the
amplifier.
For the ST7540 reference design board, a 3-pole low-pass filter has been developed by
cascading a simple R-C low-pass stage and a Sallen-Key 2-pole cell with 9dB gain. The
R19-C32 low-pass stage is aimed at introducing attenuation starting from approximately an
octave above the transmission channel frequency.
The transfer function of the 2nd order Sallen-Key cell is:
Equation 1
The corner frequency may be calculated as:
Equation 2
Figure 10 represents the measured transfer function of the Tx active filter. It shows good
rejection on both the 2nd and 3rd harmonic frequencies for the 72 kHz signal.
As() A0
s2
ωC
2
---------- s
ωCQ•
------------------1++
---------------------------------------------=
A01R14
R12
---------+
⎝⎠
⎛⎞
ωC
1
R9R10
•C33 •C21 •
---------------------------------------------------------=,=QR9R10
•C33 •C21 •
R9C33 R10C21 R9C21 1A
0
–()++
----------------------------------------------------------------------------------------=
where and
fc
1
2πR9R10
•C33 •C21 ••
---------------------------------------------------------------------- 135.7kHz==

Board description AN2451
20/55 Doc ID 12791 Rev 3
Figure 10. Measured frequency response of the Tx active filter (typical curve)
Simulation of the Tx active filter response against components' tolerance, depicted in
Figure 11, shows +/- 1 dB variation in gain module at 72 kHz.
Figure 11. Simulated frequency response of the Tx active filter with components
tolerance effect
5.1.2 Tx passive filter
Coupling to the power line requires some passive components in addition to the active
filtering stage. In particular, Tx passive filter section is made of the decoupling capacitor
C22, line transformer T2, inductor L5 and X2 safety capacitor C23.
L5 has been accurately chosen to have a high saturation current (>1 A) and a very low
equivalent series resistance (<0.2 Ω), to limit distortion and insertion losses even with heavy
line load. Center frequency for the series resonance is calculated as:
Equation 3

+/‐1dB
fc
1
2πL5C23
•
---------------------------------=