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.