ST ST7538Q Installation and operating instructions

April 2008 Rev 1 1/56
56
AN2744
Application note
ST7538Q power line FSK transceiver
dual channel reference design for AMR
Introduction
The ST7538Q dual channel reference design is a practical tool to start the activity of
designing an automatic meter reading (AMR) node based on the ST7538Q power line FSK
transceiver.
With this reference design, it is possible to evaluate the features of the ST7538Q and its
transmitting and receiving performances in an actual communication on the power line
network.
The ST7538Q reference design can be considered as composed of three main sections:
■power supply section, specifically designed to coexist with power line communication and
to operate from a wide-range input mains voltage
■modem and crystal oscillator section
■dual channel line coupling interface section
The dual channel line coupling interface allows the ST7538Q FSK transceiver to transmit
and receive on the mains using two different carrier frequencies: 72 kHz and 86 kHz, both
within the frequency band A specified by the European CENELEC EN50065 standard for
AMR applications.
Figure 1. ST7538Q dual channel reference design board with outline dimensions
As it can be seen from the picture above, a special effort has been made to develop a
compact reference design board, oriented to practical applications.
Note: The information provided in this application note refers to the EVALST7538DUAL reference
design board.
56mm
98mm
www.st.com

Contents AN2744
2/56
Contents
1 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2 Safety precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3 ST7538Q FSK power line transceiver description . . . . . . . . . . . . . . . . 10
4 Evaluation tools description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5 Board description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.1 Line coupling interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
5.1.1 Dual channel selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.1.2 Dual channel Tx passive filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.1.3 Dual channel Rx passive filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.1.4 Dual channel Rx active filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.1.5 Input impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.2 Conducted disturbances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
5.2.1 Conducted emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
5.2.2 Noise immunity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.3 Thermal design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
5.4 Oscillator section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
5.5 Surge and burst protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
5.6 50-pin connector for communication board . . . . . . . . . . . . . . . . . . . . . . . 40
5.7 Power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
6 Performance and ping tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
7 Application ideas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
7.1 Three-phase architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
7.2 Received signal strength indication (RSSI) . . . . . . . . . . . . . . . . . . . . . . . 47
7.3 110-132.5 kHz dual channel coupling circuit . . . . . . . . . . . . . . . . . . . . . . 49
8 Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
9 List of normative references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

AN2744 Contents
3/56
Appendix A Board layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
10 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

List of figures AN2744
4/56
List of figures
Figure 1. ST7538Q dual channel reference design board with outline dimensions. . . . . . . . . . . . . . . 1
Figure 2. Typical curve for output current limit vs. RCL value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Figure 3. ST7538Q transceiver block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figure 4. Complete evaluation system including a PC, an EVALCOMMBOARD and the
EVALST7538DUAL board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Figure 5. Power line modem demonstration kit with transmission session window . . . . . . . . . . . . . . 13
Figure 6. Scheme of the various sections of the board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Figure 7. Modem and coupling interface schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Figure 8. Power supply schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Figure 9. Schematic of Rx and Tx filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Figure 10. Measured frequency response of the Tx passive filter for 72 kHz channel (typical). . . . . . 22
Figure 11. Measured frequency response of the Tx passive filter for 86 kHz channel (typical). . . . . . 23
Figure 12. Simulated frequency response of the Tx passive filter for 72 kHz channel with tolerance
effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Figure 13. Simulated frequency response of the Tx passive filter for 86 kHz channel with tolerance
effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Figure 14. Measured frequency response of the Rx passive filter for 72 kHz channel (typical) . . . . . 25
Figure 15. Measured frequency response of the Rx passive filter for 86 kHz channel (typical) . . . . . 26
Figure 16. Simulated frequency response of the Rx passive filter for 72 kHz channel with tolerance
effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Figure 17. Simulated frequency response of the Rx passive filter for 86 kHz channel with tolerance
effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Figure 18. Measured frequency response of the Rx active filter for 72 kHz channel (typical) . . . . . . . 27
Figure 19. Measured frequency response of the Rx active filter for 86 kHz channel (typical) . . . . . . . 28
Figure 20. Simulated frequency response of the Rx active filter for 72 kHz channel with tolerance
effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Figure 21. Simulated frequency response of the Rx active filter for 86 kHz channel with tolerance
effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Figure 22. Measured input impedance magnitude of the coupling interface in Rx mode for the 72 kHz
channel (typical curve) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Figure 23. Measured input impedance magnitude of the coupling interface in Rx mode for the 86 kHz
channel (typical curve) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Figure 24. Measured input impedance magnitude of the coupling interface in Tx mode for the 72 kHz
channel (typical curve) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Figure 25. Measured input impedance magnitude of the coupling interface in Tx mode for the 86 kHz
channel (typical curve) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Figure 26. Conducted disturbance test setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Figure 27. Output spectrum (typical) at 72 kHz channel, mains 220 VAC, fixed transmitted
tone = "1" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Figure 28. Output spectrum (typical) at 86 kHz channel, mains 220 VAC, fixed transmitted
tone = "1" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Figure 29. Narrowband conducted interference test setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Figure 30. Measured BER vs. SNR curve (typical), white noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Figure 31. Measured SNR vs. frequency curves (typical) at BER=10-3 - 72 kHz channel . . . . . . . . . 35
Figure 32. Measured SNR vs. frequency curves (typical) at BER=10-3 - 86 kHz channel . . . . . . . . . 35
Figure 33. PCB copper dissipating area for the ST7538Q dual channel reference design . . . . . . . . . 36
Figure 34. Packet-fragmented transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Figure 35. Thermal impedance typical curve for the ST7538Q mounted on the reference design
board. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Figure 36. A recommended oscillator section layout for noise shielding . . . . . . . . . . . . . . . . . . . . . . . 38

AN2744 List of figures
5/56
Figure 37. Common mode disturbances protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Figure 38. Differential mode disturbances protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Figure 39. Scheme of the communication board connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Figure 40. Typical waveforms at 230 VAC: open load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Figure 41. Typical waveforms at 230 VAC: full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Figure 42. Typical waveforms at 265 VAC: short-circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Figure 43. Typical waveforms at 265 VAC: startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Figure 44. Load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Figure 45. SMPS efficiency curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Figure 46. Demonstration software window for the master board . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Figure 47. Scheme of principle for three-phase architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Figure 48. Peak detector electrical schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Figure 49. Measured DC_OUT vs. AC_IN peak detector performance . . . . . . . . . . . . . . . . . . . . . . . . 48
Figure 50. PCB layout - top view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Figure 51. PCB layout - bottom view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

List of tables AN2744
6/56
List of tables
Table 1. Electrical characteristics of the ST7538Q dual channel reference design . . . . . . . . . . . . . . 7
Table 2. Output signal level setting through VSENSE partitioning - typical values . . . . . . . . . . . . . . . . 8
Table 3. Bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Table 4. ST parts on the ST7538Q dual channel reference design board . . . . . . . . . . . . . . . . . . . . 19
Table 5. Line coupling transformer specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Table 6. Noise immunity test settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Table 7. 50-pin connector digital signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Table 8. 50-pin connector control signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Table 9. 50-pin connector power connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Table 10. SMPS specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Table 11. SMPS transformer specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Table 12. List of components to be modified for the 110-132.5 kHz dual channel coupling. . . . . . . . 49
Table 13. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

AN2744 Electrical characteristics
7/56
1 Electrical characteristics
Table 1. Electrical characteristics of the ST7538Q dual channel reference design
Parameter Value Notes
Min. Typ. Max.
Operating condition
Ambient operating
temperature 85 °C
If junction temperature
exceeds 180 °C the device
shuts down
Transceiver section
Selectable channel frequencies: 72 kHz (CH1), 86 kHz (CH2)
Transmitting specifications (Tx Mode)
Transmitting output voltage
level 2 VRMS 2.25 VRMS
R20 = 3.9 kΩ, R22=2.2 kΩ
– see Ta b le 2
Transmitting output current
limit 325 mARMS R19 = 2 kΩ– see Figure 2
Second harmonic distortion -55 dB Loaded with CISPR 16-1
network
Third harmonic distortion -61 dB Loaded with CISPR 16-1
network
50 Hz attenuation 100 dB
Receiving specifications (Rx Mode)
Minimum detectable Rx signal 53 dB/µVRMS BER<10-3, negligible noise
Auxiliary supply
5 V linear regulator (VDC)
output voltage -5% 5.05 V +5% ST7538Q internally generated
5 V linear regulator (VDC)
current capability 100 mA
Power supply section
AC mains voltage range 85 V 265 V
Mains frequency 50-60 Hz
Output voltage -10% 10 V +10% Green LED ON
Output voltage ripple 1% IOUT = 600 mA, VIN=85 VAC
Output current 600 mA
Output power 5.6 W
Efficiency at POUT = 3.5 W 70%
Nominal transformer
isolation(1) 4 kV Primary to secondary/ secondary to auxiliary
Number of holdup cycles 0

Electrical characteristics AN2744
8/56
Note: 1 EN50065-1 normative compliance is not guaranteed with a signal level at mains output
greater than 2 VRMS
Parameter Value Notes
Input power 100 mW
Switching frequency -10% 60 kHz +10% Transceiver section in Tx mode
1. ST does not guarantee transformer isolation. ST assumes no responsibility for the consequences that may result from that
risk.
Table 1. Electrical characteristics of the ST7538Q dual channel reference design (continued)
Table 2. Output signal level setting through VSENSE partitioning - typical values
VOUT [VRMS]V
OUT [dBuVRMS](R 7+ R8) / R8R7[kΩ]R 8[kΩ]
1.000 120 1.25 0.910 2.2
1.125 121 1.4 1.3 2.2
1.250 122 1.6 2.2 2.2
1.500 124 2.0 2.7 2.2
1.800 125 2.25 3.3 2.2
2.000 126 2.5 3.9 2.2
2.250 (Note 1) 127 2.8 4.7 2.2
2.500 (Note 1) 128 3.15 6.8 2.2
3.000 (Note 1) 130 4.0 7.5 2.2
Figure 2. Typical curve for output current limit vs. RCL value
100
150
200
250
300
350
400
1.75 2 2.25 2.5 2.75 3 3.25 3.5 3.75 4 4.25 4.5 4.75 5
Rcl (kOhm)
Irms (mA)
100
150
200
250
300
350
400
1.75 2 2.25 2.5 2.75 3 3.25 3.5 3.75 4 4.25 4.5 4.75 5
Rcl (kOhm)
Irms (mA)

AN2744 Safety precautions
9/56
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.

ST7538Q FSK power line transceiver description AN2744
10/56
3 ST7538Q FSK power line transceiver description
The ST7538Q transceiver performs a half-duplex communication over the power line
network using frequency shift keying (FSK) modulation. It operates from a 7.5 to 12.5 V
single supply voltage (PAVCC) and integrates a differential-output power line interface (PLI)
stage and two linear regulators providing 5 V (VDC) and 3.3 V (DVDD).
The ST7538Q can be programmed to communicate using eight different frequency
channels (60, 66, 72, 76, 82.05, 86, 110 and 132.5 kHz), four baud rates (600, 1200, 2400
and 4800 symbols per second) and two frequency deviations (1 and 0.5).
Many auxiliary functions are integrated. The transmission section includes automatic control
on PLI output voltage and current, programmable time-out function and thermal shutdown.
The reception section includes automatic input level control, carrier/preamble detection and
band-in-use signaling.
Additional features are included, such as watchdog timer, zero-crossing detector, internal
oscillator and a general purpose op-amp.
The serial interface (configurable as UART or SPI) allows interfacing to a host
microcontroller, intended to manage the communication protocol. A reset output (RSTO)
and a programmable 4-8-16 MHz clock (MCLK) can be provided to the microcontroller to
simplify the application.
Communication on the power line can be either synchronous or asynchronous with the data
clock (CLR/T) provided by the transceiver at the programmed baud rate.
When in transmission mode (i.e. RxTx line at low level), the ST7538Q transceiver samples
the data on the TxD line, generating an FSK modulated signal on the ATO pin. The same
Figure 3. ST7538Q transceiver block diagram