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
56mm
98mm
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.
Rev 1
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April 2008
Contents
AN2744
Contents
1
2
3
4
5
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Safety precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
ST7538Q FSK power line transceiver description . . . . . . . . . . . . . . . . 10
Evaluation tools description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Board description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.1
Line coupling interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
5.1.1
5.1.2
5.1.3
5.1.4
5.1.5
Dual channel selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Dual channel Tx passive filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Dual channel Rx passive filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Dual channel Rx active filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Input impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.2
Conducted disturbances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
5.2.1
5.2.2
Conducted emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Noise immunity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.3
5.4
5.5
5.6
5.7
Thermal design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Oscillator section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Surge and burst protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
50-pin connector for communication board . . . . . . . . . . . . . . . . . . . . . . . 40
Power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
6
7
Performance and ping tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Application ideas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
7.1
7.2
7.3
Three-phase architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Received signal strength indication (RSSI) . . . . . . . . . . . . . . . . . . . . . . . 47
110-132.5 kHz dual channel coupling circuit . . . . . . . . . . . . . . . . . . . . . . 49
8
9
Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
List of normative references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
2/56
AN2744
Contents
Appendix A Board layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
10
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
3/56
List of figures
AN2744
List of figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
Figure 17.
Figure 18.
Figure 19.
Figure 20.
Figure 21.
Figure 22.
Figure 23.
Figure 24.
Figure 25.
Figure 26.
Figure 27.
Figure 28.
Figure 29.
Figure 30.
Figure 31.
Figure 32.
Figure 33.
Figure 34.
Figure 35.
Figure 36.
4/56
ST7538Q dual channel reference design board with outline dimensions . . . . . . . . . . . . . . . 1
Typical curve for output current limit vs. RCL value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
ST7538Q transceiver block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Complete evaluation system including a PC, an EVALCOMMBOARD and the
EVALST7538DUAL board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Power line modem demonstration kit with transmission session window . . . . . . . . . . . . . . 13
Scheme of the various sections of the board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Modem and coupling interface schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Power supply schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Schematic of Rx and Tx filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Measured frequency response of the Tx passive filter for 72 kHz channel (typical). . . . . . 22
Measured frequency response of the Tx passive filter for 86 kHz channel (typical). . . . . . 23
Simulated frequency response of the Tx passive filter for 72 kHz channel with tolerance
effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Simulated frequency response of the Tx passive filter for 86 kHz channel with tolerance
effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Measured frequency response of the Rx passive filter for 72 kHz channel (typical) . . . . . 25
Measured frequency response of the Rx passive filter for 86 kHz channel (typical) . . . . . 26
Simulated frequency response of the Rx passive filter for 72 kHz channel with tolerance
effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Simulated frequency response of the Rx passive filter for 86 kHz channel with tolerance
effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Measured frequency response of the Rx active filter for 72 kHz channel (typical) . . . . . . . 27
Measured frequency response of the Rx active filter for 86 kHz channel (typical) . . . . . . . 28
Simulated frequency response of the Rx active filter for 72 kHz channel with tolerance
effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Simulated frequency response of the Rx active filter for 86 kHz channel with tolerance
effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Measured input impedance magnitude of the coupling interface in Rx mode for the 72 kHz
channel (typical curve) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Measured input impedance magnitude of the coupling interface in Rx mode for the 86 kHz
channel (typical curve) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Measured input impedance magnitude of the coupling interface in Tx mode for the 72 kHz
channel (typical curve) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Measured input impedance magnitude of the coupling interface in Tx mode for the 86 kHz
channel (typical curve) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Conducted disturbance test setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Output spectrum (typical) at 72 kHz channel, mains 220 VAC, fixed transmitted
tone = "1" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Output spectrum (typical) at 86 kHz channel, mains 220 VAC, fixed transmitted
tone = "1" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Narrowband conducted interference test setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Measured BER vs. SNR curve (typical), white noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Measured SNR vs. frequency curves (typical) at BER=10-3 - 72 kHz channel . . . . . . . . . 35
Measured SNR vs. frequency curves (typical) at BER=10-3 - 86 kHz channel . . . . . . . . . 35
PCB copper dissipating area for the ST7538Q dual channel reference design . . . . . . . . . 36
Packet-fragmented transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Thermal impedance typical curve for the ST7538Q mounted on the reference design
board. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
A recommended oscillator section layout for noise shielding . . . . . . . . . . . . . . . . . . . . . . . 38
AN2744
Figure 37.
Figure 38.
Figure 39.
Figure 40.
Figure 41.
Figure 42.
Figure 43.
Figure 44.
Figure 45.
Figure 46.
Figure 47.
Figure 48.
Figure 49.
Figure 50.
Figure 51.
List of figures
Common mode disturbances protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Differential mode disturbances protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Scheme of the communication board connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Typical waveforms at 230 VAC: open load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Typical waveforms at 230 VAC: full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Typical waveforms at 265 VAC: short-circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Typical waveforms at 265 VAC: startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
SMPS efficiency curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Demonstration software window for the master board . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Scheme of principle for three-phase architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Peak detector electrical schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Measured DC_OUT vs. AC_IN peak detector performance . . . . . . . . . . . . . . . . . . . . . . . . 48
PCB layout - top view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
PCB layout - bottom view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
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