ST AN1714 APPLICATION NOTE

AN1714

Application note

ST7538Q FSK powerline

transceiver demonstration kit description

Introduction

The advantages in the implementation of a communication network using the same electrical network that supplies all the elements of the network are evident. In the presence of new wideband LANs using an RF system, for example Bluetooth, a narrowband communication system using the mains has considerable advantages also.

It is widely accepted that in residential or industrial areas, in parallel to a wideband network for audio/video streaming and Internet, having a narrowband LAN is useful to carry simple information such as measurements, commands to actuators, system controls and so on.

Many applications can be covered by a narrowband communication system in a residential structure, outside the house or in industrial applications (see Figure 1 below).

Figure 1. Typical powerline modem applications scenario

For example in houses or commercial buildings possible applications are power management, lighting control, heating or cooling system management, remote control of appliances (by internet or telephone), and control of alarm systems.

Considering external applications, the main areas concern communication with meters, in particular automatic measuring and remote control, prepaid supply systems, meter or inhome remote displays. Another relevant industrial segment could be street lighting management.

February 2008 Rev 4 1/46

www.st.com

Contents AN1714

Contents

1 Powerline communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.1 The electrical network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.1.1 Impedance of powerlines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1.1.2 Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1.1.3 Typical connection losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.1.4 Standing waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.2 ST7538Q FSK powerline transceiver description . . . . . . . . . . . . . . . . . . . . 9

2 Demonstration board for ST7538Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.1 Main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.2 Signal coupling interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.2.1 Transmitting section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.2.2 Receiving section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

2.2.3 Voltage regulation-current protection loops . . . . . . . . . . . . . . . . . . . . . . 21

2.3 Board power management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

2.3.1 L6590 regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

2.3.2 ST7538Q power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

2.4 Crystal oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

2.5 Burst and surge protections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

2.6 ST7 microcontroller and RS232 interface . . . . . . . . . . . . . . . . . . . . . . . . 30

2.6.1 Modem / microcontroller interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

2.7 Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

3 Demonstration board characterization . . . . . . . . . . . . . . . . . . . . . . . . . 37

3.1 Conducted disturbance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

3.2 Narrowband conducted interference . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

3.3 Output impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

4 Design ideas for auxiliary blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

4.1 Zero-crossing detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Appendix A Documentation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

4.2 ST7538Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

2/46

AN1714 Contents

4.3 L6590 integrated power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

4.4 ST7 microprocessor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

4.5 Surge and burst protections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

6 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

3/46

List of figures AN1714

List of figures

Figure 1. Typical powerline modem applications scenario. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Figure 2. Mains signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Figure 3. Aggregate European powerline impedance (by Malack and Engstrom). . . . . . . . . . . . . . . . 7

Figure 4. Voltage spectra of a 100 W light dimmer, a notebook PC, a desktop PC, a CFL lamp,

a TLE lamp, all working with a 50 Hz/~220 V supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Figure 5. FSK modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 6. ST7538Q transceiver block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 7. ST7538Q demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 8. Demonstration board layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 9. Demonstration board schematic: microcontroller and PC interface . . . . . . . . . . . . . . . . . . 12

Figure 10. Demonstration board schematic: line coupling interface and power supply . . . . . . . . . . . . 13

Figure 11. Demonstration board ST7538Q powerline interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 12. Demonstration board ST7538Q transmission coupling circuit . . . . . . . . . . . . . . . . . . . . . . 15

Figure 13. Simplified schematic of the transmission filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 14. Simulated characteristics of the transmission coupling filter. . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 15. Coupling circuit with a 2

Figure 16. Demonstration board ST7538Q receiving circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Figure 17. Measured filtering characteristic of the demonstration board at the RAI pin in receive

mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 18. Powerline output characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 19. Voltage regulation and current protection components . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Figure 20. Voltage regulation/current protection loop logic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Figure 21. Current protection loop characteristic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Figure 22. Voltage regulation and current protection feedback signals . . . . . . . . . . . . . . . . . . . . . . . . 24

Figure 23. Power supply EMC disturbances filter circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Figure 24. Noise generation in resistive supply or ground path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Figure 25. A recommended oscillator section layout for noise shielding . . . . . . . . . . . . . . . . . . . . . . . 28

Figure 26. Common mode and differential mode spikes example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Figure 27. Microcontroller/RS232 interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Figure 28. ST7538Q / microcontroller interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Figure 29. Conducted disturbance setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Figure 30. Output signal spectrum, channel 132.5 kHz, mains 220 V~, fixed tone . . . . . . . . . . . . . . . 38

Figure 31. Output signal spectrum, channel 132.5 kHz, mains 220 V~, random sequence . . . . . . . . 38

Figure 32. Output signal spectrum, channel 132.5 kHz, mains 110 V~, random sequence . . . . . . . . 39

Figure 33. Output signal spectrum, channel 110 kHz, mains 220 V~, random sequence . . . . . . . . . . 39

Figure 34. Narrowband conducted interferences setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Figure 35. Signal/noise ratio for the 132.5 kHz channel, signal level 85 dBuV . . . . . . . . . . . . . . . . . . 40

Figure 36. Signal/noise ratio for the 132.5 kHz channel, signal level 85 dBuV, mains 110 V~ . . . . . . 41

Figure 37. Signal/noise ratio for the 110 kHz channel, signal level 91 dBuV. . . . . . . . . . . . . . . . . . . . 41

Figure 38. Output board impedance measurement setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Figure 39. Output demonstration board impedances (CN1) in receiving condition . . . . . . . . . . . . . . . 42

Figure 40. Output demonstration board impedances (CN1) in transmitting condition . . . . . . . . . . . . . 42

Figure 41. Zero-crossing coupling circuit, nonisolated solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Figure 42. Zero-crossing coupling circuit, isolated solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

order band pass butterworth . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

4/46

AN1714 Powerline communication

1 Powerline communication

Although the concepts of power line communication and home automation, as well as the

development of different devices dedicated for power line communication, have been

present for several years, the market segment for this kind of application has only recently

been growing.

The three main factors that have contributed up to now to the field of the powerline

communication are:

a) The slow development of international norms and standards

b) Some technical constraints related to the electrical network

c) General consideration of costs

The first point concerns standards and norms. A general consideration in an open

communication system is to have mandatory rules and guidelines to guarantee that every

node, whatever the manufacturer, does not compromise the characteristics of the entire

network and the performance of the communication system.

For residential products this aspect is quite relevant considering the presence of many

different appliances and manufacturers, and also the concern for a common language (the

protocol) which is mandatory.

In 2002 the CENELEC (European Committee for Electrotechnical Standardizations)

published or updated a series of regulations about communication on low-voltage electrical

installations. We refer in particular to the EN50065-1, concerning general requirements,

frequency bands and electromagnetic disturbances; the EN50065-4-2 about the low-voltage

decoupling filter and safety requirements; and the EN50065-7 about the impedance of the

devices.

A preliminary version (1999) of the EN50065-2-1 about immunity requirements is also

available.

There has been a certain alignment among the appliance manufacturers on the EHS

(European Home System) protocols, even if a lot of customized protocols are present,

mainly in proprietary mains. More information on EHS protocol is available in the EHS

booklet.

The second critical consideration concerns the technical problems regarding the specific

topology of the electrical network.

Figure 2 shows what happens to a signal transmitted on an electrical network. For several

reasons that are listed in the next paragraph (low impedance, different kind of disturbances,

etc.) the received FSK signal has a very low level and it is mixed with a great level of noise.

5/46

Powerline communication AN1714

Figure 2. Mains signals

MAINS

Tx Rx

ST 7538

Received Signal

f f f f

Transmitted Signal

The aspects of noise and low impedance are more critical in a residential house where

many different appliances are present.

Every entity of the network has to be able to manage reliable communication also under

these critical conditions. To achieve this goal all aspects of the application design have to be

carefully considered, from the coupling interface to the power management, from the type of microprocessor to the powerline transceiver, as well as considering their mutual influences.

Last but not least, we must consider the economic point of view. It isn’t a simple calculation of the node cost with respect to an equivalent wireline or wireless solution, but a consideration of other aspects such as the installation and configuration cost of the entire network.

Another economic issue that has to be considered is the power consumption of a single communication node. The power consumption of each communication unit has to be lower as possible because every unit must always stay on ready to receive commands from a remote transmitter. This constraint is even more relevant in applications with a huge number of nodes. Consider for example the control of a street lighting system with thousands of lamps or a metering system with several thousands of electricity meters.

The ST7538Q has been designed considering all issues previously listed. With this device it is possible to obtain highly efficient and reliable applications for powerline communication, characterized by low power consumption, low cost, and compliance with the main norms and protocol currently in place.

1.1 The electrical network

The communication medium consists of everything connected to power outlets. This includes house wiring in the walls of the building, appliance wiring, and the appliances themselves, the service panel, the triplex wire connecting the service panel to the distribution transformer and the distribution transformer itself. Since distribution transformers usually serve more than one residence, the loads and wiring of all residences connected to the same transformer must be included.

6/46

AN1714 Powerline communication

1.1.1 Impedance of powerlines

A powerline has very variable impedance depending on several factors such as its configuration (star connection, ring connection) or the number of entities linked.

Extensive data on this subject has been published by Malack and Engstrom of IBM (Electromagnetic Compatibility Laboratory), who measured the RF impedance of 86 commercial AC power distribution systems in six European countries (see Figure 3).

These measurements show that the impedance of the residential power circuits increases with frequency and is in the range from about 1.5 to 8 Ω at 100 kHz. It appears that this impedance is determined by two parameters - the loads connected to the network and the impedance of the distribution transformer. Recently a third element influences the impedance of the powerline, in particular in residential networks. It is represented by the EMI filters mounted in the last generation of home appliances (refrigerators, washing machines, television sets, stereos). Wiring seems to have a relatively small effect. The impedance is usually inductive.

For typical resistive loads, signal attenuation is expected to be from 2 to 50 dB at 150 kHz depending on the distribution transformer used and the size of the loads. Moreover, it may be possible for capacitive loads to resonate with the inductance of the distribution transformer and cause the signal attenuation to vary wildly with frequency.

For the compliance tests the normative EN50065 use two artificial mains networks conforming to sub clause 11.2 of CISPR 16-1:1993. Measurements on real networks have shown that this artificial network does not truly represent practical network impedance. To better evaluate the performance of a real signaling system, an adaptive network must be used in conjunction with the CISPR 16-1 artificial network. The design of the adaptive circuit is included in the informative annex F of EN50065-1 (revision 2001).

Figure 3. Aggregate European powerline impedance (by Malack and Engstrom)

1.1.2 Noise

Appliances connected to the same transformer secondary to which the powerline carrier system is connected cause the principal source of noise. The primary sources of noise are Triacs used in light dimmers, universal motors, switching power supplies used in small and portable appliances and fluorescent lamps.

IMPEDANCE MAGNITUDE (OHM)

1000.0

100.0

10.0

MAXIMUM

1.0

0.1

0.04 0.08 0.10 0.30 0.75 2.10 5.00 15.00 30.00

FREQUENCY (MHz)

MEAN MINIMUM

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Powerline communication AN1714

Triacs generate noise synchronous with the 50 Hz power signal and this noise appears as harmonics of 50 Hz. Universal motors found in mixers or drills also create noise, but it is not as strong as light dimmer noise, and not generally synchronous with 50 Hz.

Furthermore, light dimmers are often left on for long periods of time whereas universal motors are used intermittently.

In the last years two other sources of strong noise have been introduced in the electrical network. They are Compact Fluorescent Lamps (CFL) and the switching power supplies of rechargeable battery (for example notebook PCs) or small appliances.

In many cases they have a working frequency or some harmonics in the range of the powerline communication band (from 10 kHz to 150 kHz). Of course the presence of continuous tones exactly at communication channel frequency can affect the reliability of communication.

The Figure 4 shows some of the noise sources we refer to. The measurement setup consists of an insulation transformer with a VARIAC, a spectrum analyzer HP4395A coupled by a high voltage capacitor (1µF) and a 2 mH transformer (1:1).

Figure 4. Voltage spectra of a 100 W light dimmer, a notebook PC, a desktop PC, a

CFL lamp, a TLE lamp, all working with a 50 Hz/~220 V supply

dBuV

110.0

90.0

70.0

50.0

30.0

10.0

Background CFL 11W Desktop PC Dimmer 100W TLE 22W Notebook PC

1.00E+03 1.00E+04 1.00E+05 1.00E+06

1.1.3 Typical connection losses

The transmitting range of a home automation system depends on the physical topology of the electric power distribution network inside the building where the system is installed.

Different connection losses can be measured. For communication nodes connected to the same branch circuit from transmitter to receiver a typical connection loss is about 10-15 dB. If transmitter and receiver are in different branches of the circuit, separated for example by a service panel, there is an additional attenuation of 10-20 dB.

In some worst-case conditions (socket with very low impedance) the attenuation of the transmitted signal can reach a value of 50-60 db.

1.1.4 Standing waves

Standing wave effects begin to occur when the physical dimensions of the communication medium are similar to about one-eighth of a wavelength, which are about 375 and 250

8/46

AN1714 Powerline communication

meters at 100 and 150 kHz respectively. Primarily the length of the triplex wire connecting the residences to the distribution transformer determines the length of the communication path on the secondary side of the power distribution system. Usually, several residences use the same distribution transformer. It would be rare that a linear run of this wiring would exceed 250 meters in length although the total length of branches might occasionally exceed 250 meters. Thus standing wave effects would be rare at frequencies below 150 kHz for residential wiring.

1.2 ST7538Q FSK powerline transceiver description

The ST7538Q transceiver performs a half-duplex communication over the powerline network using Frequency Shift Keying (FSK) modulation. The FSK modulation technique translates a digital signal into a sinusoidal signal that can have two different frequency values, one for the high logic level of the digital signal (f (f

), as depicted in Figure 5.

Figure 5. FSK modulation

), the second one for the low level

The average value of the two tones is the carrier frequency (f

). The difference or distance

between the two frequencies is a function of the baud-rate (BAUD) of the digital signal (the number of symbols transmitted in one second) and of the deviation (dev). The relationship is:

Equation 1

fHfL– BAUD dev–=

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).

The device operates from a 7.5 to 12.5 V single supply voltage (PAVcc) and integrates a differential-output PowerLine Interface (PLI) stage and two linear regulators providing 5 V (VDC) and 3.3 V (DVdd).

Many auxiliary functions are integrated. The transmission section includes automatic control on PLI output voltage and current, programmable timeout 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 a 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.

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Powerline communication AN1714

Communication on the powerline 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 signal is fed into the differential power amplifier to get four times the voltage swing and a current capability up to 370 mA rms.

When in Reception mode (i.e. RxTx line at high level), an incoming signal at the RAI line is demodulated and converted in a digital bit stream on the RxD pin.

The internal Control Register, which contains the operating parameters of the ST7538Q transceiver, can be programmed only using the SPI interface. The Control Register settings include the Header Recognition and Frame Length Count functions, which can be used to apply byte and frame synchronization to the received messages.

Figure 6. ST7538Q transceiver block diagram

For a more detailed and complete description of the ST7538Q device please refer to the product datasheet.

10/46

AN1714 Demonstration board for ST7538Q

2 Demonstration board for ST7538Q

2.1 Main features

The ST7538Q demonstration board implements in a two layer PCB a complete powerline communication node, including the powerline coupling circuits, a power supply section, a microcontroller and a RS232 serial interface to connect the board to a personal computer (Figure 8). This board with the related firmware load in the ST microprocessor and the PC software is a complete reference for the mains aspects of powerline communications.

Figure 7. ST7538Q demonstration board

Figure 8. Demonstration board layout

LV HV

LV HVLV HV

Power Supply

PC Interface

ST7538P

ST7

The aim of this board is to give a useful tool to develop and to evaluate a powerline application with the device ST7538Q. So even if aspects of the board concerning size and cost aren't optimized, its schematic gives a good design reference and a valid starting point

ST7538P

Signal Coupling

Interface

LV HV

11/46

Demonstration board for ST7538Q AN1714

to develop powerline modem applications. Moreover the board structure (a lot of jumpers, test points, few SMD components) allows easily connecting test probes to take measures and signal verifications, as well as customizing the application according to specific requirements.

Figure 9. Demonstration board schematic: microcontroller and PC interface

TXD

D13

1N4148

MICRO_TXD

H_S

RS232_OUT

RS232_IN

R1IN_A

T1OUT_A

5V_232

C24 100nF C23 100nF

5V_ P

RESET

RS232_OUT

MCLK

ISPSEL

PA7

PA6

PA5

PA4

RS232_IN

CLRT

TOUT

REG_OK

H_S

REG/DATA

RXTX

ZCOUT

JP1

R2OUT

T2IN

T1IN

R1OUT

R1IN

T1OUT

VCC

GND

OSCOUT

VDD_2

RESET

PE0/TD0

OSCIN

ISPSEL

(HS)PA7

(HS)PA6

(HS)PA5

(HS)PA4

PE1/RDI

ANI0/PD0

ANI3/PD3

ANI4/PD4

ANI5/PD5

MCO/PF0

PB0

PB1

PB2

PB3

VDDA

PF2

VSSA

R16

4.7K

ST232

5V_ P

C28

C29

C30

C27

100nF

R2IN

T2OUT

C2-

C2+

C1-

C1+

V-

100nF

T2OUT_A

C26

100nF

C25

100nF

C32

100nF

V+

10 F

CN5

FEMALE

PC INTERFACE

C31

100nF

R1IN_A

T1OUT_A

T2OUT_A

RN1

TOUT

VDD_1

ST2334N2

PA3

PC7/SS

PC6/SCK/ISPCLK

PC5/MOSI

PC3/ICAP1_B(HS)

PC4/MSO/ISPDATA

PC2/ICAP2_B(HS)

PC1/OCMP1/B

PC0/OCMP2/B

EXTCLK_A(HS)

ICAP1_A/PF6(HS)

OCMP1_A/PF4

PF1/BEEP

AN2/PD2

AN1/PD1

PB4

VDD_0

VSS_0

VSS_1

VSS_2

5V_ P5V_ P

CN7

ISP INTERFACE

COMMON

D11

D10

RED

YELLOW

CD/PD

PA4 PA5 PA6 PA7

5V_ P

CD/PD

ISPCLOCK

CLRT

J11

RXD

ISPDATA

MICRO_TXD

5V_ P

D03IN1450

5V_led

J10

CN6

R17 10K

ISPDATA

ISPCLOCK

RESET

ISPSEL

D12

GREEN

5V_232

5V_led

5V_ P

RED

12/46

AN1714 Demonstration board for ST7538Q

Figure 10. Demonstration board schematic: line coupling interface and power

supply

5.1Ω

ATOP2

VDCAVDDTEST1

N.C.

4096-X046

VAC T60403-

D16

P6KE6V8A

C13 220nF

50K

R12

TRIM

VSENSE

ATOP1

RXFO29TEST2

332835

RXD

CD/PD

CPLUS

CMINUS

RXD

CD/PD

VSENSE

D03IN1451

C36

4.7nF

330H

750

R11

P10V

C38

10 F

R14

C17

5.6nF/63V

C21

100nF

JPTIN

AVSS25PAVCC22PAVSS

GND

ST7538P

C_OUT

RxTx

Rx/Tx

TXD

REG_OK

TXD

REG_DATA

REG_OK

C18 47pF

XIN

RSTO

R15 4.7K

REG/DATA

RESET

C33

10nF

C37

100pF

TO GND

C19 18pF

SOLD CRYSTAL CASE

ZCOUT

16MHz

ZCOUT

RAI

XOUT

GND

DVSS

DVDD

SW1

C20

C22

22nF

300nF

CLRT

TIMEOUT

CLRT

ATO

13 16

R13

ZCIN

N.C.

N.C. N.C. TEST3

MCLK

TRIM

JP16

JP13

P10V

TR1

RADIOHM 69E16H1B

L2 220 H

1.5A W04

47nF

R1 16.2 2W

L5 1mH

F1 TR5-F 0.5A

CN1

CN4

L3 10 H

STPS160ASMA

BZW06-

4.7 F

L1 42V15

400V

ACLINE

234

ZCIN

CN2

171

400V

2 x 10mA

0.3A RADIOHM

to 256V

85V

ZCOUT

281

STTA106

DRAIN

ATOP1

470 F

C34

VCC

L6590

ATOP2

2.2K

16V

100nF

GND

RXFO

D6 1N4148

R3 10

ATO

GREEN

50V

22 F

GND

D7 1N4148

R5 3.3K RL6 10

VFB

GND

CN3

4.7M

220V X2

C11 33nF

L4 22 H

1T1T

D17

SM6T6V8A

D15

P6KE6V8A

R10

C_R9

100nF

LC12 10 H

JP36

C15

100nF

C10

910

VCOMP

C14

10 F

10 H

C16

100nF

JP35

2.2nF/Y1

2.2 Signal coupling interface

The line signal interface links the application board to the mains, obtaining a highly efficient coupling circuit for the received and transmitted FSK signals and a reliable filtering system for the mains voltage (220 V~/50 Hz or 110 V~/60 Hz), for noise and for bursts or surges.

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Demonstration board for ST7538Q AN1714

It is possible to implement different topologies of coupling circuits. A first classification is between an isolated solution with a line transformer or a double capacitor and a nonisolated solution with a single high-voltage decoupling capacitor. The last one is simpler and cheaper, while the first one achieves better performances using efficiently the differential power output of the devices.

The differential solution has been also preferred for the advantage in reducing the even harmonics of the transmitted signals.

Figure 11. Demonstration board ST7538Q powerline interface

ST7538

RAI

ATO P1

ATOP2

Rx Band Pass Filter

C33

C36

C13

LC12

Tx Band Pass Filter

R11

R10

CR9

D16

D15

Protections

D17

Tx Band Pass Filter

1:1

1:11:1

C11

MAINS

In the design of the coupling interface many technical and standard constraints have to be considered that are different in a receiving condition with respect to a transmitting status.

Following is a list of design specifications for signal coupling for the European market:

● High selectivity in receiving mode (EN50065-2-1)

● Output impedances as great as possible (EN50065-7)

● Low noise in receiving mode

● Wide voltage and current signal compatibility in every condition (EN50065-1)

● Very low distortion in transmission mode (EN50065-1)

● High coupling efficiency in transmission mode (also with high loads)

● High reliability to burst and surge spikes (EN50065-2-1)

A series of constraints listed in EN50065-4-2, "Low voltage decoupling filters - Safety requirements", have to be guaranteed by the decoupling elements (transformer or capacitors) in order to be compliant with a

4 kV or 6 kV class.

The solution implemented in the demonstration board is an isolated circuit with a 1:1 transformer and a X2 class capacitor. In the chosen topology the transmission sections components do not have any relevant influences on the receiving circuits, so the two structures can be analyzed separately. The component values that consitute the passive filters have been dimensioned for the 132.5 kHz channel, but also with the 110 kHz communication frequency, the performances of the board meet the requirement for reliable communication.

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