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 2nd order band pass butterworth. . . . . . . . . . . . . . . . . . . . . . . . . . . 18 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

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
	Rx			Tx
	ST 7538			ST 7538
Received Signal					Transmitted Signal

f	f	f
fc		fc

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 to 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.

1.1The 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

1.1.1Impedance 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)

IMPEDANCE MAGNITUDE (OHM)

1000.0
100.0
10.0
						MAXIMUM
1.0						MEAN
						MINIMUM
0.1
0.04	0.08	0.10	0.30	0.75	2.10	5.00	15.00	30.00

FREQUENCY (MHz)

1.1.2Noise

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.

7/46

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	Background
	CFL 11W
30.0	Desktop PC
	Dimmer 100W
	TLE 22W
10.0	Notebook PC
1.00E+03		1.00E+04	Hz	1.00E+05	1.00E+06

1.1.3Typical 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.

1.1.4Standing 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.

1.2ST7538Q 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 (fH), the second one for the low level (fL), as depicted in Figure 5.

Figure 5. FSK modulation

The average value of the two tones is the carrier frequency (fC). 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

fH – fL = 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.

9/46

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

2.1Main 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

Power Supply

PC Interface

ST7538P

ST7

Q

Signal

Coupling

Interface

LV

LV

HV

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

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

5V_ P

CN7

1

2

ISPDATA

3

4

ISPCLOCK

R16

C27

C28

C29

C30

C31

5

6

RESET

D13

4.7K

JP1

100nF

100nF

100nF

10 F

100nF

5V

7

8

ISPSEL

1N4148

9

10

R17

ISP INTERFACE

10K

MICRO_TXD

U3

CN5

R2IN

FEMALE

RN1

R2OUT

8

COMMON

9

T2OUT

5

1

5V_led

T2IN

7

T2OUT_A

R4

H_S

10

9

5

T1IN

5

R3

RS232_OUT

11 ST232

C2-

4

4

R1OUT

C26

R2

RS232_IN

R1IN

12

4

C2+

100nF

8

3

R1

R1IN_A

13

R1IN_A

2

T1OUT

3

3

T1OUT_A

14

C1-

7

D11

D10

D12

D9

C25

5V_232

VCC

16

C1+

T1OUT_A

RED

YELLOW

GREEN

RED

GND

1

100nF

2

TOUT

CD/PD

RX

TX

15

V-

6

2

6

T2OUT_A

PA4

PA5

PA6

PA7

V+

C32

1

PC INTERFACE

100nF

J10

C24 100nF

C23 100nF

5V_232

5V

J9

5V_led

U4

J8

5V_ P

OSCOUT

41

32

VDD_1

5V_ P

VDD_2

PA3

5V_ P

43

31

CD/PD

RESET

PC7/SS

RESET

39

30

SS

PE0/TD0

RS232_OUT

44

ISPCLOCK

OSCIN

PC6/SCK/ISPCLK

MCLK

42

29

CLRT

ISPSEL

J11

ISPSEL

38

PC5/MOSI

(HS)PA7

28

RXD

PA7

37

PC3/ICAP1_B(HS)

(HS)PA6

26

ISPDATA

PA6

36

PC4/MSO/ISPDATA

(HS)PA5

27

MICRO_TXD

CN6

PA5

35

(HS)PA4

PC2/ICAP2_B(HS)

12

PA4

34

25

PE1/RDI

PC1/OCMP1/B

11

RS232_IN

1

24

PB0

PC0/OCMP2/B

10

SS

2

ST2334N2

23

PB1

EXTCLK_A(HS)

7

CLRT

3

20

PB2

ICAP1_A/PF6(HS)

6

TOUT

4

19

PB3

OCMP1_A/PF4

4

REG_OK

5

18

ANI0/PD0

PF1/BEEP

BU

8

H_S

7

16

ANI3/PD3

AN2/PD2

3

WD

10

9

ANI4/PD4

AN1/PD1

5

REG/DATA

11

8

ANI5/PD5

PB4

9

RXTX

12

6

VDDA

VDD_0

2

5V_ P

13

21

PF2

5V_ P

1

ZCOUT

17

22

VSS_0

5V_ P

MCO/PF0

VSS_1

PG

15

33

VSSA

VSS_2

14

40

D03IN1450

12/46

.surgesorburstsforandnoiseforHz),V~/60 110 or Hz V~/50 (220 voltage mains the for

systemfilteringreliableaandsignalsFSKtransmitted and received the for circuit coupling

efficienthighlyaobtainingmains,thetoboard application the links interface signal line The

2.2

powerandinterfacecouplinglineschematic: board Demonstration .10 Figure

AN1714

13/46

interface coupling Signal

L5 1mH

R1 16.2 2W

supply

ST7538QforboardDemonstration

F1 TR5-F 0.5A

D1

CN1

1.5A W04

TR1

1

C1

L2 220 H

P

RADIOHM 69E16H1B

N

47nF

D3

4

D2

P10V

2

400V

L1 42V15

C2

C3

BZW06-

STPS160ASMA

ACLINE

2 x 10mA

4.7 F

4.7 F

171

L3 10 H

CN4

85VAC to 256VAC

0.3A RADIOHM

400V

400V

7

ZCIN

1

D4

J1

CN2

ZCOUT

2

DRAIN

STTA106 2

C4

C5

1

3

L6590

1

VCC

C34

470 F

470 F

R2

ATOP1

100nF

2.2K

4

3

16V

16V

2

ATOP2

GND

6

C6

R3 10

D6 1N4148

1

D5

RXFO

5

GND

22 F

8

GREEN

6

GND

7

U1

VFB

50V

R5 3.3K

RL6 10 D7 1N4148

ATO

7

8

5

3

4

R7

C10

VCOMP

C8

910

1 F

1 F

5V

LC12 10 H

L4 22 H

L8

T2

C7

10 H

C14

C15

D15

C11 33nF

CN3

2.2nF/Y1

C16

10 F

100nF

C_R9

P6KE6V8A

220V X2

1

JP35

100nF

JP36

D17

1T

1T

4.7M

TEST1

N.C.

AVDD

VDC

ATOP2

R10

SM6T6V8A

2

CMINUS

35

17

28

33

21

5.1Ω

D16

37

ATOP1

P6KE6V8A

J2

CD/PD

CD/PD

1

19

VAC T60403-

J4

RXD

R12

C13 220nF

4096-X046

P

RXD

3

31

RXFO

50K

J5

CPLUS

VSENSE

TRIM

N

38

29

R11

J3

C_OUT

TEST2

JPTIN

C17

R14

750

C_OUT

RxTx

40

30

GND

5.6nF/63V

1K

Rx/Tx

4

6

TXD

L7

C36

5V

5

AVSS

TXD

REG_OK

25

330 H

4.7nF

J6

REG_OK

36

C38

PG

C21

VSENSE

42

ST7538QP

10 F

PG

REG_DATA

22

PAVCC

100nF

P10V

CL

REG/DATA

43

U2

PAVSS

20

R15 4.7K RSTO

C18 47pF

RESET

12

XIN

27

C22

GND

SW1

41

1x

SOLD CRYSTAL CASE

J7

22nF

XOUT

16MHz

TO GND

DVDD

26

C33

5V

10

DVSS

RAI

C19 18pF

10nF

C20

18

32

DVSS

ZCOUT

300nF

2

15

ZCOUT

TIMEOUT

WD

TIMEOUT

7

14

WD

CLRT

CL

CLRT

8

23

BU

ATO

BU

9 11

39

34

44

13

16

24

ATO

C37

R13

MCLK

MCLK

N.C.

N.C.

N.C.

TEST3

ZCIN

100pF

5K

JP13

JP16

TRIM

5V

D03IN1451

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

Q		Rx Band Pass Filter
ST7538
	C33	R11
RAI	32
		L7
	C36
				Tx Band Pass Filter
				L4	C11
ATOP1	19			1:1
	C13	R10	D16		MAINS
				D17
					R8
		CR9	D15
	21
ATOP2		LC12		T1
			Protections
	Tx Band Pass Filter

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.

14/46