ST7537HS1

HOME AUTOMATION MODEM

June 1995

RSTO

RxD

TxD

Rx/Tx

RAI

EST

PAFB

ATO

PABC

TEST1

TEST2

TxIFI

-
01

.
E

PIN CONNECTIONS

PLCC28

(Plastic Chip Carrier)

ORDER CODE : ST7537HS1

HALF DUPLEX ASYNCHRONOUS 2400bps
FSK MODEM

Tx CARRIER FREQUENCY SYNTHESIZED
FROM EXTERNAL CRYSTAL

LOW DISTORTION Tx SIGNAL

Rx SENSITIVITY BETTER THAN 1mV

RMS

CARRIER DETECTION

WATCH-DOG INPUT

RESET AND MASTER CLOCK OUTPUTS
FOR MICROCONTROLLER

POWER AMPLIFIER BIAS CURRENT CON-
TROL (HIGH IMPEDANCE IN Rx MODE)

SIMPLE AND ECONOMICAL APPLICATION
SCHEMATICS

COMPATIBLE WITH CENELEC EN 50065-1
AND FCC SPECIFICATION

CARRIER DETECT CLAMPING ON RxD
PROGRAMMABLE (ALLOWING DEMODULA-
TION ON VERY LOW RECEIVE LEVEL,
1mV

RMS

TYPICALLY)

DESCRIPTION

The ST7537HS1 is a half duplex asynchronous
FSK MODEM designed for home automation com-
munication on the domestic electric mains which
complies with the EN 50065-1 CENELEC stand-
ard.

It mainly operates from a 10V power supply and a
5V power supply for the microcontroller digital in-
terface.

It is interfaced to the power line by an external
driver, and a transformer (see Application Sche-
matic Diagram). Its data transmission rate is
2400 bps and its carrier frequency is 132.45kHz.

1/9

PIN DESCRIPTION

Pin

Name

Pin

Number

Pin

Type

Description

Analog

Common Mode Voltage

Supply

Analog Power Supply : 10V

�

5 %

RAI

Analog

Receive Analog Input

RxFO

Analog

Receive Filter Output

TxIFI

Analog

Transmit and Intermediate Frequency Filters Test Input (mode TEST3)

PAFB

Analog

Power Amplifier Feed-back Input

ATO

Analog

Analog Transmit Output

PABC

Digital (10V)

Power Amplifier Bias Current Control Complementary Output

PABC

Digital (10V)

Power Amplifier Bias Current Control Output

TEST1

Digital

Tx to Rx Automatic Mode Switching Control Input

TEST2

Digital

Automatic Mode Switching Time and Watch-dog Time Reduction Control Input

TEST3

Digital

TxIFI Selection Input

TEST4

Digital

Undelayed Reset Input

Supply

Digital Power Supply : 10V

�

Supply

Digital Ground : 0V

XTAL1

Digital (10V)

Crystal Oscillator Input

XTAL2

Digital (10V)

Crystal Oscillator Output

MCLK

Digital

Master Clock Output

Digital

Watch-dog Input

Rx/Tx

Digital

Rx or Tx Mode Selection Input

Digital

Carrier Detect Output

TxD

Digital

Transmit Data Input

RxD

Digital

Receive Data Output

RSTO

Digital

Reset Output

Supply

Digital Buffers Supply Voltage : 5V

�

5 %

IFO

Analog

Intermediate Frequency Filter Output

DEMI

Analog

Demodulator Input

Supply

Analog Ground : 0V

-
01

.
T

ST7537HS1

2/9

REFERENCE

VOLTAGE

CARRIER

DETECTION

A.A.

FILTER

Rx BAND-PASS

S.C. FILTER

SMT.

FILTER

A.A. FILTER

SMT.

FILTER

Tx BAND-PASS

S.C. FILTER

OUTPUT

AMPLIFIER

CORRELATOR

POST-DEMO

S.C. FILTER

FSK DEMODULATOR

FSK

MODULATOR

CONTROL LOGIC

TIME BASE

RESET LOGIC

A.A. FILTER

SMT.

FILTER

I.F. BAND-PASS

S.C. FILTER

20dB GAIN

RAI

RxFO

ATO

PAFB

PABC

RxD

IFO

XTAL1

XTAL2

MCLK

RSTO

Rx/Tx

TxD

DEMI

TxIFI

TEST LOGIC

TEST1

TEST2

TEST3

TEST4

ST7537HS1

-
02

.
E

BLOCK DIAGRAM

TRANSMIT SECTION

The transmit mode is set when Rx/Tx = 0, if Rx/Tx
is held at 0 longer than 1 second, then the device
switches automatically in the Rx mode. A new
activation of the Tx mode requires Rx/Tx to be
returned to 1 for a minimum 2 microsecond period
before being set to 0.
The Transmit Data (TxD) enter asynchronously the
FSK modulator with a nominal intra-message data
rate of 2400 bps.
The basic transmit frequencies are :
- f(TxD=0) = 133.05kHz
- f(TxD=1) = 131.85kHz
These frequencies are synthesized from a
11.0592MHz crystal oscillator; their precision is the
same as the crystal one's (100ppm).
The modulated signal coming out of the FSK modu-
lator is filtered by a switched-capacitor band-pass
filter (Tx band-pass) in order to limit the output
spectrum and to reduce the level of harmonic com-
ponents.
The final stage of the Tx path consists of an opera-
tional amplifier which needs a feed-back signal
(PAFB) from the power amplifier as shown on
Application Schematic Diagram.
In Tx mode the Receive Data (RxD) signal is set to 1.

RECEIVE SECTION

The receive section is active when Rx/Tx = 1.

The Rx signal is applied on RAI and filtered by a
band-pass switched capacitor filter (Rx band-pass)
centered on the carrier frequency and whose band-
width is around 12kHz.

The Rx filter output is amplified by a 20dB gain
stage which provides symetrical limitations for
large voltage. The resulting signal is down-con-
verted by a mixer which receives a local oscillator
synthesized by the FSK modulator block. Finally an
intermediate frequency band-pass filter (IF band-
pass) whose central frequency is 5.4kHz improves
the signal to noise ratio before entering the FSK
demodulator.

The coupling of the intermediate frequency filter
output (IFO) to the FSK demodulator input (DEMI)
is made by an external capacitor C5 (100nF

�

10%,

10V) which cancels the Rx path offset voltage.

The RxD output delivers the demodulated signal if
the carrier detect (CD) signal is low and is set to
high level when CD = 1.

The RxD output can delivers the demodulated
signal whatever the level of CD (0 or 1) if Rx/Tx = 1
and TxD = 0 (see Figure 1).

ST7537HS1

3/9

ADDITIONAL DIGITAL AND ANALOG FUNC-
TIONS
Time base

A time base section delivers all the internal clocks
from a crystal oscillator (11.0592MHz). The crystal
is connected between XTAL1 and XTAL2 pins and
needs two external capacitors C3 and C4 (22pF

�

10%, 10V) for proper operation.

Reset and watch-dog

The reset output (RSTO) is driven high when the
supply voltage is lower than Vrh (typically 7.6V) with
an hysteresis Vrh-Vrl (typically 300mV) or when no
negative transition occurs on the watch-dog input
(WD) for more than 1.5 second (see the timing
chart on Figure 2). When a reset occurs RSTO is
held high for at least 50ms.

Signal detection

The Carrier Detect output (CD) is driven low when
the input signal amplitude on RAI is greater than
V

for at least T

(typically 6ms see the timing

chart on Figure 3). When the input signal desap-
pears or becomes lower than V

, CD is held low

for at least Tcd before returning to a high level. V

is the carrier detection threshold voltage which is
set internally to detect 5mV

RMS

typically.

External power amplifier bias control

Two dedicated digital output (PABC and PABC)
delivering a signal between 0V and 10V are driven

low respectively high, when the circuit is set in the
receive mode (Rx/Tx=1) or when the transmit mode
time out (1 second) is exceeded; in the same time
the output ATO is put in a high impedance state.

TESTING FEATURES

- An additionnal amplifier allows the observation of

the Rx band-pass filter output on pin RxFO.

- A direct input to the Tx band-pass filter and to the

IF filter (TxIFI) is selected when TEST3 = 1.

- The 1 second normal duration of the Tx to Rx

mode automatic switching is reduced to 488

�

and the 1.5 second watch-dog time out is reduced
to 46.3

�

s when TEST2 = 1.

- When TEST1 = 1 the Tx to Rx mode automatic

switching is desactivated and the functional mode
of the circuit is fully controlled by Rx/Tx.

- TEST4 is a reset input which allows an undelayed

control of RSTO and of the internal state of the
circuit.

POWER SUPPLIES WIRING PRECAUTIONS

The ST7537HS1 has two positive power supply
terminals (AV

,DV

) and two ground terminals

(AV

,DV

) in order to separate internal analog

and digital supplies. The analog and digital termi-
nals of each supply pair must be connected to-
gether externally for proper operation.
The V

must be protected against short-circuit for

proper operation.

Rx/Tx

TxD

RxD

DATA

-
03

.
E

Figure 1 : Data Timing Chart

ST7537HS1

4/9

ABSOLUTE MAXIMUM RATINGS

Symbol

Parameter

Value

Unit

/DV

Supply Voltage (1)

- 0.3, + 12

Digital Input Voltage

- 0.3, DV

+ 0.3

Digital Output Voltage (microcontroller interface)

- 0.3, DV

+ 0.3

Digital Output Voltage (PABC and PABC)

- 0.3, DV

+ 0.3

Digital Output Current

- 5, + 5

Analog Input Voltage

- 0.3, AV

+ 0.3

Analog Output Voltage

- 0.3, AV

+ 0.3

Analog Output Current

- 5, + 5

Power Dissipation

500

oper

Operating Temperature

0, + 70

stg

Storage Temperature

- 55, + 150

-
02

.
T

Notes :

The voltages are referenced to AV

and DV

Absolute maximum ratings are values beyond which damage to device may occur. Functional operation under
these conditions is not implied.

GENERAL ELECTRICAL CHARACTERISTICS

(A/DV

= 10V, A/DV

= 0V, DV

= 5V and 0

amb

C, unless otherwise specificied)

Symbol

Parameter

Test Conditions

Min.

Typ.

Max.

Unit

Supply Voltage

9.5

10.5

Supply Current

Digital Output Supply Voltage

4.75

5.25

Digital Output Supply Current

1.5

High Level Input Voltage

Digital Inputs

4.2

Low Level Input Voltage

Digital Inputs

0.8

High Level Output Voltage

= -100

�

Digital Outputs

�

Digital Outputs PABC and PABC

4.9
9.8

V
V

Low Level Output Voltage

= 100

�

Digital Outputs

�

Digital Outputs PABC and PABC

0.1
0.2

V
V

Duty Cycle

MCLK Output, C

= 15pF

-
0

.
T

TRANSMITTER ELECTRICAL CHARACTERISTICS

(A/DV

= 10V, A/DV

= 0V, DV

= 5V and 0

amb

C, unless otherwise specificied)

Symbol

Parameter

Test Conditions

Min.

Typ.

Max.

Unit

VTAC

Max Carrier Output AC Voltage

= 5.6k

(AV

) = 5.6k

R(ATO, PAFB) = 1k

0.8

1.0

1.3

RMS

HD2

Second Harmonic Distortion

- 50

HD3

Third Harmonic Distortion

- 60

FSK Peak-to-peak Deviation

1200

-
0

.
T

ST7537HS1

5/9

Электронный компонент: ST7537HS1