AN1714 datasheet(9/46 Pages) STMICROELECTRONICS

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AN1714

Powerline communication

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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 (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

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.

–

BAUD

dev

–

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