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Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 50-668-707 • www.exar.com

SP3490_349_02_0270

The

SP3490 and SP3491 are two members

in the family of +3.3V low power full-du-

plex transceivers that meet the electrical

specifications of the RS-485 and RS-422

serial protocols. These devices are pin-to-

pin compatible with the

Exar SP490 and

SP49 devices as well as popular industry

standards.The

SP3490andSP3491feature

Exar'sBiCMOSprocessallowinglowpower

operation without sacrificing performance.

The RS-485 standard is ideal for multi-drop

applicationsandforlong-distanceinterfaces.

RS-485allowsupto32driversand32receiv-

ers to be connected to a data bus, making it

an ideal choice for multi-drop applications.

Since the cabling can be as long as 4,000

feet, RS-485 transceivers are equipped with

a wide (-7V to +2V) common mode range

to accommodate ground potential differ-

ences. Because RS-485 is a differential

interface, data is virtually immune to noise

in the transmission line.

Drivers

Thedriversforboththe

SP3490andSP3491

have differential outputs. The typical voltage

outputswingwithnoloadwillbe0voltstoVcc.

With worst case loading of 54Ω across the

differential outputs, the drivers can maintain

greater than .5V voltage levels.

The driver of the

SP3491 has a driver en-

able control line which is active HIGH. A

logic HIGH on DE (pin 4) of the

SP3491

will enable the differential driver outputs. A

logic LOW on the DE(pin 4) will tri-state the

driver outputs. The

SP3490 does not have

a driver enable.

Receivers

The receivers of the

SP3490 and SP3491

have differential inputs with an input sensi-

tivity of ±200mV. Input impedance of the

receivers is typically 15kΩ (12kΩ minimum).

A wide common mode range of -7V to +2V

allows for large ground potential differences

betweensystems. The receiversforboththe

SP3490 and SP3491 are equipped with a

fail-safe feature that guarantees the receiver

output will be in a HIGH state when the input

is left unconnected.

The receiver of the

SP3491 has a enable

control line which is active LOW. A logic

LOW on REB (pin 3) of the

SP3491 will en-

able the differential receiver. A logic HIGH

on REB (pin 3) of the

SP3491 will tri-state

the receiver.

DESCRIPTION