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Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com

SP1490_SP1491E_100_061209

The SP1490E and SP1491E are full-duplex dif-

ferential transceivers that meet the requirements

of RS-485 and RS-422. Fabricated with a Exar

proprietary BiCMOS process, both products

require a fraction of the power of older bipolar

designs.

The RS-485 standard is ideal for multi-drop

applications or for long-distance interfaces.

RS-485 allows up to 32 drivers and 32 receiv-

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 +12V) common mode range to accom-

modate ground potential differences. Because

RS-485 is a differential interface, data is virtually

immune to noise in the transmission line.

driver...

The drivers for both the SP1490E and SP1491E

have differential outputs. The typical voltage

output swing with no load will be 0 volts to +5

volts. With worst case loading of 54Ω across

the differential outputs, the driver can maintain

greater than 1.5V voltage levels.

The driver of the SP1491E has a driver enable

control line which is active high. A logic high

on DE (pin 4) of the SP1491E will enable

the differential driver outputs.

A logic low on DE (pin 4) of the SP1491E will

tri-state the driver outputs. The SP1490E does

not have a driver enable.

receiver...

ThereceiversforboththeSP1490EandSP1491E

have differential inputs with an input sensitiv-

ity as low as ±200mV. Input impedance of the

receivers is typically 15KΩ (12KΩ minimum).

A wide common mode range of -7V to +12V

allows for large ground potential differences

between systems. The receivers for both the

SP1490E and SP1491E are equipped with

the fail-safe feature. Fail-safe guarantees that

the receiver output will be in a high state when

the input is left unconnected and floating.

The receiver of the SP1491E has a receiver

enable control line which is active low. A logic

low on REB (pin 3) of the SP1491E will enable

the differential receiver. A logic high on REB

(pin 3) of the SP1491E will tri-state the re-

ceiver.

INPUTS

OUTPUTS

DE

SP1491E only

DI

Y

Z

1

1

0

1

0

x

1

0

z

0

1

z

INPUTS

OUTPUTS

RE

SP1491E

A-B

R

0

0

0

1

+0.2V

-0.2V

open

x

1

0

1

z

Transmit Function Truth Table

Recieve Function Truth Table

only

dEtaiLEd dEScriPtion