SP491EEP-L Datasheet, PDF (7/12 Pages) Exar Corporation – Enhanced Full Duplex RS-485 Transceivers

DESCRIPTION
The SP490E and SP491E are
full-duplex differential transceiv-
ers 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 bi-
polar 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
receivers 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) com-
mon mode range to accommodate 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 SP490E and SP491E
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 SP491E has a driver enable
control line which is active high. A logic high
on DE (pin 4) of the SP491E will enable
the differential driver outputs. A logic low
on DE (pin 4) of the SP491E will tri-state the
driver outputs. The SP490E does not have
a driver enable.
Receiver...
The receivers for both the SP490E and
SP491E have differential inputs with an
input sensitivity 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 be-
tween systems. The receivers for both the
SP490E and SP491E 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.
The receiver of the SP491E has a receiver
enable control line which is active low. A logic
low on REB (pin 3) of the SP491E will enable
the differential receiver. A logic high on REB
(pin 3) of the SP491E will tri-state the re-
ceiver.
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • [phone] • www.exar.com

SP490E,491E_101_052413