SP3490 Datasheet, PDF (9/12 Pages) Sipex Corporation – +3.3V Low Power Full Duplex RS-485 Transceivers with 10Mbps Data Rate

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
SP491 devices as well as popular industry
standards. The SP3490 and SP3491 feature
Exar's BiCMOS process allowing low power
operation without sacrificing performance.
The RS-485 standard is ideal for multi-drop
applications and 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 accommodate ground potential differ-
ences. Because RS-485 is a differential
interface, data is virtually immune to noise
in the transmission line.
Drivers
The drivers for both the SP3490 and SP3491
have differential outputs. The typical voltage
output swing with no load will be 0 volts to Vcc.
With worst case loading of 54Ω across the
differential outputs, the drivers can maintain
greater than 1.5V 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
DESCRIPTION
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 +12V
allows for large ground potential differences
between systems. The receivers for both the
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.
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com

SP3490_3491_102_102710