SP490_05 Datasheet, PDF (7/12 Pages) Sipex Corporation – Full Duplex RS-485 Transceivers

DESCRIPTION
The SP490 and SP491 are full-duplex differential
transceivers that meet the requirements of
RS-485 and RS-422. Fabricated with a Sipex
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 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) common 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 SP490 and SP491 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 SP491 has a driver enable
control line which is active high. A logic high
on DE (pin 4) of the SP491 will enable
the differential driver outputs. A logic low
on DE (pin 4) of the SP491 will tri-state the
driver outputs. The SP490 does not have a
driver enable.
Receiver...
The receivers for both the SP490 and SP491
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
between systems. The receivers for both the
SP490 and SP491 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 SP491 has a receiver
enable control line which is active low. A logic
low on REB (pin 3) of the SP491 will enable
the differential receiver. A logic high on REB
(pin 3) of the SP491 will tri-state the receiver.
Date: 02/24/05
SP490/491 Full Duplex RS-485 Transceivers
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