DETAILED DESCRIPTION
The SP1490E and SP1491E are full-duplex dif-
ferential 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 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.
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.
Receiver...
The receivers for both the SP1490E and
SP1491E have differential inputs with an input
sensitivity as low as ±200mV. Input impedance
of the receivers is typically 15KΩ (12KΩ mini-
mum). A wide common mode range of -7V to
+12V allows for large ground potential differ-
ences 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.
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 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
INPUTS
OUTPUTS
DE
DI
Y
Z
RE
SP1491E only
A-B
R
only
SP1491E
1
1
0
1
0
x
1
0
z
0
1
z
0
0
0
1
+0.2V
-0.2V
open
x
1
0
1
z
Transmit Function Truth Table
Recieve Function Truth Table
Date: 5/18/04
SP1490E/1491E Full Duplex RS-485 Transceivers
© Copyright 2004 Sipex Corporation
5
SIPEX [ SIPEX CORPORATION ]
