SP490E Datasheet, PDF (7/12 Pages) Sipex Corporation – Enhanced Full Duplex RS-485 Transceivers

FEATURES
The SP490E and SP491E 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.
THEORY OF OPERATION
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.
Drivers
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.
Receivers
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
between 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 receiver.
ESD Tolerance
The SP490E/SP491E devices incorporate
ruggedized ESD cells on all driver output
and receiver input pins. The ESD structure is
improved over our previous family for more
rugged applications and environments sensitive
to electro-static discharges and associated
transients. The improved ESD tolerance is at
least ±15kV without damage nor latch-up.
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 differ-
ential 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.
R_CC
R_SS
DC Power
Source
SW1
C_SS
SW2
Device
Under
Test
Figure 9. ESD Test Circuit for Human Body Model
SP490EDS/14
SP490E Enhanced Full Duplex RS-485 Transceivers
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