DESCRIPTION
DETAILED DESCRIPTION
SP3080E-SP3088E is a family of advanced
RS-485/RS-422 transceivers. Each contains
one driver and one receiver. These devices
feature fail-safe circuitry that guarantees a
logic-high receiver output when the receiver
inputs are open or shorted, or when they are
connected to a terminated transmission line
with all drivers disabled. SP3080E, SP3082E,
SP3083E, SP3085E, SP3086E and SP3088E
also feature a hot-swap capability allowing live
insertion without error data transfer.
The receiver thresholds of the SP3080E family,
are very precise and offset by at least a 40mV
noise margin from ground. This results in a
logic-high receiver output at zero volts input dif-
ferential while maintaining compliance with the
EIA/TIA-485 standard of ±200mV.
HOT-SWAP CAPABILITY
When a micro-processor or other logic device
undergoes its power-up sequence its logic-
outputs are typically at high impedance. In this
state they are unable to drive the DE and sig-
nals to a defined logic level. During this period,
noise, parasitic coupling or leakage from other
devices could cause standard CMOS enable in-
puts to drift to an incorrect logic level.
The SP3080E, SP3081E and SP3082E fea-
ture reduced slew-rate drivers that minimize
EMI and reduce reflections caused by improp-
erly terminated cables, allowing error-free data
transmission up to 115kbps. The SP3083E,
SP3084E and SP3085E also offer slew-rate
limits allowing transmit speeds up to 500kbps.
The SP3086E, SP3087E, SP3088E driver slew
rates are not limited, making transmit speeds
up to 20Mbps possible.
If circuit boards are inserted into an energized
backplane (commonly called “live insertion” or
“hot-swap”) power may be suddenly applied to
all circuits. Without the hot-swap capability, this
situation could improperly enable the transceiv-
er’s driver or receiver, driving invalid data onto
shared busses and possibly causing driver con-
tention or device damage.
The SP3082E, SP3085E and SP3088E are
half-duplex transceivers, while the SP3080E,
SP3081E, SP3083E, SP3084E, SP3086E, and
SP3087E are full duplex transceivers.
The SP3080E family contains a special power-
on-reset circuit that holds DE low and RE high
for approximately 10 microseconds. After this
initial power-up sequence the hot-swap circuit
becomes transparent, allowing for normal, un-
skewed enable and disable timings.
All devices operate from a single 5.0V supply.
Drivers are output short-circuit current limited.
Thermal-shutdown circuitry protects drivers
against excessive power dissipation. When ac-
tivated, the thermal-shutdown circuitry places
the driver outputs into a high-impedance state.
±15KV ESD PROTECTION
ESD-protection structures are incorporated
on all pins to protect against electrostatic dis-
charges encountered during handling and as-
sembly. The driver output and receiver inputs
of the SP3080E family have extra protection
against static electricity. Exar uses state of the
art structures to protect these pins against ESD
of ±15kV without damage. The ESD structures
withstand high ESD in all states: normal opera-
tion, shutdown, and powered down. After an
ESD event, the SP3080E - SP3088E keeps
working without latch-up or damage.
RECEIVER INPUT FILTERING
SP3080E-SP3085E receivers incorporate input
filtering in addition to input hysteresis. This fil-
tering enhances noise immunity with differential
signals that have very slow rise and fall times.
Receiver propagation delay increases due to
this filtering.
ADVANCED FAIL SAFE
Ordinary RS485 differential receivers will be in
an indeterminate state whenever A - B is less
than ±200mV. This situation can occur when-
ever the data bus is not being actively driven.
The Advanced Failsafe feature of the SP3080E
family guarantees a logic-high receiver output
if the receiver’s differential inputs are shorted,
open-circuit, or if they are shunted by a termi-
nation resistor.
ESD protection can be tested in various ways.
The transmitter outputs and receiver inputs of
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com
SP3080E-SP3088E_100_062309
20
EXAR [ EXAR CORPORATION ]
