Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com

SP3080E-SP3088E_100_062309

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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 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.

The SP3082E, SP3085E and SP3088E are

half-duplex transceivers, while the SP3080E,

SP3081E, SP3083E, SP3084E, SP3086E, and

SP3087E are full duplex transceivers.

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.

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.

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.

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 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.

±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.

ESD protection can be tested in various ways.

The transmitter outputs and receiver inputs of