SP1486E Datasheet, PDF (12/15 Pages) Sipex Corporation – +5V, 20Mbps PROFIBUS RS485/RS422 Transceivers Advanced Failsafe, 1/8th Unit Load, ±15kV ESD-Protected

DETAILED DESCRIPTION
SP1486E is an advanced RS485/RS422 trans-
ceiver, ideal for PROFIBUS applications. Each
device contains one high speed driver and re-
ceiver capable of speeds up to 20Mbps with
low skew.
The device is designed for reliability in demand-
ing operating conditions. It features a 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 termi-
nated transmission line with all drivers disabled.
Control inputs (DE and RE) also feature a hot-
swap capability allowing live insertion without
error data transfer.
The device operates 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.
PROFIBUS (EN50170 or DIN19245)
The PROFIBUS standard originated in Europe
but has spread worldwide as an industrial field-
bus for use in process automation and factory
control. There are a number of different imple-
mentations, but one of the most widely used is
PROFIBUS-DP (Process Field Bus - Distribut-
ed Peripherals). DP uses RS485 as its physical
layer along with a proprietary data-link layer.
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 SP1486E
guarantees a logic-high receiver output if the
receiver’s differential inputs are shorted, open-
circuit, or if they are shunted by a termination
resistor.
The receiver thresholds of the SP1486E 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 differential
while maintaining compliance with the EIA/TIA-
485 standard of ±200mV.
DESCRIPTION
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 RE
signals to a defined logic level. During this pe-
riod, noise, parasitic coupling or leakage from
other devices could cause standard CMOS en-
able inputs 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 trans-
ceiver’s driver or receiver, driving invalid data
onto shared busses and possibly causing driver
contention or device damage.
The SP1486E 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 discharg-
es encountered during handling and assem-
bly. The driver output and receiver inputs 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 operation, shutdown, and pow-
ered down. After an ESD event, the SP1486E
keeps working without latch-up or damage.
ESD protection can be tested in various ways.
The transmitter outputs and receiver inputs of
the SP1486E are characterized for protection to
the following limits
• ±15kV using the Human Body Model
• ±8kV using the Contact Discharge method
specified in IEC 1000-4-2
• ±15kV Air-gap
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com
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