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ISL83080E Datasheet(PDF) 12 Page - Renesas Technology Corp

Part No. ISL83080E
Description  Â±15kV ESD, 5V, Full Fail-Safe, 1/8 Unit Load, RS-485/RS-422 Transceivers
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Manufacturer  RENESAS [Renesas Technology Corp]
Direct Link  http://www.renesas.com
Logo RENESAS - Renesas Technology Corp

ISL83080E Datasheet(HTML) 12 Page - Renesas Technology Corp

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FN6085 Rev 10.00
Page 12 of 21
February 15, 2016
Another important advantage of RS-485 is the extended
common mode range (CMR), which specifies that the driver
outputs and receiver inputs withstand signals that range from
+12V to -7V. RS-422 and RS-485 are intended for runs as
long as 4000’, so the wide CMR is necessary to handle
ground potential differences, as well as voltages induced in
the cable by external fields.
Receiver Features
These devices utilize a differential input receiver for maximum
noise immunity and common mode rejection. Input sensitivity
is ±200mV, as required by the RS-422 and RS-485
Receiver input resistance of 96k
 surpasses the RS-422
specification of 4k
, and is eight times the RS-485 “Unit
Load (UL)” requirement of 12k
 minimum. Thus, these
products are known as “one-eighth UL” transceivers, and
there can be up to 256 of these devices on a network while
still complying with the RS-485 loading specification.
Receiver inputs function with common mode voltages as
great as ±7V outside the power supplies (i.e., +12V and
-7V), making them ideal for long networks where induced
voltages are a realistic concern.
All the receivers include a “full fail-safe” function that
guarantees a high level receiver output if the receiver inputs
are unconnected (floating) or shorted.
Receivers easily meet the data rates supported by the
corresponding driver, and all receiver outputs are
three-statable via the active low RE input (except for the
Driver Features
The RS-485/RS-422 driver is a differential output device that
delivers at least 1.5V across a 54
 load (RS-485), and at
least 2V across a 100
 load (RS-422). The drivers feature
low propagation delay skew to maximize bit width, and to
minimize EMI.
All drivers are three-statable via the active high DE input
(except for the ISL83084E).
The 115kbps and 500kbps driver outputs are slew rate
limited to minimize EMI, and to minimize reflections in
unterminated or improperly terminated networks. Outputs of
the ISL83086E, ISL83088E drivers are not limited, so faster
output transition times allow data rates of at least 10Mbps.
Hot Plug Function
When a piece of equipment powers up, there is a period of
time where the processor or ASIC driving the RS-485 control
lines (DE, RE) is unable to ensure that the RS-485 Tx and
Rx outputs are kept disabled. If the equipment is connected
to the bus, a driver activating prematurely during power-up
may crash the bus. To avoid this scenario, the ISL83080,
ISL83082, ISL83083, ISL83085 versions incorporate a “Hot
Plug” function. Circuitry monitoring VCC ensures that, during
power-up and power-down, the Tx and Rx outputs remain
disabled, regardless of the state of DE and RE, if VCC is less
than ~3.4V. This gives the processor/ASIC a chance to stabilize
and drive the RS-485 control lines to the proper states.
ESD Protection
All pins on these devices include class 3 Human Body
Model (HBM) ESD protection structures, but the RS-485
pins (driver outputs and receiver inputs) incorporate
advanced structures allowing them to survive ESD events
in excess of ±15kV HBM. The RS-485 pins are particularly
vulnerable to ESD damage because they typically connect
to an exposed port on the exterior of the finished product.
Simply touching the port pins, or connecting a cable, can
cause an ESD event that might destroy unprotected ICs.
These new ESD structures protect the device whether or
not it is powered up, protect without allowing any latchup
mechanism to activate, and without degrading the RS-485
common mode range of -7V to +12V. This built-in ESD
protection eliminates the need for board level protection
structures (e.g., transient suppression diodes), and the
associated, undesirable capacitive load they present.
Data Rate, Cables, and Terminations
RS-485/RS-422 are intended for network lengths up to
4000’, but the maximum system data rate decreases as the
transmission length increases. Devices operating at 10Mbps
are limited to lengths less than 100’, while the 115kbps
versions can operate at full data rates with lengths of several
Twisted pair is the cable of choice for RS-485/RS-422
networks. Twisted pair cables tend to pick up noise and
other electromagnetically induced voltages as common
mode signals, which are effectively rejected by the
differential receivers in these ICs.
Proper termination is imperative (when using the 10Mbps
devices) to minimize reflections. Short networks using the
TIME (40µs/DIV)
RL = 1k
RL = 1k

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