ISL81485IU Intersil, ISL81485IU Datasheet - Page 6

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ISL81485IU

Manufacturer Part Number
ISL81485IU
Description
IC TXRX RS485/422 5V HS 8-MSOP
Manufacturer
Intersil
Type
Transceiverr
Datasheet

Specifications of ISL81485IU

Number Of Drivers/receivers
1/1
Protocol
RS422, RS485
Voltage - Supply
4.5 V ~ 5.5 V
Mounting Type
Surface Mount
Package / Case
8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
Test Circuits and Waveforms
Application Information
RS-485 and RS-422 are differential (balanced) data
transmission standards for use in long haul or noisy
environments. RS-422 is a subset of RS-485, so RS-485
transceivers are also RS-422 compliant. RS-422 is a point-
to-multipoint (multidrop) standard, which allows only one
driver and up to 10 (assuming one unit load devices)
receivers on each bus. RS-485 is a true multipoint standard,
which allows up to 32 one unit load devices (any
combination of drivers and receivers) on each bus. To allow
for multipoint operation, the RS-485 spec requires that
drivers must handle bus contention without sustaining any
damage.
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.
SIGNAL
GENERATOR
PARAMETER
t
t
t
t
HZ
ZH
LZ
ZL
SIGNAL
GENERATOR
+1.5V
FIGURE 5A. TEST CIRCUIT
FIGURE 6A. TEST CIRCUIT
RE
A
B
B
A
RE
DE
R
0
0
0
0
6
R
RO
RO
+1.5V
+1.5V
-1.5V
-1.5V
FIGURE 6. RECEIVER ENABLE AND DISABLE TIMES
A
(Continued)
15pF
FIGURE 5. RECEIVER PROPAGATION DELAY
1kΩ
15pF
SW
GND
GND
V
V
SW
CC
CC
GND
V
CC
ISL81485
Receiver Features
This device utilizes a differential input receiver for maximum
noise immunity and common mode rejection. Input sensitivity
is ±200mV, as required by the RS422 and RS-485
specifications.
Receiver input resistance surpasses the RS-422 spec of
4kΩ, and meets the RS-485 “Unit Load” requirement of 12kΩ
minimum, thereby allowing up to 32 devices on a bus.
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, or industrial
applications, where induced voltages are a definite concern.
The receiver includes a “fail-safe if open” function that
guarantees a high level receiver output if the receiver inputs
are unconnected (floating).
The receiver easily meets the data rate supported by the
driver, and receiver outputs are three-statable via the active
low RE input.
RO
A
RE
RO
RO
t
t
ZH
ZL
FIGURE 5B. MEASUREMENT POINTS
FIGURE 6B. MEASUREMENT POINTS
t
1.5V
PLH
1.5V
OUTPUT HIGH
50%
1.5V
1.5V
OUTPUT LOW
t
PHL
1.5V
t
t
HZ
1.5V
LZ
50%
V
V
OH
OL
- 0.5V
+ 0.5V
3V
0V
3V
0V
V
0V
V
V
V
CC
0V
OH
CC
OL

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