isl83086e-isl83088e Intersil Corporation, isl83086e-isl83088e Datasheet - Page 11

• Manufacturer Part Number: isl83086e-isl83088e
• Description: +-15kv Esd, 5v, Full Fail-safe, 1/8 Unit Load, Rs-485/rs-422 Transceivers
• Manufacturer: Intersil Corporation

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 specification 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.
Receiver Features
These devices utilize a differential input receiver for maximum
noise immunity and common mode rejection. Input sensitivity
is r200mV, as required by the RS-422 and RS-485
specifications.
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
SIGNAL
GENERATOR
t
t
ZH(SHDN)
ZL(SHDN)
PARAMETER
t
ISL83080E, ISL83082E, ISL83083E, ISL83084E, ISL83085E, ISL83086E, ISL83088E
t
ZH
ZL
(Note 9)
(Note 9)
t
t
HZ
LZ
(Note 11)
(Note 11)
GND
FIGURE 6A. TEST CIRCUIT
RE
FIGURE 6. RECEIVER ENABLE AND DISABLE TIMES (DOES NOT APPLY TO THE ISL83084E)
B
A
R
DE
0
0
0
0
0
0
11
RO
+1.5V
+1.5V
+1.5V
-1.5V
-1.5V
-1.5V
A
15pF
(Continued)
1k:
SW
GND
GND
GND
V
V
V
SW
CC
CC
CC
GND
V
CC
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 r7V 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
ISL83084E).
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.
t
t
ZH
NOTES 9, 11
ZL
NOTES 9, 11
RE
RO
RO
, t
, t
ZH(SHDN)
ZL(SHDN)
NOTE 9
FIGURE 6B. MEASUREMENT POINTS
1.5V
OUTPUT HIGH
1.5V
1.5V
OUTPUT LOW
t
t
HZ
1.5V
LZ
V
V
OH
OL
+ 0.5V
- 0.5V
February 27, 2008
3V
0V
FN6085.8
V
V
V
0V
OH
CC
OL