ISL3178AEMBZ-T Intersil, ISL3178AEMBZ-T Datasheet - Page 8

• Manufacturer Part Number: ISL3178AEMBZ-T
• Description: TXRX ESD 3.3V RS485/422 8-SOIC
• Manufacturer: Intersil
• Type: Transceiverr

Specifications of ISL3178AEMBZ-T

• Number Of Drivers/receivers: 1/1
• Protocol: RS422, RS485
• Voltage - Supply: 3 V ~ 3.6 V
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS 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 long runs,
thus the wide CMR is necessary to handle ground potential
differences, as well as voltages induced in the cable by
external fields.
SIGNAL
GENERATOR
t
t
ZL(SHDN)
ZH(SHDN)
PARAMETER
t
t
ZH
ZL
(Note 6)
(Note 6)
SIGNAL
GENERATOR
t
t
HZ
LZ
(Note 11)
(Note 9)
GND
FIGURE 5A. TEST CIRCUIT
FIGURE 6A. TEST CIRCUIT
GND
RE
B
A
B
A
RE
R
DE
X
X
0
0
0
0
8
R
RO
RO
+1.5V
+1.5V
+1.5V
-1.5V
-1.5V
-1.5V
FIGURE 6. RECEIVER ENABLE AND DISABLE TIMES
A
15pF
(Continued)
FIGURE 5. RECEIVER PROPAGATION DELAY
1kΩ
15pF
SW
GND
GND
GND
V
V
V
SW
CC
CC
CC
GND
V
CC
ISL3178AE
Receiver Features
This device utilizes a differential input receiver for maximum
noise immunity and common mode rejection. Input sensitivity
is better than ±200mV, as required by the RS-422 and RS-485
specifications.
Receiver input resistance of 96kΩ surpasses the RS-422
spec of 4kΩ and is eight times the RS-485 “Unit Load (UL)”
requirement of 12kΩ 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 +9V/-7V outside the power supplies (i.e., +12V and -7V),
making them ideal for long networks where induced voltages
and ground potential differences are realistic concerns.
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. Fail-safe with shorted
inputs is achieved by setting the Rx upper switching point to
-50mV, thereby ensuring that the Rx sees 0V differential as a
high input level.
t
t
ZH
ZL
RO
A
RE
RO
RO
, t
, t
NOTE 9
NOTE 9
ZH(SHDN)
ZL(SHDN)
NOTE 9
FIGURE 5B. MEASUREMENT POINTS
FIGURE 6B. MEASUREMENT POINTS
t
PLH
0V
1.5V
OUTPUT HIGH
1.5V
1.5V
1.5V
OUTPUT LOW
t
PHL
t
t
0V
HZ
1.5V
LZ
1.5V
V
V
OH
OL
+1.5V
-1.5V
- 0.25V
+ 0.25V
3V
0V
May 6, 2009
V
0V
FN6887.1
CC
V
V
V
0V
OH
CC
OL