Final Electrical Specifications
LTC1535
Isolated RS485 Transceiver
August 1999
FEATURES
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DESCRIPTIO
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UL Rated Isolated RS485: 2500V
RMS
Half- or Full-Duplex
Eliminates Ground Loops
350kBd Maximum Data Rate
Self-Powered with 400kHz Converter
Fail-Safe Output High for Open or
Shorted Receiver Inputs
Short-Circuit Current Limit
Slow Slew Rate Control
68kΩ Input Impedance Allows Up to 128 Nodes
Thermal Shutdown
8kV ESD Protection On Driver Outputs and Receiver
Inputs
The LTC
®
1535 is an isolated RS485 full-duplex differential
line transceiver. Isolated RS485 is ideal for systems where
the ground loop is broken to allow for much larger com-
mon mode voltage ranges. An internal capacitive isolation
barrier provides 2500V
RMS
of isolation between the line
transceiver and the logic level interface. The powered side
contains a 400kHz push-pull converter to power the iso-
lated RS485 transceiver. Internal full-duplex communica-
tion occurs through the capacitive isolation barrier. The
transceiver meets RS485 and RS422 requirements.
The driver and receiver feature three-state outputs, with
the driver maintaining high impedance over the entire
common mode range. The drivers have short-circuit cur-
rent limits in both directions and a slow slew rate select to
minimize EMI or reflections. The 68kΩ receiver input
allows up to 128 node connections. A fail-safe feature
defaults to a high output state when the receiver inputs are
open or shorted.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
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Isolated RS485 Receiver/Driver
RS485 with Large Common Mode Voltage
Breaking RS485 Ground Loops
Multiple Unterminated Line Taps
TYPICAL APPLICATIO
**
CTX02-14659
1/2 BAT54C
+
10µF
2
1/2 BAT54C
2
V
CC
10µF
1
RO
28
RO
3
ST2
400kHz
2
11
GND2
14
V
CC2
+
1
V
CC
ST1
A
R
B
RO2
16
15
17
TWISTED-PAIR
CABLE
RE
DE
DI
27
26
25
4
1
RE
DE
DI
GND
D
Y
Z
SLO
13
12
18
1535 TA01
LOGIC COMMON
1
FLOATING RS485 COMMON
2
** TRANSFORMER
COILTRONICS (561) 241-7876
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
U
U
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1
LINER [ LINEAR TECHNOLOGY ]
