Half-Duplex, iCoupler
Isolated RS-485 Transceiver
Data Sheet
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FEATURES
RS-485 transceiver with electrical data isolation
Complies with ANSI TIA/EIA-485-A and ISO 8482: 1987(E)
500 kbps data rate
Slew rate-limited driver outputs
Low power operation: 2.5 mA maximum
Suitable for 5 V or 3.3 V operations (V
DD1
)
High common-mode transient immunity: >25 kV/μs
True fail-safe receiver inputs
Chatter-free power-up/power-down protection
256 nodes on bus
Thermal shutdown protection
Safety and regulatory approvals
UL recognition: 2500 V rms for 1 minute per
UL 1577
VDE certificates of conformity
DIN V VDE V 0884-10 (VDE V 0884-10): 2006-12
V
IORM
= 560 V peak
Operating temperature range: −40°C to +85°C
APPLICATIONS
Low power RS-485/RS-422 networks
Isolated interfaces
Building control networks
Multipoint data transmission systems
FUNCTIONAL BLOCK DIAGRAM
ADM2481
DE
GALVANIC ISOLA
TION
TxD
RxD
A
B
RE
GND
1
GND
2
V
DD1
V
DD2
08920-001
Figure 1.
GENERAL DESCRIPTION
The ADM2481 differential bus transceiver is an integrated,
galvanically isolated component designed for bidirectional data
communication on balanced, multipoint bus transmission lines.
It complies with ANSI EIA/TIA-485-A and ISO 8482: 1987(E).
Using iCoupler® technology from Analog Devices, Inc., the
ADM2481 combines a 3-channel isolator, a three-state diffe-
rential line driver, and a differential input receiver into a single
package. The logic side of the device is powered with either a
5 V or 3 V supply, and the bus side uses a 5 V supply only.
The ADM2481 is slew-limited to reduce reflections with improp-
erly terminated transmission lines. The controlled slew rate
limits the data rate to 500 kbps. The input impedance of the
device is 96 kΩ, allowing up to 256 transceivers on the bus. Its
driver has an active-high enable feature. The driver differential
outputs and receiver differential inputs are connected internally
to form a differential I/O port. When the driver is disabled or
when V
DD1
or V
DD2
= 0 V, this imposes minimal loading on
the bus. An active-high receiver disable feature, which causes
the receiver output to enter a high impedance state, is provided
as well.
The receiver inputs have a true fail-safe feature that ensures a
logic-high receiver output level when the inputs are open or
shorted. This guarantees that the receiver outputs are in a
known state before communication begins and at the point
when communication ends.
Current limiting and thermal shutdown features protect against
output short circuits and bus contention situations that might
cause excessive power dissipation. The part is fully specified
over the industrial temperature range of −40°C to +85°C and is
available in a 16-lead, wide body SOIC package.
