5 V Low Power
a
EIA RS-485 Transceiver
ADM1485
FEATURES
Meets EIA RS-485 Standard
30 Mbps Data Rate
FUNCTIONAL BLOCK DIAGRAM
8-Lead
Single 5 V Supply
–7 V to +12 V Bus Common-Mode Range
High Speed, Low Power BiCMOS
Thermal Shutdown Protection
Short-Circuit Protection
ADM1485
V
RO
R
CC
Driver Propagation Delay: 10 ns
Receiver Propagation Delay: 15 ns
High-Z Outputs with Power Off
Superior Upgrade for LTC1485
B
RE
DE
DI
A
APPLICATIONS
Low Power RS-485 Systems
DTE-DCE Interface
D
GND
Packet Switching
Local Area Networks
Data Concentration
Data Multiplexers
Integrated Services Digital Network (ISDN)
GENERAL DESCRIPTION
This minimizes the loading effect when the transceiver is not being
used. The high impedance driver output is maintained over the
entire common-mode voltage range from –7 V to +12 V.
The ADM1485 is a differential line transceiver suitable for high
speed bidirectional data communication on multipoint bus trans-
mission lines. It is designed for balanced data transmission and
complies with both RS-485 and RS-422 EIA Standards. The part
contains a differential line driver and a differential line receiver.
Both the driver and the receiver may be enabled independently.
When disabled, the outputs are three-stated.
The receiver contains a fail-safe feature that results in a logic
high output state if the inputs are unconnected (floating).
The ADM1485 is fabricated on BiCMOS, an advanced mixed
technology process combining low power CMOS with fast
switching bipolar technology. All inputs and outputs contain
protection against ESD; all driver outputs feature high source
and sink current capability. An epitaxial layer is used to guard
against latch-up.
The ADM1485 operates from a single 5 V power supply. Excessive
power dissipation caused by bus contention or by output shorting
is prevented by a thermal shutdown circuit. This feature forces
the driver output into a high impedance state if, during fault condi-
tions, a significant temperature increase is detected in the internal
driver circuitry.
The ADM1485 features extremely fast switching speeds. Minimal
driver propagation delays permit transmission at typical data rates
of 30 Mbps while low skew minimizes EMI interference.ꢀ
The part is fully specified over the commercial and industrial
temperature range and is available in PDIP, SOIC, and small
MSOP packages.
Up to 32 transceivers may be connected simultaneously on a bus,
but only one driver should be enabled at any time. It is important,
therefore, that the remaining disabled drivers do not load the bus.
To ensure this, the ADM1485 driver features high output
impedance when disabled and also when powered down.
'
REV.
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2012
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