a
FEATURES
Meets EIA RS-485 Standard
30 Mb/s Data Rate
Single +5 V Supply
–7 V to +12 V Bus Common-Mode Range
High Speed, Low Power BiCMOS
Thermal Shutdown Protection
Short Circuit Protection
Zero Skew Driver
Driver Propagation Delay: 10 ns
Receiver Propagation Delay: 25 ns
High Z Outputs with Power Off
Superior Upgrade for LTC1485
APPLICATIONS
Low Power RS-485 Systems
DTE-DCE Interface
Packet Switching
Local Area Networks
Data Concentration
Data Multiplexers
Integrated Services Digital Network (ISDN)
+5 V Low Power
EIA RS-485 Transceiver
ADM1485
FUNCTIONAL BLOCK DIAGRAM
8-Lead
ADM1485
RO
R
V
CC
RE
B
DE
A
DI
D
GND
GENERAL DESCRIPTION
The ADM1485 is a differential line transceiver suitable for high
speed bidirectional data communication on multipoint bus
transmission lines. It is designed for balanced data transmission
and complies with both EIA Standards RS-485 and RS-422.
The part contains a differential line driver and a differential line
receiver. Both the driver and the receiver may be enabled inde-
pendently. When disabled, the outputs are tristated.
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 conditions a significant temperature increase is
detected in the internal driver circuitry.
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.
This minimizes the loading effect when the transceiver is not
being utilized. The high impedance driver output is maintained
over the entire common-mode voltage range from –7 V to +12 V.
The receiver contains a fail safe feature which 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 features extremely fast switching speeds. Mini-
mal driver propagation delays permit transmission at data rates
up to 30 Mbits/s while low skew minimizes EMI interference.
The part is fully specified over the commercial and industrial
temperature range and is available in an 8-lead DIL/SOIC
package.
REV. A
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 2000
AD [ ANALOG DEVICES ]
