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PDF ADM3491-1 Data sheet ( Hoja de datos )
| Número de pieza | ADM3491-1 | |
| Descripción | EIA RS-485 Transceiver | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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Data Sheet
FEATURES
Operates with 3.3 V supply
EIA RS-422 and RS-485 compliant over full CM range
19 kΩ input impedance
Up to 50 transceivers on bus
20 Mbps data rate
Short-circuit protection
Specified over full temperature range
Thermal shutdown
Interoperable with 5 V logic
840 μA supply current
2 nA shutdown current
Available in PDIP, SOIC, and TSSOP
Meets IEC1000-4-4 (>1 kV)
8 ns skew
Upgrade for MAX3491, SN75ALS180
3.3 V, Full-Duplex, 840 μA,
20 Mbps, EIA RS-485 Transceiver
ADM3491-1
FUNCTIONAL BLOCK DIAGRAM
ADM3491-1
RO R
RE
A
B
DE
DI D
Z
Y
Figure 1.
APPLICATIONS
Telecommunications
DTE–DCE interface
Packet switching
Local area networks
Data concentration
Data multiplexers
Integrated services digital network (ISDN)
AppleTalk
Industrial controls
GENERAL DESCRIPTION
The ADM3491-1 is a low power, differential line transceiver
designed to operate using a single 3.3 V power supply. Low
power consumption, coupled with a shutdown mode, makes it
ideal for power-sensitive applications. It is suitable for commu-
nication on multipoint bus transmission lines.
The ADM3491-1 is intended for balanced data transmission
and complies with both Electronic Industries Association (EIA)
Standards RS-485 and RS-422. It contains a differential line
driver and a differential line receiver, making it suitable for full-
duplex data transfer.
The input impedance is 19 kΩ, allowing up to 50 transceivers to
be connected on the bus. A thermal shutdown circuit prevents
excessive power dissipation caused by bus contention or by
output shorting. This feature forces the driver output into a high
impedance state if a significant temperature increase is detected
in the internal driver circuitry during fault conditions.
If the inputs are unconnected (floating), the receiver contains a
fail-safe feature that results in a logic high output state.
The ADM3491-1 is fabricated on BiCMOS, an advanced mixed
technology process combining low power CMOS with fast
switching bipolar technology.
Rev. C
Document Feedback
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 that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700 ©1998–2014 Analog Devices, Inc. All rights reserved.
Technical Support
www.analog.com
1 page  
Data Sheet
ABSOLUTE MAXIMUM RATINGS
TA = 25°C, unless otherwise noted.
Table 4.
Parameter
VCC
Inputs
Driver Input (DI)
Control Inputs (DE, RE)
Receiver Inputs (A, B)
Outputs
Driver Outputs
Receiver Output
14-Lead PDIP, Power Dissipation
θJA, Thermal Impedance
14-Lead SOIC, Power Dissipation
θJA, Thermal Impedance
16-Lead TSSOP, Power Dissipation
θJA, Thermal Impedance
Operating Temperature Range
Industrial (A Version)
Storage Temperature Range
Lead Temperature (Soldering, 10 sec)
Vapor Phase (60 sec)
Infrared (15 sec)
ESD Rating
EFT Rating (IEC1000-4-4)
Rating
7V
−0.3 V to VCC + 0.3 V
−0.3 V to VCC + 0.3 V
−7.5 V to +12.5 V
−7.5 V to +12.5 V
−0.5 V to VCC + 0.5 V
800 mW
140°C/W
650 mW
115°C/W
500 mW
158°C/W
−40°C to +85°C
−65°C to +150°C
300°C
215°C
220°C
>2 kV
>1 kV
ADM3491-1
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
ESD CAUTION
Rev. C | Page 5 of 16
5 Page 
Data Sheet
THEORY OF OPERATION
DIFFERENTIAL DATA TRANSMISSION
Differential data transmission is used to reliably transmit data at
high rates over long distances and through noisy environments.
Differential transmission nullifies the effects of ground shifts and
noise signals that appear as common-mode voltages on the line.
The two main standards approved by the EIA specify the
electrical characteristics of transceivers used in differential
data transmission:
RS-422 standard specifies data rates up to 10 MBaud and
line lengths up to 4000 ft. A single driver can drive a
transmission line with up to 10 receivers.
RS-485 standard was defined to cater to true multipoint
communications. This standard meets or exceeds all the
requirements of RS-422, but also allows multiple drivers
and receivers to be connected to a single bus. An extended
common-mode range of −7 V to +12 V is defined.
The most significant differentiator of the RS-485 standard is
that the drivers can be disabled, thereby allowing more than one
to be connected to a single line. Only one driver should be
enabled at a time, but the RS-485 standard contains additional
specifications to guarantee device safety in the event of line
contention.
Table 6. Comparison of RS-422 and RS-485 Interface Standards
Specification
RS-422
RS-485
Transmission Type
Differential Differential
Maximum Cable Length
4000 ft.
4000 ft.
Minimum Driver Output Voltage ±2 V
±1.5 V
Driver Load Impedance
100 Ω
54 Ω
Receiver Input Resistance
4 kΩ min
12 kΩ min
Receiver Input Sensitivity
±200 mV
±200 mV
Receiver Input Voltage Range
−7 V to +7 V −7 V to +12 V
CABLE AND DATA RATE
The transmission line of choice for RS-485 communications is a
twisted pair. Twisted pair cable tends to cancel common-mode
noise and also causes cancellation of the magnetic fields gener-
ated by the current flowing through each wire, thereby reducing
the effective inductance of the pair.
The ADM3491-1 is designed for bidirectional data communica-
tions on multipoint transmission lines. A typical application
showing a multipoint transmission network is illustrated in
Figure 26. Only one driver can transmit at a particular time, but
multiple receivers can be enabled simultaneously.
ADM3491-1
As with any transmission line, it is important that reflections
be minimized. This can be achieved by terminating the extreme
ends of the line using resistors equal to the characteristic
impedance of the line. Stub lengths of the main line should
also be kept as short as possible. A properly terminated
transmission line appears purely resistive to the driver.
RECEIVER OPEN-CIRCUIT FAIL-SAFE FEATURE
The receiver input includes a fail-safe feature that guarantees a
logic high on the receiver when the inputs are open circuit or
floating.
3.3V
3.3V
0.1µF
0.1µF
RE VCC
RO
R
A
B
ADM3491-1
Z
DI
D
Y
DE
GND
RS-485/RS-422 LINK
VCC
DE
Y
DI
ZD
ADM3491-1
B
RO
AR
RE
GND
Figure 26. ADM3491-1 Full-Duplex Data Link
Table 7. Transmitting Truth Table
Inputs
Outputs
RE DE DI Z
Y
X1101
X1010
0 0 X Hi-Z Hi-Z
1 0 X Hi-Z Hi-Z
Table 8. Receiving Truth Table
Inputs
RE DE A–B
0 X ≥ +0.2 V
0 X ≤ −0.2 V
0 X Inputs O/C
1XX
Outputs
RO
0
0
1
Hi-Z
Rev. C | Page 11 of 16
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