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PDF ADM3493 Data sheet ( Hoja de datos )
| Número de pieza | ADM3493 | |
| Descripción | Half Duplex RS-485/RS-422 Transceiver | |
| Fabricantes | Analog Devices | |
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3.3 V Slew Rate Limited,
Half Duplex RS-485/RS-422 Transceiver
ADM3493
FEATURES
Operates with 3.3 V supply
Interoperable with 5 V logic
EIA RS-422 and RS-485 compliant over full CM range
Data rate: 250 kbps
Half duplex transceiver
Reduced slew rates for low EMI
2 nA supply current in shutdown mode
Up to 256 transceivers on a bus
−7 V to +12 V bus common-mode range
Specified over −40°C to +85°C temperature range
8 ns skew
Available in 8-lead SOIC
APPLICATIONS
Low power RS-485 applications
EMI sensitive systems
DTE-DCE interfaces
Industrial control
Packet switching
Local area networks
Level translators
FUNCTIONAL BLOCK DIAGRAM
VCC
ADM3493
RO R
RE
DE
DI D
A
B
GND
Figure 1.
GENERAL DESCRIPTION
The ADM3493 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. The ADM3493 is suitable
for communication on multipoint bus transmission lines.
The device contains one driver and one receiver. Designed for
half-duplex communication, the ADM3493 features a slew rate
limited driver that minimizes EMI and reduces reflections
caused by improperly terminated cables, allowing error-free
data transmission at data rates up to 250 kbps.
The receiver input impedance is 96 kΩ, allowing up to 256
transceivers to be connected on the bus. A thermal shutdown
circuit prevents excessive power dissipation caused by bus
contention or by output shorting. If a significant temperature
increase is detected in the internal driver circuitry during fault
conditions then the thermal shutdown circuit forces the driver
output into a high impedance state. The receiver contains a fail-
safe feature that results in a logic high output state, if the inputs
are unconnected (floating).
The ADM3493 is fully specified over the commercial and
industrial temperature ranges and is available in an 8-lead SOIC.
Rev. 0
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
www.analog.com
Fax: 781.461.3113
©2005 Analog Devices, Inc. All rights reserved.
1 page  
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ABSOLUTE MAXIMUM RATINGS
TA = 25°C, unless otherwise noted.
Table 3.
Parameter
VCC to GND
Digital I/O Voltage (DE, RE, DI)
Digital I/O Voltage (ROUT)
Driver Output/Receiver Input Voltage
Operating Temperature Range
Storage Temperature Range
θJA Thermal Impedance
8-Lead SOIC
Lead Temperature
Soldering (10 seconds)
Vapor Phase (60 seconds)
Infrared (15 seconds)
Rating
7V
−0.3 V to VCC + 0.3 V
VCC − 0.5 V to VCC + 0.5 V
−7.5 V to +12.5 V
−40°C to +85°C
−65°C to +125°C
121°C/W
300°C
215°C
220°C
ADM3493
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
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on
the human body and test equipment and can discharge without detection. Although this product features
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance
degradation or loss of functionality.
Rev. 0 | Page 5 of 12
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ADM3493
CIRCUIT DESCRIPTION
The ADM3493 is a low power transceiver for RS-485 and
RS-422 communications. The ADM3493 can transmit and
receive at data rates up to 250 kbps in a half duplex
configuration. Driver Enable (DE) and Receiver Enable (RE)
pins are included when disabled; the driver and receiver
outputs are high impedance.
Table 5. Transmitting Truth Table
Transmitting Inputs
Transmitting
Outputs
RE DE DI B A
X1 1 1 0 1
X1 1 0 1 0
0 0 X1 High-Z2 High-Z2
1 0 X1 High-Z2 High-Z2
Mode
Normal
Normal
Normal
Shutdown
1 X = Don’t care.
2 High-Z = High Impedance.
Table 6. Receiving Truth Table
Receiving Inputs
RE DE
A-B
0 0 ≥+0.2 V
0 0 ≤−0.2 V
0 0 Inputs Open
10
X1
1 X = Don’t care.
2 High-Z = High Impedance
Receiving
Outputs
RO
1
0
1
High-Z2
Mode
Normal
Normal
Normal
Shutdown
REDUCED EMI AND REFLECTIONS
The ADM3493 is a slew rate limited transceiver, minimizing
EMI and reducing reflections caused by improperly terminated
cables.
LOW POWER SHUTDOWN MODE
A low power shutdown mode is initiated by bringing both RE
high and DE low. The ADM3493 does not shut down unless
both the driver and receiver are disabled (high impedance). In
shutdown, the ADM3493 typically draws only 2 nA of supply
current. For the ADM3493, the tPSH and tPSL enable times assume
the part was in the low power shutdown mode; the tPZH and tPZL
enable times assume the receiver or driver was disabled, but the
part was not shut down.
DRIVER OUTPUT PROTECTION
Two methods are implemented to prevent excessive output
current and power dissipation caused by faults or by bus
contention. Current limit protection on the output stage
provides immediate protection against short circuits over the
whole common-mode voltage range (see Typical Performance
Characteristics). In addition, a thermal shutdown circuit forces
the driver outputs into a high impedance state if the die
temperature rises excessively.
PROPAGATION DELAY
Skew time is simply the difference between the low-to-high and
high-to-low propagation delay. Small driver/receiver skew times
help maintain a symmetrical mark-space ratio (50% duty cycle).
The receiver skew time, |tPRLH - tPRHL|, is 20 ns for the ADM3493.
The driver skew time is typically under 100 ns.
TYPICAL APPLICATIONS
The ADM3493 transceiver is designed for bidirectional data
communications on multipoint bus transmission lines. Figure
22 shows a typical network application’s circuits. To minimize
reflections, the line should be terminated at both ends in its
characteristic impedance, and stub lengths off the main line
should be kept as short as possible. The slew rate limited
ADM3493 is tolerant of imperfect termination.
ADM3493
VCC
MAXIMUM NUMBER OF TRANSCEIVERS ON BUS = 256
ADM3493
RO R
RE
DE
DI D
A R1
RT
B
R2
A
ADM3493
B
A
RT
B
AB
ADM3493
R RO
RE
DE
D DI
R
D
R
D
RO RE DE DI
RO RE DE DI
NOTES
1. RT IS EQUAL TO THE CHARACTERISTIC IMPEDANCE OF THE CABLE.
Figure 28. ADM3493 Typical Half Duplex RS-485 Network
Rev. 0 | Page 11 of 12
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| PDF Descargar | [ Datasheet ADM3493.PDF ] | |
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