LTC491IS#PBF Linear Technology, LTC491IS#PBF Datasheet - Page 7
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LTC491IS#PBF
Manufacturer Part Number
LTC491IS#PBF
Description
IC TXRX RS485 LOW POWER 14-SOIC
Manufacturer
Linear Technology
Type
Transceiverr
Datasheet
1.LTC491CNPBF.pdf
(12 pages)
Specifications of LTC491IS#PBF
Number Of Drivers/receivers
1/1
Protocol
RS422, RS485
Voltage - Supply
4.75 V ~ 5.25 V
Mounting Type
Surface Mount
Package / Case
14-SOIC (3.9mm Width), 14-SOL
Data Rate
2.5Mbps
Interface Circuit Standard 1
RS-422/RS-485
Number Of Receivers
1
Number Of Transmitters
1
Number Of Transceivers
1
Data Transmission Topology
Multidrop/Multipoint
Receiver Signal Type
Differential
Transmitter Signal Type
Differential
Single Supply Voltage (typ)
5V
Single Supply Voltage (min)
4.75V
Single Supply Voltage (max)
5.25V
Dual Supply Voltage (typ)
Not RequiredV
Dual Supply Voltage (min)
Not RequiredV
Dual Supply Voltage (max)
Not RequiredV
Supply Current
0.5mA
Power Supply Requirement
Single
Operating Temp Range
-40C to 85C
Operating Temperature Classification
Industrial
Mounting
Surface Mount
Pin Count
14
Package Type
SOIC N
No. Of Drivers
1
Supply Voltage Range
4.75V To 5.25V
Driver Case Style
SOIC
No. Of Pins
14
Operating Temperature Range
-40°C To +85°C
Msl
MSL 1 - Unlimited
Termination Type
SMD
Rohs Compliant
Yes
Filter Terminals
SMD
Ic Interface Type
RS422, RS485
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
APPLICATIO S I FOR ATIO
Typical Application
A typical connection of the LTC491 is shown in Figure 9.
Two twisted-pair wires connect up to 32 driver/receiver
pairs for full duplex data transmission. There are no
restrictions on where the chips are connected to the wires,
and it isn’t necessary to have the chips connected at the
ends. However, the wires must be terminated only at the
ends with a resistor equal to their characteristic imped-
ance, typically 120 . The input impedance of a receiver is
typically 20k
practice 50 to 60 transceivers can be connected to the
same wires. The optional shields around the twisted pair
help reduce unwanted noise, and are connected to GND at
one end.
The LTC491 can also be used as a line repeater as shown
in Figure 10. If the cable length is longer than 4000 feet, the
LTC491 is inserted in the middle of the cable with the
receiver output connected back to the driver input.
Thermal Shutdown
The LTC491 has a thermal shutdown feature which pro-
tects the part from excessive power dissipation. If the
RX
DX
2
3
4
5
to GND, or 0.6 unit RS-485 load, so in
DRIVER
U
RECEIVER
LTC491
U
12
11
10
9
W
120
120
LTC491
U
Figure 9. Typical Connection
DRIVER
9
DX
5
10
4
outputs of the driver are accidently shorted to a power
supply or low impedance source, up to 250mA can flow
through the part. The thermal shutdown circuit disables
the driver outputs when the internal temperature reaches
150 C and turns them back on when the temperature cools
to 130 C. If the outputs of two or more LTC491 drivers are
shorted directly, the driver outputs can not supply enough
current to activate the thermal shutdown. Thus, the ther-
mal shutdown circuit will not prevent contention faults
when two drivers are active on the bus at the same time.
RECEIVER
11
3 2
RX
DX
RX
12
2
3
4
5
LTC491 • F09
DRIVER
RECEIVER
LTC491
Figure 10. Line Repeater
120
120
12
11
10
9
12
11
10
9
LTC491 • F10
RECEIVER
120
120
LTC491
DRIVER
2
3
4
5
LTC491
DX
RX
DATA OUT
DATA IN
7
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