LTC491
O U
W
U
PPLICATI
A
S I FOR ATIO
Typical Application
typically 20kΩ to GND, or 0.6 unit RS-485 load, so in
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.
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 120Ω. The input impedance of a receiver is
The LTC491 can also be used as a line repeater as shown
inFigure10.Ifthecablelengthislongerthan4000feet,the
LTC491 is inserted in the middle of the cable with the
receiver output connected back to the driver input.
12
12
2
3
2
3
120Ω
120Ω
120Ω
120Ω
RX
DX
RX
DX
RECEIVER
RECEIVER
11
11
4
4
10
9
10
9
5
5
DRIVER
DRIVER
LTC491
LTC491
9
10
11
12
RECEIVER
LTC491
DRIVER
5
4
3
2
LTC491 • TA10
DX
RX
Figure 9. Typical Connection
12
2
3
120Ω
RX
RECEIVER
11
DATA IN
4
10
5
120Ω
DATA OUT
DX
DRIVER
9
LTC491
LTC491 • TA11
Figure 10. Line Repeater
7
Linear [ Linear ]
