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LT1485

Differential Bus Transceiver

Linear Technology 

SWITCHI G TI E WAVEFOR S

3V

RE

0V

5V

RO

VOL

1.5V

f = 1MHz; tr ≤ 10ns; tf ≤ 10ns

tZL

1.5V OUTPUT NORMALLY LOW

1.5V

tLZ

0.5V

VOH

RO

0V

1.5V

tZH

OUTPUT NORMALLY HIGH

0.5V

tHZ

1485 F08

Figure 8. Receiver Enable and Disable Times

LTC1485

APPLICATI S I FOR ATIO

Typical Application

A typical connection of the LTC1485 is shown in Figure 9.

Two twisted pair wires connect up to 32 driver/receiver

pairs for half 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

typically 20k to GND, or 0.6 unit RS485 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.

LTC1485

RX 1

2

3

RECEIVER

DX 4

DRIVER

7

120Ω

8

120Ω

LTC1485

RECEIVER

1 RX

2

3

DRIVER

4 DX

LTC1485

RECEIVER

1 RX

2

3

7

DRIVER

4 DX

8

1485 F09

Figure 9. Typical Connection

7

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