7

LTC1485

TI E WAVEFOR

S

G

WITCHI

S

Figure 9. Typical Connection

1.5V

0V

3V

1485 F08

1.5V

RO

RO

1.5V

0.5V

0.5V

OUTPUT NORMALLY LOW

OUTPUT NORMALLY HIGH

1.5V

0V

5V

RE

Figure 8. Receiver Enable and Disable Times

S

APPLICATI

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 120

Ω. 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.

6

7

120

Ω

120

Ω

3

4

RX

DX

2

1

1485 F09

LTC1485

RX

DX

4

1

3

2

LTC1485

RECEIVER

RX

DX

7

4

1

3

2

LTC1485

6

RECEIVER

DRIVER

RECEIVER

DRIVER

DRIVER