7

LT1039/LT1039-16

1039fd

When driving CMOS logic from a receiver that will be used

in the shutdown mode and there is no other active receiver

on the line, a 51k resistor can be placed from the logic input

output is in a high impedance state.

Keeping Alive One Receiver While in Shutdown

LT1039

25k

LOGIC

SHUTDOWN

INPUT

2

3

16

17

BIAS

RS232

INPUT

ON/OFF

LOGIC

OUTPUT

1039 AI09

RS232 Compatible Shutdown Control Line

LT1039

25k

2

316

17

BIAS

RS232

SHUTDOWN

INPUT

ON/OFF

1039A AI10

Driving CMOS Logic from a Receiver

LT1039

RECEIVER

RS232

INPUT

ON/OFF

INPUT

LOGIC

OUTPUT

*FORCES LOGIC INPUT STATE

51k*

1039A AI06

CMOS

LOGIC

To protect against receiver input overloads in excess of

±30V, a voltage clamp can be placed on the data line and

still maintain RS232 compatibility.

Input Overvoltage Protection

RS232

INPUT

LOGIC

OUTPUT

RECEIVER

1039 AI07

30k

1k

30V

30V

5.6k

Driver inputs should not be allowed to float. Any unused

The BIAS pin is used to “keep alive” one receiver while in

the shutdown mode (all other circuitry being inactive).

This allows a system to be in shutdown and still have one

active receiver for transferring data.

It can also be used to make an RS232 compatible shut-

down control line. Driving the BIAS pin low through a

resistance of 24k to 30k keeps the receiver active. Do not

drive the BIAS pin directly from a logic output without the

series resistor. An unused BIAS pin should be left open.

The receiver input impedance of the LT1039 is nominally

30k

Ω. For applications requiring a 5kΩ input impedance,

a 5.6k resistor can be connected from the receiver input to

ground.

5k

Ω Impedance Matching

1039 AI08

RS232

INPUT

LOGIC

OUTPUT

RECEIVER

30k

5.6k