LT1039A Linear Technology, LT1039A Datasheet - Page 7

• Manufacturer Part Number: LT1039A
• Description: Triple RS232 Driver/Receiver with Shutdown
• Manufacturer: Linear Technology

APPLICATIONS
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
to V
output is in a high impedance state.
The receiver input impedance of the LT1039A is nominally
30k . For applications requiring a 5k input impedance,
a 5.6k resistor can be connected from the receiver input to
ground.
To protect against receiver input overloads in excess of
still maintain RS232 compatibility.
30V, a voltage clamp can be placed on the data line and
CC
ON/OFF
RS232
INPUT
INPUT
RS232
INPUT
to force a definite logic level when the receiver
RS232
INPUT
Driving CMOS Logic from a Receiver
5.6k
Input Overvoltage Protection
RECEIVER
1k
5k Impedance Matching
LT1039A
U
5.6k
INFORMATION
30V
*FORCES LOGIC INPUT STATE
30V
U
WHEN V
30k
ON/OFF
RECEIVER
51k*
W
IS LOW
30k
V
RECEIVER
CC
LOGIC
CMOS
LOGIC
OUTPUT
1039A AI08
LOGIC
OUTPUT
LOGIC
OUTPUT
U
1039A AI06
1039A AI07
Driver inputs should not be allowed to float. Any unused
inputs should be tied to V
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.
Keeping Alive One Receiver While in Shutdown
SHUTDOWN
RS232 Compatible Shutdown Control Line
RS232
RS232
INPUT
INPUT
LT1039A/LT1039A-16
2
3
2
3
BIAS
BIAS
LT1039A
LT1039A
CC
25k
25k
.
ON/OFF
ON/OFF
1039A AI07
1039A AI08
SHUTDOWN
17
16
17
16
LOGIC
INPUT
LOGIC
OUTPUT
7