7
LT1039/LT1039-16
1039fd
APPLICATIONS INFORMATION
WUU
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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
CC
to force a definite logic level when the receiver
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
WHEN V
ON/OFF
IS LOW
51k*
V
CC
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
inputs should be tied to V
CC
.
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
30kΩ. For applications requiring a 5kΩ input impedance,
a 5.6k resistor can be connected from the receiver input to
ground.
5kΩ Impedance Matching
1039 AI08
RS232
INPUT
LOGIC
OUTPUT
RECEIVER
30k
5.6k
