Datasheet

LT1039A/LT1039A-16
7
1039afb
For more information www.linear.com/1039
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.
applicaTions inForMaTion
Driving CMOS Logic from a Receiver
Input Overvoltage Protection
5kΩ Impedance Matching
Keeping Alive One Receiver While in Shutdown
RS232 Compatible Shutdown Control Line
LT1039A
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
RS232
INPUT
LOGIC
OUTPUT
RECEIVER
1039A AI07
30k
1k
30V
30V
5.6k
1039A AI08
RS232
INPUT
LOGIC
OUTPUT
RECEIVER
30k
5.6k
LT1039A
25k
LOGIC
SHUTDOWN
INPUT
2
3 16
17
BIAS
RS232
INPUT
ON/OFF
LOGIC
OUTPUT
1039A AI09
LT1039A
25k
2
3 16
17
BIAS
RS232
SHUTDOWN
INPUT
ON/OFF
1039A AI10
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.
The receiver input impedance of the LT1039A is nominally
30kΩ. For applications requiring a 5kΩ input impedance,
a 5.6k resistor can be connected from the receiver input
to ground.
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.