LT1080/LT1081
APPLICATIO S I FOR ATIO
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.
V
CC
LT1080
RECEIVER
51k*
RS232
INPUT
CMOS
LOGIC
LOGIC
OUTPUT
ON/OFF
INPUT
* FORCES LOGIC INPUT STATE WHEN V
ON/OFF
IS LOW
1080/81 F06
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.
RS232
INPUT
1k*
RECEIVER
30V
30V
5k
LOGIC
OUTPUT
* A PTC THERMISTOR WILL ALLOW
CONTINUOUS OVERLOAD OF GREATER THAN
±100V
1080/81 F067
TYPICAL APPLICATIO
12V INPUT*
1µF
12
LOGIC
INPUTS
11
13
LOGIC
OUTPUTS
10
18
ON/OFF
* PIN 1 USED ON LT1081.
U
The generated driver supplies (V
+
and V
–
) may be used to
power external circuitry such as other RS232 drivers or op
amps. They should be loaded with care, since excessive
loading can cause the generated supply voltages to drop,
causing the RS232 driver output voltages to fall below
RS232 requirements. See the graph “Supply Generator
Outputs” for a comparison of generated supply voltage
versus supply current.
+
1µF
LT1080
3
V
+
DRIVER
V
+
EXTERNAL OP AMP
W
U
U
U
+
–
V
–
16
GND
V
–
7
1µF
1080/81 F08
Operating with 5V and 12V
2
4
LT1080
5
6
15
7
1µF
RS232 OUTPUT
–12V OUTPUT
17
3
5V INPUT
8
14
5k
9
5k
16
RS232 OUTPUT
RS232 INPUT
RS232 INPUT
1080/81 • TA03
7
LINER [ LINEAR TECHNOLOGY ]
