LT1080/LT1081
U
W U U
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 VCC to force a definite logic level when the
receiver output is in a high impedance state.
The generated driver supplies (V+ and V–) may be used to
powerexternalcircuitrysuchasotherRS232driversorop
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.
V
CC
LT1080
RECEIVER
CMOS
51k*
LOGIC
RS232
INPUT
LOGIC
OUTPUT
EXTERNAL OP AMP
+
3
1µF
+
LT1080
V
ON/OFF
INPUT
+
–
V
V
DRIVER
+
–
* FORCES LOGIC INPUT STATE WHEN V
IS LOW
ON/OFF
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.
16
–
GND
V
7
1µF
RECEIVER
5k
1k*
RS232
INPUT
1080/81 F08
LOGIC
OUTPUT
30V
30V
* A PTC THERMISTOR WILL ALLOW
CONTINUOUS OVERLOAD OF GREATER THAN ±100V
1080/81 F067
U
TYPICAL APPLICATIO
Operating with 5V and 12V
2
17
12V INPUT*
5V INPUT
4
3
LT1080
5
7
–12V OUTPUT
1µF
1µF
6
12
15
RS232 OUTPUT
LOGIC
INPUTS
11
13
8
RS232 OUTPUT
RS232 INPUT
14
5k
5k
LOGIC
OUTPUTS
10
18
9
RS232 INPUT
16
ON/OFF
1080/81 • TA03
* PIN 1 USED ON LT1081.
7
Linear [ Linear ]
