LT1080_15 Datasheet, PDF (7/12 Pages) Linear Technology – Advanced Low Power 5V RS232 Dual Driver/Receiver

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.
RS232
INPUT
LT1080
RECEIVER
V_CC
51k* ^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 ^1k*
INPUT
30V
30V
RECEIVER
5k
LOGIC
OUTPUT
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
EXTERNAL OP AMP
V⁺
+
16
GND
V^–
7
1µF
–
V^–
1080/81 F08
* A PTC THERMISTOR WILL ALLOW
CONTINUOUS OVERLOAD OF GREATER THAN ±100V
1080/81 F067
TYPICAL APPLICATIO
12V INPUT*
1µF
LOGIC
INPUTS
LOGIC
OUTPUTS
ON/OFF
Operating with 5V and 12V
2
17
4
3
5V INPUT
LT1080
5
7
–12V OUTPUT
1µF
6
12
15
RS232 OUTPUT
11
8
RS232 OUTPUT
13
14
RS232 INPUT
5k
10
9
RS232 INPUT
18
5k ₁₆
* PIN 1 USED ON LT1081.
1080/81 • TA03
10801fe
7