LT1080, LT1081
ADVANCED LOW-POWER
5-V DUAL EIA-232 DRIVER/RECEIVERS
SLLS050A – D3121, SEPTEMBER 1989 – REVISED FEBRUARY 1991
APPLICATION INFORMATION
The driver output stage of the LT1080 offers significantly improved protection over older bipolar and CMOS designs
(see Figures 13 and 14). In addition to limiting current, the driver output can be externally forced to
±
30 V without
damage, excessive current flow, or supply disruption. Some drivers have diodes connected between the outputs and
the supplies, allowing externally applied voltages to cause excessive supply voltage to develop.
V+
30 V
– 30 V
Output Can Be
Externally Forced
V–
With Some Drivers,
Externally Applied
Voltage Can Force
the Supplies
Figure 13. LT1080/LT1081 Driver
Figure 14. Older EIA-232 Drivers
and CMOS Drivers
Placing the LT1080 in the shutdown mode (pin 18 low) puts both the driver and receiver outputs in a high-impedance
state. This allows for bus operation and transceiver applications (see Figures 15 –17). The shutdown mode also drops
input supply current (V
CC
) to near zero for power-conscious systems.
LT1080
Receiver 1
EIA-232
Input A
LT1080
Receiver 2
EIA-232
Input B
Logic
Inverter
ON/OFF
(channel select)
Input
Logic
Output
Logic
Input B
Logic
Inverter
ON/OFF
(channel select)
Input
Logic
Input A
LT1080
Driver 2
LT1080
Driver 1
EIA-232
Transmission
Line
Figure 15. Sharing a Receiver Line
Figure 16. Sharing a Transmitter Line
2–8
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