LT1080, LT1081
ADVANCED LOW-POWER
5-V DUAL EIA-232 DRIVER/RECEIVERS
SLLS050A – D3121, SEPTEMBER 1989 – REVISED FEBRUARY 1991
APPLICATION INFORMATION
LT1080
Driver 1
Logic
Transmit/Receive
Line
LT1080
Receiver 2
EIA-232
Transmit/Receive
Line
Logic
Inverter
ON/OFF
(transmit/receive)
Figure 17. Transceiver
To protect against receiver input overloads in excess of
±
30 V, a voltage clamp can be placed on the data line and
still maintain EIA-232 compatibility (see Figure 18).
When driving CMOS logic from a receiver that will be used in the shutdown mode and when there is no other active
receiver on the line, a 51-kΩ 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 (see Figure 19).
The generated driver supplies (V
S +
and V
S –
) may be used to power external circuitry such as other EIA-232 drivers
or operational amplifiers (see Figure 20). They should be loaded with care, since excessive loading can cause the
generated supply voltages to drop, causing the EIA-232 driver output voltages to fall below EIA-232 requirements.
See Figure 5 for a comparison of generated supply voltage versus supply current.
VCC
1 kΩ
(see Note A)
Logic
Output
5 kΩ
EIA-232
Input
ON/OFF
LT1080
Receiver
EIA-232
Input
51 kΩ
(see Note A)
CMOS
Logic
30 V
30 V
Logic
Output
NOTE A: A PTC thermistor will allow continuous overload of
greater than
±
100 V.
NOTE A: Forces logic input state when VI is low.
Figure 18. Input Overload Protection
Figure 19. Forcing a Definite Logic Level
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