LT1780/LT1781
Low Power 5V RS232
Dual Driver/Receiver with
±15kV ESD Protection
DESCRIPTIO
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FEATURES
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10mA Max Supply Current
ESD Protection to IEC 1000-4-2 Level 4
±15kV Air Gap, ±8kV Contact
Uses Small Capacitors: 0.1µF
120kBaud Operation for RL = 3k, CL = 2500pF
250kBaud Operation for RL = 3k, CL = 1000pF
Outputs Withstand ±30V Without Damage
CMOS Comparable Low Power: 40mW
Operates from a Single 5V Supply
Rugged Bipolar Design
Outputs Assume a High Impedance State When Off
or Powered Down
Meets All RS232 Specifications
Available With or Without Shutdown
Absolutely No Latch-up
The LT1780/LT1781 are direct upgrades to the LT1180A/
LT1181A, LT1280A/LT1281A and LT1381 for applications
which require the utmost ESD protection.
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APPLICATI
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The LT®1780/LT1781 are dual RS232 driver/receiver pairs
with integral charge pump to generate RS232 voltage
levels from a single 5V supply. Using only 0.1µF external
capacitors, these circuits consume only 40mW of power,
and can operate to 120kbaud even while driving heavy
capacitive loads. New ESD structures on the chip allow the
LT1780/LT1781 to survive ±15kV air gap and ±8kV contact ESD tests per IEC 1000-4-2, eliminating the need for
costly TransZorbs® on the RS232 line pins. The LT1780/
LT1781 are fully compliant with EIA RS232 standards.
Driver outputs are protected from overload, and can be
shorted to ground or up to ±30V without damage. During
SHUTDOWN or power-off conditions, driver and receiver
outputs are in a high impedance state, allowing line
sharing.
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Portable Computers
Battery-Powered Systems
Power Supply Generator
Terminals
Modems
The LT1781 is available in 16-pin DIP,SO and SW packages. The LT1780 is supplied in 18-pin DIP and SW
packages for applications which require SHUTDOWN.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TransZorb is a registered trademark of General Instruments, GSI.
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TYPICAL APPLICATI
2
0.1µF
17
4
3
5
0.1µF
7
15
11
8
13
14
RS232 OUTPUT
RECEIVER
OUTPUT
R
CL = 50pF
RS232 OUTPUT
RS232 INPUT
INPUT
5k
LOGIC
OUTPUTS
10
ON/OFF
V – OUT
DRIVER
OUTPUT
RL = 3k
CL = 2500pF
0.1µF
6
12
LOGIC
INPUTS
V + OUT
0.1µF
LT1780
Output Waveforms
5V INPUT
18
9
5k
RS232 INPUT
1780/81 • TA02
16
1780/81 • TA01
1
