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LT1781 Schematic ( PDF Datasheet ) - Linear Technology

Teilenummer LT1781
Beschreibung Low Power 5V RS232 Dual Driver/Receiver with 15kV ESD Protection
Hersteller Linear Technology
Logo Linear Technology Logo 




Gesamt 12 Seiten
LT1781 Datasheet, Funktion
FEATURES
s 10mA Max Supply Current
s ESD Protection to IEC 1000-4-2 Level 4
±15kV Air Gap, ±8kV Contact
s Uses Small Capacitors: 0.1µF
s 120kBaud Operation for RL = 3k, CL = 2500pF
s 250kBaud Operation for RL = 3k, CL = 1000pF
s Outputs Withstand ±30V Without Damage
s CMOS Comparable Low Power: 40mW
s Operates from a Single 5V Supply
s Rugged Bipolar Design
s Outputs Assume a High Impedance State When Off
or Powered Down
s Meets All RS232 Specifications
s Available With or Without Shutdown
s Absolutely No Latch-up
APPLICATI S
s Portable Computers
s Battery-Powered Systems
s Power Supply Generator
s Terminals
s Modems
TYPICAL APPLICATI
0.1µF
2
4
17
3
0.1µF
LOGIC
INPUTS
LOGIC
OUTPUTS
ON/OFF
5
6
12
11
13
10
18
LT1780
7
15
8
14
5k
9
5k 16
5V INPUT
0.1µF
V+ OUT
0.1µF
V OUT
RS232 OUTPUT
RS232 OUTPUT
RS232 INPUT
RS232 INPUT
1780/81 • TA01
LT1780/LT1781
Low Power 5V RS232
Dual Driver/Receiver with
±15kV ESD Protection
DESCRIPTIO
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 con-
tact 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.
The LT1780/LT1781 are direct upgrades to the LT1180A/
LT1181A, LT1280A/LT1281A and LT1381 for applications
which require the utmost ESD protection.
The LT1781 is available in 16-pin DIP,SO and SW pack-
ages. 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.
DRIVER
OUTPUT
RL = 3k
CL = 2500pF
RECEIVER
RCOL U=T5P0UpTF
INPUT
Output Waveforms
1780/81 • TA02
1






LT1781 Datasheet, Funktion
LT1780/LT1781
PI FU CTIO S
VCC: 5V Input Supply Pin. This pin should be decoupled
with a 0.1µF ceramic capacitor close to the package pin.
Insufficient supply bypassing can result in low output
drive levels and erratic charge pump operation.
GND: Ground Pin.
ON/OFF: A TTL/CMOS Compatible Operating Mode Con-
trol. A logic low puts the LT1780 in SHUTDOWN mode.
Supply current drops to zero and both driver and receiver
outputs assume a high impedance state. A logic high fully
enables the device.
V+: Positive Supply Output (RS232 Drivers).
V+ 2VCC – 1.5V. This pin requires an external charge
storage capacitor C 0.1µF, tied to ground or VCC. Larger
value capacitors may be used to reduce supply ripple. With
multiple transceivers, the V+ and V pins may be paralleled
into common capacitors.
V: Negative Supply Output (RS232 Drivers).
V –(2VCC – 2.5V). This pin requires an external charge
storage capacitor C 0.1µF. Larger value capacitors may
be used to reduce supply ripple. With multiple transceiv-
ers, the V+ and V pins may be paralleled into common
capacitors.
TR1 IN, TR2 IN: RS232 Driver Input Pins. These inputs are
TTL/CMOS compatible. Inputs should not be allowed to
float. Tie unused inputs to VCC.
TR1 OUT, TR2 OUT: Driver Outputs at RS232 Voltage
Levels. Driver output swing meets RS232 levels for loads
up to 3k. Slew rates are controlled for lightly loaded lines.
Output current capability is sufficient for load conditions
up to 2500pF. Outputs are in a high impedance state when
in SHUTDOWN mode or VCC = 0V. Outputs are fully short-
circuit protected from V + 30V to V + – 30V. Applying
higher voltages will not damage the device if the overdrive
is moderately current limited. Short circuits on one
output can load the power supply generator and may
disrupt the signal levels of the other outputs. The driver
outputs are protected against ESD to IEC-1000-4-2
Level 4 discharges.
REC1 IN, REC2 IN: Receiver Inputs. These pins accept
RS232 level signals (±30V) into a protected 5k terminat-
ing resistor. The receiver inputs are protected against ESD
to IEC-1000-4-2 Level 4 discharges. Each receiver pro-
vides 0.4V of hysteresis for noise immunity. Open receiver
inputs result in a logic high receiver output state.
REC1 OUT, REC2 OUT: Receiver outputs with TTL/CMOS
Voltage Levels. Outputs are in a high impedance state
when in SHUTDOWN mode to allow data line sharing.
Outputs are fully short-circuit protected to ground or VCC
with the power ON, OFF or in the SHUTDOWN mode.
C1+, C1, C2 +, C2 : Commutating Capacitor Inputs.
These pins require two external capacitors C 0.1µF: one
from C1+ to C1and another from C2+ to C2 . C1 should
be deleted if a separate 12V supply is available and
connected to pin C1+. Similarly, C2 should be deleted if a
separate – 12V supply is connected to pin V .
6

6 Page









LT1781 pdf, datenblatt
LT1780/LT1781
TYPICAL APPLICATIO
Supporting an LT1039 (Triple Driver/Receiver)
SHUTDOWN
18 ON/OFF
VCC
LT1780
11
TTL INPUT
17
8
RS232 OUTPUT
5V
18
VCC
ON/OFF 17
LT1039
15
TTL INPUT
4
RS232 OUTPUT
12
TTL INPUT
15 RS232 OUTPUT
13
TTL INPUT
6
RS232 OUTPUT
13
TTL OUTPUT
10
TTL OUTPUT
14
RS232 INPUT
5k
9
RS232 INPUT
5k
2 C1+
1µF 4 C1
5 C2+
V+ 3
1µF 6 C2
V7
GND
16
1µF
11
TTL INPUT
16
TTL OUTPUT
14
TTL OUTPUT
12
TTL OUTPUT
1 V+
9 V
1µF
8
RS232 OUTPUT
3
RS232 INPUT
30k
5
RS232 INPUT
30k
7
RS232 INPUT
30k
GND
10
1780/81 • TA04
RELATED PARTS
PART NUMBER
LT1137A
LTC1383
LTC1387
DESCRIPTION
3Driver/5Receiver RS232 Transceiver
5V Low Power RS232 2Driver/2Receiver Transceiver
Single 5V RS232/RS485 Multiprotocol Transceiver
COMMENTS
IEC-1000-4-2 Level 4 ESD Compliance
Low Supply Current ICC = 220µA
Configurable as Dual RS232 or Single RS485 Transceiver
12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX:(408)434-0507 q www.linear-tech.com
17801f LT/TP 0498 4K • PRINTED IN USA
© LINEAR TECHNOLOGY CORPORATION 1998

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