Datasheet

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LT1780/LT1781

Low Power 5V RS232

Dual Driver/Receiver with

±15kV ESD Protection

TransZorb is a registered trademark of General Instruments, GSI.

Output Waveforms

1780/81 • TA02

DRIVER

OUTPUT

= 3k

= 2500pF

RECEIVER

OUTPUT

= 50pF

INPUT

0.1µF

LOGIC

INPUTS

LOGIC

OUTPUTS

ON/OFF

5V INPUT

OUT

–

OUT

RS232 OUTPUT

RS232 INPUT

1780/81 • TA01

LT1780

ITY

ESCRIPTIO

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.

■

10mA Max Supply Current

■

ESD Protection to IEC 1000-4-2 Level 4

15kV Air Gap,

8kV Contact

■

Uses Small Capacitors: 0.1

■

120kBaud Operation for R

= 3k, C

= 2500pF

■

250kBaud Operation for R

= 3k, C

= 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

■

Portable Computers

■

Battery-Powered Systems

■

Power Supply Generator

■

Terminals

■

Modems

, LTC and LT are registered trademarks of Linear Technology Corporation.

Summary of content (12 pages)

PAGE 1
LT1780/LT1781 Low Power 5V RS232 Dual Driver/Receiver with ±15kV ESD Protection DESCRIPTIO U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 10mA Max Supply Current ESD Protection to IEC 1000-4-2 Level 4 ±15kV Air Gap, ±8kV Contact Uses Small Capacitors: 0.
PAGE 2
LT1780/LT1781 W W W AXI U U ABSOLUTE RATI GS (Note 1) Short-Circuit Duration V + ................................................................... 30 sec V – ................................................................... 30 sec Driver Output .............................................. Indefinite Receiver Output .......................................... Indefinite Operating Temperature Range ..................... 0°C to 70°C Storage Temperature Range ................
PAGE 3
LT1780/LT1781 ELECTRICAL CHARACTERISTICS PARAMETER CONDITIONS Logic Input Current 0.8V ≤ VIN ≤ 2.
PAGE 4
LT1780/LT1781 U W TYPICAL PERFOR A CE CHARACTERISTICS Driver Maximum Output Voltage vs Load Capacitance Driver Minimum Output Voltage vs Load Capacitance 8.0 Driver Output Voltage 10 –4.0 8 7.0 20k BAUD 6.5 60k BAUD 6.0 120k BAUD 5.5 DRIVER OUTPUT VOLTAGE (V) –4.5 PEAK OUTPUT VOLTAGE (V) PEAK OUTPUT VOLTAGE (V) 7.5 120k BAUD –5.0 60k BAUD –5.5 20k BAUD –6.0 –6.5 RL = 3k 6 4 2 0 –2 –4 VCC = 5.5V VCC = 5V VCC = 4.5V OUTPUT HIGH OUTPUT LOW VCC = 4.5V VCC = 5V VCC = 5.5V –6 –8 5.0 –7.
PAGE 5
LT1780/LT1781 U W TYPICAL PERFOR A CE CHARACTERISTICS Driver Leakage in Shutdown Driver Short-Circuit Current 100 ( µA) SHORT-CIRCUIT CURRENT (mA) 30 LEAKAGE CURRENT 10 VOUT = 30V 1 VOUT = –30V 0.
PAGE 6
LT1780/LT1781 U U U 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 Control. 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.
PAGE 7
LT1780/LT1781 U ESD PROTECTIO ESD Test Circuit The RS232 line inputs of the LT1780/LT1781 have on-chip protection from ESD transients up to ±15kV air gap and ±8kV contact tested to IEC-1000-4-2 test methods. The protection structures act to divert the static discharge safely to system ground. In order for the ESD protection to function effectively, the power supply and ground pins of the circuit must be connected to ground through low impedances.
PAGE 8
LT1780/LT1781 U PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. N Package 16-Lead PDIP (Narrow 0.300) (LTC DWG # 05-08-1510) 0.770* (19.558) MAX 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 0.255 ± 0.015* (6.477 ± 0.381) 0.130 ± 0.005 (3.302 ± 0.127) 0.300 – 0.325 (7.620 – 8.255) 0.009 – 0.015 (0.229 – 0.381) ( 0.020 (0.508) MIN +0.035 0.325 –0.015 8.255 +0.889 –0.381 0.045 – 0.065 (1.143 – 1.651) ) 0.065 (1.651) TYP 0.125 (3.175) MIN 0.018 ± 0.003 (0.
PAGE 9
LT1780/LT1781 U PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. SW Package 16-Lead Plastic Small Outline (Wide 0.300) (LTC DWG # 05-08-1620) 0.398 – 0.413* (10.109 – 10.490) 16 15 14 13 12 11 10 9 0.394 – 0.419 (10.007 – 10.643) NOTE 1 0.291 – 0.299** (7.391 – 7.595) 1 2 3 4 5 6 7 8 0.093 – 0.104 (2.362 – 2.642) 0.010 – 0.029 × 45° (0.254 – 0.737) 0.037 – 0.045 (0.940 – 1.143) 0° – 8° TYP 0.009 – 0.013 (0.229 – 0.330) NOTE 1 0.016 – 0.050 (0.406 – 1.
PAGE 10
LT1780/LT1781 U PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. SW Package 18-Lead Plastic Small Outline (Wide 0.300) (LTC DWG # 05-08-1620) 0.447 – 0.463* (11.354 – 11.760) 18 17 16 15 14 13 12 11 10 0.394 – 0.419 (10.007 – 10.643) SEE NOTE 0.291 – 0.299** (7.391 – 7.595) 1 2 3 4 5 6 7 8 9 0.093 – 0.104 (2.362 – 2.642) 0.010 – 0.029 × 45° (0.254 – 0.737) 0.037 – 0.045 (0.940 – 1.143) 0° – 8° TYP 0.009 – 0.013 (0.229 – 0.330) NOTE 1 0.016 – 0.050 (0.
PAGE 11
LT1780/LT1781 U PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. S Package 16-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.386 – 0.394* (9.804 – 10.008) 16 15 14 13 12 11 10 9 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 1 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 2 3 4 5 6 0.053 – 0.069 (1.346 – 1.752) 0.014 – 0.019 (0.355 – 0.483) 8 0.004 – 0.010 (0.101 – 0.254) 0° – 8° TYP 0.016 – 0.050 0.
PAGE 12
LT1780/LT1781 U TYPICAL APPLICATIO Supporting an LT1039 (Triple Driver/Receiver) SHUTDOWN 5V 18 TTL INPUT TTL INPUT VCC ON/OFF LT1780 17 11 8 12 15 18 RS232 OUTPUT TTL INPUT RS232 OUTPUT TTL INPUT TTL INPUT TTL OUTPUT 14 13 RS232 INPUT TTL OUTPUT VCC ON/OFF LT1039 15 4 13 6 11 8 16 3 5k TTL OUTPUT RS232 INPUT TTL OUTPUT 14 5 5k 2 1µF 4 5 1µF 6 RS232 OUTPUT RS232 OUTPUT RS232 OUTPUT RS232 INPUT 30k 9 10 17 RS232 INPUT 30k C1+ TTL OUTPUT 7 12 RS232 INPUT 30