LT1785 Linear Technology, LT1785 Datasheet

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LT1785

Manufacturer Part Number
LT1785
Description
60V Fault Protected RS485/RS422 Transceivers
Manufacturer
Linear Technology
Datasheet

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0
APPLICATIO S
FEATURES
TYPICAL APPLICATIO
Protected from Overvoltage Line Faults to 60V
Pin Compatible with LTC485 and LTC491
High Input Impedance Supports Up to 128 Nodes
No Damage or Latchup to ESD
Controlled Slew Rates for EMI Emissions Control
Guaranteed High Receiver Output State for Floating,
Shorted or Inactive Inputs
Outputs Assume a High Impedance When Off or
Powered Down
Drives Low Cost, Low Impedance Cables
Short-Circuit Protection on All Outputs
Thermal Shutdown Protection
Industrial Control Data Networks
CAN Bus Applications
HVAC Controls
IEC-1000-4-2 Level 4: 15kV Air Discharge
IEC-1000-4-2 Level 2: 4kV Contact Discharge
RO1
RO2
RE1
DE1
RE2
DE2
DI1
DI2
U
TX
TX
LT1785
LT1785
RX
RX
U
V
V
GND1
GND2
CC2
CC1
R
R
TERM
TERM
1785/91 TA01
The LT
ferential bus transceivers for RS485 and RS422 applica-
tions which feature on-chip protection from overvoltage
faults on the data transmission lines. Receiver input and
driver output pins can withstand voltage faults up to 60V
with respect to ground with no damage to the device.
Faults may occur while the transceiver is active, shut down
or powered off.
Data rates to 250kbaud on networks of up to 128 nodes are
supported. Controlled slew rates on the driver outputs
control EMI emissions and improve data transmission
integrity on improperly terminated lines. Drivers are speci-
fied to operate with inexpensive cables as low as 72
characteristic impedance.
The LT1785A/LT1791A devices have “fail-safe” receiver
inputs to guarantee a receiver output high for shorted,
open or inactive data lines. On-chip ESD protection elimi-
nates need for external protection devices.
The LT1785/LT1785A are available in 8-lead DIP and SO
packages and the LT1791/LT1791A in 14-lead DIP and SO
packages.
DESCRIPTIO
, LTC and LT are registered trademarks of Linear Technology Corporation.
®
Y-Z
1785/LT1791 are half-duplex and full-duplex dif-
RO
RS485/RS422 Transceivers
DI
Normal Operation Waveforms at 250kBaud
60V Fault Protected
U
LT1785/LT1785A
LT1791/LT1791A
1785/91 TA02
1

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LT1785 Summary of contents

Page 1

... On-chip ESD protection elimi- nates need for external protection devices. The LT1785/LT1785A are available in 8-lead DIP and SO packages and the LT1791/LT1791A in 14-lead DIP and SO packages. , LTC and LT are registered trademarks of Linear Technology Corporation. ...

Page 2

... JMAX JA Consult factory for Military grade parts (Note 1) Operating Temperature Range LT1785C/LT1791C/ LT1785AC/LT1791AC ............................. LT1785I/LT1791I ............................... – Storage Temperature Range ................ – 150 C Lead Temperature (Soldering, 10 sec)................. 300 ORDER PART NUMBER LT1785CN8 NC 1 LT1785CS8 RO ...

Page 3

... Change in Magnitude of Driver Common Mode OC Output Voltage for Complementary Output States V Input High Voltage IH V Input Low Voltage IL I Input Current IN1 I Input Current (A, B); (LT1791 or LT1785 with IN2 DE = 0V) V Differential Input Threshold Voltage for Receiver TH V Receiver Input Hysteresis TH V Receiver Output High Voltage OH V ...

Page 4

... LT1785/LT1785A LT1791/LT1791A U SWITCHI G CHARACTERISTICS The denotes specifications which apply over the full operating temperature range, otherwise specifications are SYMBOL PARAMETER t Driver Input to Output PLH t Driver Input to Output PHL t Driver Output to Output SKEW Driver Rise or Fall Time Driver Enable to Output High ...

Page 5

... DE: Driver Output Enable. TTL level logic input. A logic high on DE enables normal operation of the driver outputs (Y and Z on LT1791, A and B on LT1785). A logic low level at DE places the driver output pins into a high impedance LT1785/LT1785A ...

Page 6

... For CAN applications, output Y is the CANL output node. Z: Driver Output. The Z driver output is opposite in phase to the driver input DI. In the LT1785 driver output Z is internally connected to receiver input B. The driver output assumes a high impedance state when DE is low, power is off or thermal shutdown is activated ...

Page 7

... LT1785 Receiving INPUTS A – 200mV 200mV Open 0mV for LT1785A U W SWITCHI WAVEFOR 1 – OUTPUT B UNDER TEST RE 15pF 1785/91 F03 LT1791 OUTPUTS ...

Page 8

... Figure 8. Receiver Enable and Disable Times W U cally – 12.5V. Replacement of standard RS485 transceiver components with the LT1785 or LT1791 devices eliminates field failures due to overvoltage faults or the use of costly external protection devices. The limited overvoltage tolerance of CMOS RS485 transceivers makes implementation of effective external protection networks difficult without interfering with proper data network performance within the – ...

Page 9

... The LT1785/LT1791 I/O pins have on-chip ESD protection circuitry to eliminate field failures caused by discharges to exposed ports and cables in application environments. The LT1785 pins A and B and the LT1791 driver output pins Y and Z are protected to IEC-1000-4-2 level 2. These pins will survive multiple ESD strikes of 15kV air dis- charge or 4kV contact discharge ...

Page 10

... LT1785/LT1785A LT1791/LT1791A U U APPLICATIO S I FOR ATIO PACKAGE DESCRIPTION 0.300 – 0.325 (7.620 – 8.255) 0.065 (1.651) 0.009 – 0.015 TYP (0.229 – 0.381) +0.035 0.325 –0.015 0.100 0.010 +0.889 8.255 (2.540 0.254) –0.381 *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS ...

Page 11

... DWG # 05-08-1610) (8.560 – 8.738 0.228 – 0.244 (5.791 – 6.197 0.053 – 0.069 (1.346 – 1.752) 0 – 8 TYP 0.014 – 0.019 (0.355 – 0.483) LT1785/LT1785A LT1791/LT1791A 0.770* (19.558) MAX 0.045 – 0.065 (1.143 – 1.651) ...

Page 12

... LTC1685 52Mbps RS485 Half-Duplex Transceiver LTC1687 52Mbps RS485 Full-Duplex Transceiver Linear Technology Corporation 12 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear-tech.com LT1785 LT1785 Figure 10. Half-Duplex RS485 Network Operation ...

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