ANALOG DEVICES LT 1785 CS8 Datasheet

LT1785/LT1785A/

LT1791/LT1791A

60V Fault Protected

RS485/RS422 Transceivers

FEATURES

n

Protected from Overvoltage Line Faults to ±60V

n

Pin Compatible with LTC485 and LTC491

n

High Input Impedance Supports Up to 128 Nodes

n

No Damage or Latchup to ESD

IEC-1000-4-2 Level 4: ±15kV Air Discharge
IEC-1000-4-2 Level 2: ±4kV Contact Discharge

n

Controlled Slew Rates for EMI Emissions Control

n

Guaranteed High Receiver Output State for Floating,

Shorted or Inactive Inputs

n

Outputs Assume a High Impedance When Off or

Powered Down

n

Drives Low Cost, Low Impedance Cables

n

Short-Circuit Protection on All Outputs

n

Thermal Shutdown Protection

n

Guaranteed Operation to 125°C

APPLICATIONS

n

Industrial Control Data Networks

n

CAN Bus Applications

n

HVAC Controls

L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.

DESCRIPTION

The LT®1785/LT1791 are half-duplex and full-duplex differ­ential bus transceivers for RS485 and RS422 applications
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 out­putscontrol EMI emissions and improve data transmis­sion integrity on improperly terminated lines. Drivers are
specifi ed to operate with inexpensive cables as low as
72Ω 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 eliminates
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.

TYPICAL APPLICATION

V

RO1

RE1

DE1

DI1

RO2

RE2

DE2

DI2

RX

LT1785

TX

RX

LT1785

TX

CC1

GND1

V

CC2

GND2

R

R

TERM

TERM

Normal Operation Waveforms at 250kBaud

RO

Y-Z

DI

178591 TA02

178591 TA01

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1

LT1785/LT1785A/
LT1791/LT1791A

ABSOLUTE MAXIMUM RATINGS

(Note 1)

Supply Voltage (VCC) ................................................18V

Receiver Enable Input Voltage ...................... –0.3V to 6V

Driver Enable Input Voltage .......................... –0.3V to 6V

Driver Input Voltage ................................... –0.3V to 18V

Receiver Input Voltage ................................ –60V to 60V

Driver Output Voltage .................................. –60V to 60V

Receiver Output Voltage ...................–0.3V to (V

+ 6V)

CC

PIN CONFIGURATION

TOP VIEW

RO

1

2

3

4

R

D

8-LEAD PLASTIC SO

RE

DE

DI

N8 PACKAGE
8-LEAD PDIP

T

= 150°C, θJA = 130°C/W (N8)

JMAX

= 150°C, θJA = 150°C/W (S8)

T

JMAX

V

8

B

7

A

6

GND

5

S8 PACKAGE

CC

Operating Temperature Range
LT1785C/LT1791C/

LT1785AC/LT1791AC .................................... 0°C to 70°C

LT1785I/LT1791I/

LT1785AI/LT1791AI .................................. –40°C to 85°C

LT1785H/LT1791H/

LT1785AH/LT1791AH ............................. –40°C to 125°C

Storage Temperature Range ................... –65°C to 150°C

Lead Temperature (Soldering, 10 sec) ..................300°C

TOP VIEW

1

NC

2

RO

3

RE

4

DE

5

DI

6

GND

7

GND

N PACKAGE

14-LEAD PDIP

T

= 150°C, θJA = 130°C/W (N)

JMAX

= 150°C, θJA = 150°C/W (S)

T

JMAX

14

V

CC

R

13

NC

12

A

11

B

10

9

8

S PACKAGE

Z

Y

NC

D

14-LEAD PLASTIC SO

ORDER INFORMATION

LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LT1785CN8#PBF LT1785CN8#TRPBF 1785 8-Lead PDIP 0°C to 70°C

LT1785CS8#PBF LT1785CS8#TRPBF 1785 8-Lead Plastic SO 0°C to 70°C

LT1785IN8#PBF LT1785IN8#TRPBF 1785I 8-Lead PDIP –40°C to 85°C

LT1785IS8#PBF LT1785IS8#TRPBF 1785I 8-Lead Plastic SO –40°C to 85°C

LT1785ACN8#PBF LT1785ACN8#TRPBF 1785A 8-Lead PDIP 0°C to 70°C

LT1785ACS8#PBF LT1785ACS8#TRPBF 1785A 8-Lead Plastic SO 0°C to 70°C

LT1785AIN8#PBF LT1785AIN8#TRPBF 1785AI 8-Lead PDIP –40°C to 85°C

LT1785AIS8#PBF LT1785AIS8#TRPBF 1785AI 8-Lead Plastic SO –40°C to 85°C

LT1785HN8#PBF LT1785HN8#TRPBF 1785H 8-Lead PDIP –40°C to 125°C

LT1785HS8#PBF LT1785HS8#TRPBF 1785H 8-Lead Plastic SO –40°C to 125°C

LT1785AHN8#PBF LT1785AHN8#TRPBF 1785AH 8-Lead PDIP –40°C to 125°C

LT1785AHS8#PBF LT1785AHS8#TRPBF 1785AH 8-Lead Plastic SO –40°C to 125°C

LT1791CN#PBF LT1791CN#TRPBF 1791 14-Lead PDIP 0°C to 70°C

LT1791CS#PBF LT1791CS#TRPBF 1791 14-Lead Plastic SO 0°C to 70°C

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LT1785/LT1785A/

LT1791/LT1791A

ORDER INFORMATION

LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LT1791IN#PBF LT1791IN#TRPBF 1791I 14-Lead PDIP –40°C to 85°C

LT1791IS#PBF LT1791IS#TRPBF 1791I 14-Lead Plastic SO –40°C to 85°C

LT1791ACN#PBF LT1791ACN#TRPBF 1791A 14-Lead PDIP 0°C to 70°C

LT1791ACS#PBF LT1791ACS#TRPBF 1791A 14-Lead Plastic SO 0°C to 70°C

LT1791AIN#PBF LT1791AIN#TRPBF 1791AI 14-Lead PDIP –40°C to 85°C

LT1791AIS#PBF LT1791AIS#TRPBF 1791AI 14-Lead Plastic SO –40°C to 85°C

LT1791HN#PBF LT1791HN#TRPBF 1791H 14-Lead PDIP –40°C to 125°C

LT1791HS#PBF LT1791HS#TRPBF 1791H 14-Lead Plastic SO –40°C to 125°C

LT1791AHN#PBF LT1791AHN#TRPBF 1791AH 14-Lead PDIP –40°C to 125°C

LT1791AHS#PBF LT1791AHS#TRPBF 1791AH 14-Lead Plastic SO –40°C to 125°C

LEAD BASED FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LT1785CN8 LT1785CN8#TR 1785 8-Lead PDIP 0°C to 70°C

LT1785CS8 LT1785CS8#TR 1785 8-Lead Plastic SO 0°C to 70°C

LT1785IN8 LT1785IN8#TR 1785I 8-Lead PDIP –40°C to 85°C

LT1785IS8 LT1785IS8#TR 1785I 8-Lead Plastic SO –40°C to 85°C

LT1785ACN8 LT1785ACN8#TR 1785A 8-Lead PDIP 0°C to 70°C

LT1785ACS8 LT1785ACS8#TR 1785A 8-Lead Plastic SO 0°C to 70°C

LT1785AIN8 LT1785AIN8#TR 1785AI 8-Lead PDIP –40°C to 85°C

LT1785AIS8 LT1785AIS8#TR 1785AI 8-Lead Plastic SO –40°C to 85°C

LT1785HN8 LT1785HN8#TR 1785H 8-Lead PDIP –40°C to 125°C

LT1785HS8 LT1785HS8#TR 1785H 8-Lead Plastic SO –40°C to 125°C

LT1785AHN8 LT1785AHN8#TR 1785AH 8-Lead PDIP –40°C to 125°C

LT1785AHS8 LT1785AHS8#TR 1785AH 8-Lead Plastic SO –40°C to 125°C

LT1791CN LT1791CN#TR 1791 14-Lead PDIP 0°C to 70°C

LT1791CS LT1791CS#TR 1791 14-Lead Plastic SO 0°C to 70°C

LT1791IN LT1791IN#TR 1791I 14-Lead PDIP –40°C to 85°C

LT1791IS LT1791IS#TR 1791I 14-Lead Plastic SO –40°C to 85°C

LT1791ACN LT1791ACN#TR 1791A 14-Lead PDIP 0°C to 70°C

LT1791ACS LT1791ACS#TR 1791A 14-Lead Plastic SO 0°C to 70°C

LT1791AIN LT1791AIN#TR 1791AI 14-Lead PDIP –40°C to 85°C

LT1791AIS LT1791AIS#TR 1791AI 14-Lead Plastic SO –40°C to 85°C

LT1791HN LT1791HN#TR 1791H 14-Lead PDIP –40°C to 125°C

LT1791HS LT1791HS#TR 1791H 14-Lead Plastic SO –40°C to 125°C

LT1791AHN LT1791AHN#TR 1791AH 14-Lead PDIP –40°C to 125°C

LT1791AHS LT1791AHS#TR 1791AH 14-Lead Plastic SO –40°C to 125°C

Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. *The temperature grade is identifi ed by a label on the shipping container.
For more information on lead free part marking, go to:

This product is only offered in trays. For more information go to:

http://www.linear.com/leadfree/

http://www.linear.com/packaging/

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LT1785/LT1785A/
LT1791/LT1791A

DC ELECTRICAL CHARACTERISTICS

The l denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at T

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

V

V

V

∆|V

V

V

I

IN1

I

IN2

V

∆V

V

V

R

I

SC

I

CC

OD1

OD2

OD

OC

IH

IL

TH

TH

OH

OL

IN

Differential Driver Output Voltage (Unloaded) IO = 0

Differential Driver Output Voltage (With Load) R = 50 (RS422), Figure 1

Change in Magnitude of Driver Differential Output
Voltage for Complementary Output States

Driver Common Mode Output Voltage R = 27 or R = 50, Figure 1

| Change in Magnitude of Driver Common Mode Output

OC

Voltage for Complementary Output States
Input High Voltage DI, DE, RE
Input Low Voltage DI, DE, RE
Input Current DI, DE, RE

Input Current (A, B); (LT1791 or LT1785 with DE = 0V) VIN = 12V

Differential Input Threshold Voltage for Receiver LT1785/LT1791: –7V ≤ VCM ≤ 12V

Receiver Input Hysteresis –7V < VCM < 12V 20 mV

Receiver Output High Voltage IO = –400µA, VID = 200mV

Receiver Output Low Voltage IO = 1.6mA, VID = –200mV

Three-State (High Impedance) Output Current at
Receiver 0V < V

OUT

< 6V

Receiver Input Resistance (LT1791) –7V ≤ VCM ≤ 12V

LT1785 –7V ≤ VCM ≤ 12V

RS485 Unit Load 0.25

Driver Short-Circuit Current V

Driver Output Fault Current VO = 60V

Receiver Short-Circuit Current 0V ≤ V

Driver Three-State Output Current –7V ≤ V

Supply Current No Load, RE = 0V, DE = 5V

= 25°C, VCC = 5V.

A

R = 27 (RS485), Figure 1
R = 18

R = 27 or R = 50, Figure 1

R = 27 or R = 50, Figure 1

V

= –7V

IN

–60V ≤ V

LT1785A/LT1791A: –7V ≤ V

RE > 2V or Power Off

– 60V ≤ V

= HIGH, Force VO = –7V

OUT

V

= LOW, Force VO = 12V

OUT

V

= –60V

O

O

–60V ≤ V

No Load, RE = 5V, DE = 5V
No Load, RE = 0V, DE = 0V
No Load, RE = 5V, DE = 0V

≤ 60V

IN

CM

≤ V

≤ 12V

O

≤ 60V

O

≤ 60V

CC

CM

≤ 12V

l

l

2.0

l

1.5

l

1.2

l

l

2 2.5 3 V

l

l

2V

l

l

l
l

–0.15

l

–6

l

–0.2

l

–0.2

l

3.5 4 V

l

l

–1 1 µA

l

85 125

l

50 90 kΩ

l

35

l

35

l
l

–6

l

l

–0.2

l

–6

l
l
l
l

4.1 5 V

2.70

2.45

2.2

0.2 V

0.2 V

0.8 V

5µA

0.15

0.3

–0.08

6

0.2
0

0.3 0.5 V

125

250
250

6mA

±35 mA

0.3
6

5.5

5.5

4.5

0.2

9
9
8

0.3

mA
mA
mA

kΩ
kΩ

mA
mA

mA

mA
mA

mA
mA
mA
mA

V
V
V

V
V

4

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LT1785/LT1785A/

LT1791/LT1791A

SWITCHING CHARACTERISTICS

The l denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at T

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

t

PLH

t

PHL

t

SKEW

, t

t

r

f

t

ZH

t

ZL

t

LZ

t

HZ

t

PLH

t

PHL

t

SKD

t

ZL

t

ZH

t

LZ

t

HZ

f

MAX

t

SHDN

t

ZH(SHDN)

t

ZL(SHDN)

t

ZH(SHDN)

t

ZL(SHDN)

Driver Input to Output Figures 3, 5

Driver Input to Output Figures 3, 5

Driver Output to Output Figures 3, 5 100 ns

Driver Rise or Fall Time Figures 3, 5

Driver Enable to Output High Figures 4, 6

Driver Enable to Output Low Figures 4, 6

Driver Disable Time from Low Figures 4, 6

Driver Disable Time from High Figures 4, 6

Receiver Input to Output Figures 3, 7

Receiver Input to Output Figures 3, 7

Differential Receiver Skew 200 ns

Receiver Enable to Output Low Figures 2, 8

Receiver Enable to Output High Figures 2, 8

Receiver Disable from Low Figures 2, 8

Receiver Disable from High Figures 2, 8

Maximum Data Rate

Time to Shut Down Figures 2, 6, 8 3 µs
Driver Enable from Shutdown to Output High Figures 2, 6; RE = 5V 12 µs
Driver Enable from Shutdown to Output Low Figures 2, 6; RE = 5V 12 µs

Receiver Enable from Shutdown to Output High Figures 2, 8; DE = 0V 4 µs

Receiver Enable from Shutdown to Output Low Figures 2, 8; DE = 0V 4 µs

= 25°C, VCC = 5V.

A

l

l

l

200 800 2000 ns

l

l

l

l

l

l

l

l

l

l

l

250 kbps

700 2000 ns

700 2000 ns

500 3000 ns

800 3000 ns

200 5000 ns

800 5000 ns

400 900 ns

400 900 ns

300 1000 ns

300 1000 ns

400 1000 ns

400 1000 ns

Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.

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