ANALOG DEVICES LT 1785 IS8 Datasheet

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Page 1

LT1785/LT1785A/

LT1791/LT1791A

60V Fault Protected

RS485/RS422 Transceivers

FeaTures

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

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

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

Controlled Slew Rates for EMI Emissions Control

Guaranteed High Receiver Output State for Floating,

Shorted or Inactive Inputs (LT1785A/LT1791A)

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

Guaranteed Operation to 125°C

applicaTions

Industrial Control Data Networks

CAN Bus Applications

HVAC Controls

L, LT, LTC, LTM, µModule, Linear Technology and the Linear logo 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 differ- ential 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.

rates to 250kbaud on networks of up to 128 nodes

Data are supported. Controlled slew rates on the driver out putscontrol EMI emissions and improve data transmission integrity on improperly terminated lines. Drivers are speciﬁed 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

RO1

RE1

DE1

DI1

RO2

RE2

DE2

DI2

LT1785

CC1

GND1

CC2

GND2

TERM

Normal Operation Waveforms at 250kBaud

Y-Z

178591 TA01

For more information www.linear.com/LT1785

178591 TA02

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Page 2

LT1785/LT1785A/

TOP VIEW

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)

pin conFiguraTion

8-LEAD PLASTIC SO

N8 PACKAGE 8-LEAD PDIP

= 150°C, θJA = 130°C/W (N8)

JMAX

= 150°C, θJA = 150°C/W (S8)

JMAX

GND

S8 PACKAGE

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

GND

N PACKAGE

14-LEAD PDIP

= 150°C, θJA = 130°C/W (N)

JMAX

= 150°C, θJA = 150°C/W (S)

JMAX

S PACKAGE

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

For more information www.linear.com/LT1785

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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 speciﬁed with wider operating temperature ranges. *The temperature grade is identiﬁed by a label on the shipping container. For more information on lead free part marking, go to: http://www.linear.com/leadfree/

This product is only offered in trays. For more information go to: http://www.linear.com/packaging/

For more information www.linear.com/LT1785

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LT1785/LT1785A/ LT1791/LT1791A

Dc elecTrical characTerisTics

The l denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C, VCC = 5V.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

OD1

OD2

Differential Driver Output Voltage (Unloaded) IO = 0

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

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

∆|V

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

| Change in Magnitude of Driver Common Mode Output

Voltage for Complementary Output States

∆V

IN1

IN2

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

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

OUT

< 6V

LT1785 –7V ≤ V

RS485 Unit Load 0.25

Driver Short-Circuit Current V

Driver Output Fault Current V

Receiver Short-Circuit Current 0V ≤ V

Driver Three-State Output Current –7V ≤ V

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

R = 27Ω (RS485), Figure 1 R = 18Ω

R = 27Ω or R = 50Ω, Figure 1

= –7V

–60V ≤ V

LT1785A/LT1791A: –7V ≤ V

≤ 60V

RE > 2V or Power Off

– 60V ≤ V

OUT

= 60V

= –60V

–60V ≤ V

≤ 60V

≤ 12V

= HIGH, Force VO = –7V = LOW, Force VO = 12V

≤ V

≤ 12V

≤ 60V

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

≤ 12V

2.0

1.5

1.2

2 2.5 3 V

2 V

l l

–0.15

–6

–0.2

3.5 4 V

–1 1 µA

85 125

4.1 5 V

2.70

2.45

2.2

0.15

–0.08

0.3 0.5 V

125

50 90 kΩ

l l

–6

–0.2

–6

l l l l

5.5

4.5

0.2

0.2 V

0.8 V

5 µA

0.3

mA mA mA

0.2 0

kΩ kΩ

250 250

mA mA

6 mA

±35 mA

0.3 6

9 9 8

0.3

mA mA

mA mA mA mA

V V V

V V

178591fd

For more information www.linear.com/LT1785

Page 5

LT1785/LT1785A/

LT1791/LT1791A

swiTching characTerisTics

The l denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C, VCC = 5V.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

PLH

PHL

SKEW

, t

PLH

PHL

SKD

MAX

SHDN

ZH(SHDN)

ZL(SHDN)

ZH(SHDN)

ZL(SHDN)

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

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

200 800 2000 ns

250 kbps

700 2000 ns

500 3000 ns

800 3000 ns

200 5000 ns

800 5000 ns

400 900 ns

300 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.

178591fd

For more information www.linear.com/LT1785

Page 6

LT1785/LT1785A/

OUTPUT VOLTAGE (V)

DIFFERENTIAL VOLTAGE (V)

3.0

DELAY (ns)

1000

(mA)

700

LT1791/LT1791A

Typical perForMance characTerisTics

Driver Differential Output Voltage vs Load Resistance

TA = 25°C

100 1k

LOAD RESISTANCE (Ω)

Driver Propagation Delay vs Temperature

900

800

700

600

500

400

300

PROPAGATION DELAY (ns)

200

100

–40

–20

TEMPERATURE (°C)

Driver Differential Output Voltage vs Temperature

2.5

2.0

1.5

1.0

0.5

R = 27Ω

178591 G01

–40

–20

TEMPERATURE (°C)

178591 G02

100

LT1791 Driver Output Leakage DE = 0V

1mA/DIV

–60V

178591 G04

100

178591 G05

200µA/DIV

60V

Receiver Propagation Delay vs Temperature

800

600

400

200

–40

–20

PHL

PLH

TEMPERATURE (°C)

LT1791 Receiver Input Current vs V

–60V

178591 G03

178591 G06

100

60V

LT1785 Input Characteristics Pins A or B; DE = RE = 0V

1mA/DIV

–60V

Supply Current vs Temperature

DRIVER AND

RECEIVER ON

RECEIVER ONLY

, V

60V

178591 G07

–40

STANDBY

–20

TEMPERATURE (°C)

178591 G08

100

Receiver Propagation Delay vs Differential Input Voltage

600

500

400

300

DELAY (ns)

LH VCM = 12V

200

100

HL VCM = 12V

VIN DIFFERENTIAL (V)

HL VCM = –7V

LH VCM = –7V

3 4

178591 G09

178591fd

For more information www.linear.com/LT1785

Page 7

pin FuncTions

LT1785/LT1785A/

LT1791/LT1791A

RO: Receiver Output. TTL level logic output. If the receiver is active (RE pin low), RO is high if receiver input A ≥ B by 200mV. If A ≤ B by 200mV, then RO will be low. RO

assumes a high impedance output state when or the part is powered off. RO is protected from output shorts from ground to 6V.

RE: Receiver Output Enable. TTL level logic input. A logic low on RE enables normal operation of the receiver output RO. A logic high level at RE places the receiver output pin RO into a high impedance state. If receiver enable RE and driver enable DE are both in the disable state, the circuit goes to a low power shutdown state. Placing either RE or DE into its active state brings the circuit out of shutdown. Shutdown state is not entered until a 3µs delay after both RE and DE are disabled, allowing for logic skews in tog gling between transmit and receive modes of operation. For CAN bus applications, RE the circuit from entering shutdown.

DE: Driver Output Enable. TTL level logic input. A logic high on DE enables normal operation of the driver out puts (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 state. If receiver enable DE are both in the disable state, the circuit goes to a low power shutdown state. Placing either RE or DE into its active state brings the circuit out of shutdown. Shutdown state is not entered until a 3µs delay after both RE and DE are disabled, allowing for logic skews in toggling between transmit and receive modes of operation. For CAN bus operation the DE pin is used for signal input to place the data bus in dominant or recessive states.

DI: Driver Input. TTL level logic input. A logic high at DI causes driver output A or Y to a high state, and output B or Z to a low state. Complementary output states occur for DI low. For CAN bus applications DI should be tied low.

GND: Ground.

should be tied low to prevent

and driver enable

is high

Y: Driver Output. The Y driver output is in phase with the driver input DI. In the LT1785 driver output Y is internally connected to receiver input A. The driver output assumes a high impedance state when DE is low, power is off or thermal shutdown is activated. The driver output is pro tected from shorts between ±60V in both active and high impedance modes. 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. The driver output is protected from shorts between ±60V in both active and high impedance modes. For CAN applications, output Z is the CANH output node.

A: Receiver Input. The A receiver input forces a high receiver output when V(A) ≥ [V(B) + 200mV]. V(A) ≤ [V(B)– 200mV] forces a receiver output low. Receiver inputs A and B are protected against voltage faults between ±60V. The high input impedance allows up to 128 LT1785 or LT1791 transceivers on one RS485 data bus.

The LT1785A/LT1791A have guaranteed receiver input thresholds –200mV < V guaranteed to be in a high state for 0V inputs.

B: Receiver Input. The B receiver input forces a high receiver output when V(A) ≥ [V(B) + 200mV]. When V(A) ≤ [V(B) – 200mV], the B receiver forces a receiver output low. Receiver inputs A and B are protected against voltage faults between ±60V allows up to 128 LT1785 or LT1791 transceivers on one RS485 data bus.

The LT1785A/LT1791A have guaranteed receiver input thresholds –200mV < VTH < 0. Receiver outputs are guaranteed to be in a high state for 0V inputs.

: Positive Supply Input. For RS422 or RS485 operation,

4.75V ≤ V output drive swing. V low ESR capacitor directly at Pin 8 (V

≤ 5.25V. Higher VCC input voltages increase

< 0. Receiver outputs are

. The high input impedance

should be decoupled with a 0.1µF

For more information www.linear.com/LT1785

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Page 8

LT1785/LT1785A/

LT1791/LT1791A

TesT circuiTs

1785/91 F01

RECEIVER

OUTPUT

TEST POINT

Figure 1. Driver DC Test Load Figure 2. Receiver Timing Test Load

DIFF

15pF

1785/91 F03

OUTPUT

UNDER TEST

500Ω

Figure 3. Driver/Receiver Timing Test Circuit Figure 4. Driver Timing Test Load

1785/91 F02

1785/91 F04

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For more information www.linear.com/LT1785

Page 9

FuncTion Tables

LT1785/LT1785A/

LT1791/LT1791A

LT1785 Transmitting

INPUTS OUTPUTS

RE DE DI A B RO

0 1 0 0 1 0

0 1 1 1 0 1

1 0 X Hi-Z Hi-Z Hi-Z

1 1 0 0 1 Hi-Z

1 1 1 1 0 Hi-Z

LT1785 Receiving

INPUTS OUTPUT

RE DE DI A-B RO

0 0 X ≤ –200mV 0

0 0 X ≥ 200mV* 1

0 0 X Open 1**

1 0 X X Hi-Z

* ≥ 0mV for LT1785A ** 1 for LT1785A; 1 or 0 for LT1785

LT1791

INPUTS OUTPUTS

RE DE DI A-B Y Z RO

0 0 X ≤ –200mV Hi-Z Hi-Z 0

0 0 X ≥ 200mV* Hi-Z Hi-Z 1

0 0 X Open Hi-Z Hi-Z 1**

0 1 0 ≤ –200mV 0 1 0

0 1 0 ≥ 200mV* 0 1 1

0 1 0 Open 0 1 1**

0 1 1 ≤ –200mV 1 0 0

0 1 1 ≥ 200mV* 1 0 1

0 1 1 Open 1 0 1**

1 0 X X Hi-Z Hi-Z Hi-Z

1 1 0 X 0 1 Hi-Z

1 1 1 X 1 0 Hi-Z

* ≥ 0mV for LT1791A ** 1 for LT1791A; 1 or 0 for LT1791

For more information www.linear.com/LT1785

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Page 10

LT1785/LT1785A/

LT1791/LT1791A

swiTching TiMe waVeForMs

A, B

–V

1/2 V

1.5V

10%

f = 125kHz, tr ≤ 10ns, tf ≤ 10ns

PLH

SKEW

90%

DIFF

= V(A) – V(B)

1.5V

1/2 V

PHL

SKEW

90%

10%

1785/91 F05

Figure 5. Driver Propagation Delays

1.5V

f = 125kHz, tr ≤ 10ns, tf ≤ 10ns

ZL(SHDN), tZL

2.3V

OUTPUT NORMALLY LOW

OUTPUT NORMALLY HIGH

ZH(SHDN), tZH

1.5V

0.5V

178591 F06

Figure 6. Driver Enable and Disable Times

A – B

OD2

–V

OD2

PHL

1.5V

f = 125kHz, tr ≤ 10ns, tf ≤ 10ns

0V 0V

OUTPUT

INPUT

PLH

1.5V

178591 F07

Figure 7. Receiver Propagation Delays

1.5V f = 125kHz, tr ≤ 10ns, tf ≤ 10ns

, t

1.5V

ZL(SHDN)

ZH(SHDN)

OUTPUT NORMALLY LOW

OUTPUT NORMALLY HIGH

, t

1.5V

0.5V

178591 F08

Figure 8. Receiver Enable and Disable Times

178591fd

For more information www.linear.com/LT1785

Page 11

applicaTions inForMaTion

LT1785/LT1785A/

LT1791/LT1791A

Overvoltage Protection

The LT1785/LT1791 RS485/RS422 transceivers answer an applications need for overvoltage fault tolerance on data networks. Industrial installations may encounter common mode voltages between nodes far greater than the –7V to 12V range speciﬁed for compliance to RS485 standards. CMOS RS485 transceivers can be damaged by voltages above their absolute maximum ratings of typically –8V to 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 toler ance of CMOS RS485 transceivers makes implementation of effective external protection networks difﬁcult without interfering with proper data network performance within the –7V to 12V region of RS485 operation.

The high overvoltage rating of the LT1785/LT1791 facili tates easy extension to almost any level. Simple discrete component driver output voltages to less than ±60V can be added to the device to extend protection to any desired level. Figure 11 shows a protection network against faults to the120VAC line voltage.

The LT1785/LT1791 protection is achieved by using a high voltage bipolar integrated circuit process for the transceiv ers. The naturally high breakdown voltages of the bipolar process provides protection in powered-off and high impedance current limit design to protect against overvoltage faults while still allowing high current output drive.

ESD Protection

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

networks

conditions.

that limit the receiver input and

The driver outputs use a foldback

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 discharge or ±4kV contact discharge. Due to their very high input impedance, the LT1791 receiver pins are protected to IEC-1000-4-2 level 2, or ±15kV air and ±4kV contact discharges. This level of ESD protection will guarantee immunity from ﬁeld failures in all but the most severe ESD environments. The LT1791 receiver input ESD tolerance may be increased to IEC level 4 compliance by adding 2.2k resistors in series with these pins.

Low Power Shutdown

The LT1785/LT1791 have RE and DE logic inputs to control the receive and transmit modes of the transceivers. The RE input allows normal data reception when in the low state. The receiver output goes to a high impedance state when RE is high, allowing multiplexing the RO data line. The DE logic input performs a similar function on the driver outputs. A high state on DE activates the differential driver outputs, a low state places both driver outputs in to high impedance. Tying the RE and DE logic inputs together may be done to allow one logic signal to toggle the transceiver from receive to transmit modes. The DE input is used as the data input in CAN bus applications.

Disabling both the driver and receiver places the device into a low supply current shutdown mode. An internal time delay of 3µs minimum prevents entering shutdown due to small logic skews when a toggle between receive and transmit is desired. The recovery time from shutdown mode is typically 12µs. The user must be careful to allow for this wake-up delay from shutdown mode. To allow full 250kbaud data rate transmission in CAN applications, the RE pin should be tied low to prevent entering shutdown mode.

For more information www.linear.com/LT1785

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Page 12

LT1785/LT1785A/ LT1791/LT1791A

applicaTions inForMaTion

Slew Limiting for EMI Emissions Control

The LT1785/LT1791 feature controlled driver output slew rates to control high frequency EMI emissions from equip

ment and data cables. The slew limiting limits data rate operation to 250kbaud. Slew limiting also mitigates the adverse affects of imperfect transmission line termina

tion caused by stubs or mismatched cable. In some low speed, short distance networks, cable termination may be eliminated completely with no adverse effect on data transmission.

120Ω

Data Network Cable Selection and Termination

Long distance data networks operating at high data trans

mission rates should use high quality, low attenuation cable with well-matched cable terminations. Short distance networks at low data rates may use much less expensive P

VC cable. These cables have characteristic impedances as low as 72Ω. The LT1785/LT1791 output drivers are guaranteed to drive cables as low as 72Ω.

120Ω

LT1791LT1791

178591 F09

Figure 9. Full-Duplex RS422

178591fd

For more information www.linear.com/LT1785

Page 13

package DescripTion

(0.508)

.400*

NOTE:

1. DIMENSIONS ARE

*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm)

N8 Package

8-Lead PDIP (Narrow 0.300)

(LTC DWG # 05-08-1510)

87 6

.255 ± .015*

(6.477 ± 0.381)

LT1785/LT1785A/

LT1791/LT1791A

(10.160)

MAX

.300 – .325

(7.620 – 8.255)

.065

(1.651)

.008 – .015

(0.203 – 0.381)

+.035

.325

–.015 +0.889

8.255

()

–0.381

INCHES

MILLIMETERS

TYP

.045 – .065

(1.143 – 1.651)

.100

(2.54)

BSC

.130 ± .005

(3.302 ± 0.127)

.120

(3.048)

MIN

.018 ± .003

(0.457 ± 0.076)

.020

MIN

N8 1002

For more information www.linear.com/LT1785

178591fd

Page 14

LT1785/LT1785A/

(0.101 – 0.254)

.189 – .197

.030

MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)

LT1791/LT1791A

package DescripTion

S8 Package

8-Lead Plastic Small Outline (Narrow 0.150)

(LTC DWG # 05-08-1610)

.050 BSC

.245 MIN

±.005

TYP

RECOMMENDED SOLDER PAD LAYOUT

.010 – .020

(0.254 – 0.508)

.008 – .010

(0.203 – 0.254)

NOTE:

1. DIMENSIONS IN

2. DRAWING NOT TO SCALE

3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.

× 45°

.016 – .050

(0.406 – 1.270)

INCHES

(MILLIMETERS)

.045 ±.005

.160

±.005

0°– 8° TYP

.228 – .244

(5.791 – 6.197)

.053 – .069

(1.346 – 1.752)

.014 – .019

(0.355 – 0.483)

TYP

(4.801 – 5.004)

NOTE 3

.150 – .157

(3.810 – 3.988)

NOTE 3

.004 – .010

.050

(1.270)

BSC

SO8 0303

178591fd

For more information www.linear.com/LT1785

Page 15

package DescripTion

(1.651)

.770*

NOTE:

1. DIMENSIONS ARE

*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm)

N Package

14-Lead PDIP (Narrow 0.300)

(LTC DWG # 05-08-1510)

.255 ± .015*

(6.477 ± 0.381)

1213

(19.558)

MAX

LT1785/LT1785A/

LT1791/LT1791A

8910

.300 – .325

(7.620 – 8.255)

(0.508)

.008 – .015

(0.203 – 0.381)

+.035

.325

–.015

+0.889

8.255

()

–0.381

INCHES

MILLIMETERS

.020

MIN

.130 ± .005

(3.302 ± 0.127)

.120

(3.048)

MIN

.005

(0.127)

MIN

(1.143 – 1.651)

.100

(2.54)

BSC

.045 – .065

.065

TYP

.018 ± .003

(0.457 ± 0.076)

N14 1103

For more information www.linear.com/LT1785

178591fd

Page 16

LT1785/LT1785A/

(3.810 – 3.988)

.337 – .344

.030

MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)

LT1791/LT1791A

package DescripTion

S Package

14-Lead Plastic Small Outline (Narrow 0.150)

(LTC DWG # 05-08-1610)

.050 BSC

.245 MIN

123 N/2

±.005

TYP

RECOMMENDED SOLDER PAD LAYOUT

.010 – .020

(0.254 – 0.508)

.008 – .010

(0.203 – 0.254)

NOTE:

1. DIMENSIONS IN

2. DRAWING NOT TO SCALE

3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.

× 45°

.016 – .050

(0.406 – 1.270)

INCHES

(MILLIMETERS)

.045 ±.005

±.005

.160

0° – 8° TYP

.228 – .244

(5.791 – 6.197)

.053 – .069

(1.346 – 1.752)

.014 – .019

(0.355 – 0.483)

TYP

(8.560 – 8.738)

NOTE 3

11 10

.050

(1.270)

BSC

.150 – .157

N/2

NOTE 3

.004 – .010

(0.101 – 0.254)

S14 0502

178591fd

For more information www.linear.com/LT1785

Page 17

LT1785/LT1785A/

LT1791/LT1791A

reVision hisTory

REV DATE DESCRIPTION PAGE NUMBER

D 03/15 Added notes to Function Tables 9

(Revision history begins at Rev D)

Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

For more information www.linear.com/LT1785

178591fd

Page 18

LT1785/LT1785A/

RAYCHEM

LT1791/LT1791A

Typical applicaTion

LT1785

120Ω

LT1785

120Ω

LT1785

178591 F10

Figure 10. Half-Duplex RS485 Network Operation

POLYSWITCH

TR600-150

× 2

COMPOSITE

47Ω

CARBON

0.1µF 300V

RT,120Ω

178591 F11

LT1785

1.5KE36CA

Figure 11. RS485 Network with 120V AC Line Fault Protection

relaTeD parTs

PART NUMBER DESCRIPTION COMMENTS

LTC2854/LTC2855 3.3V 20Mbps RS485/RS422 Transceivers with Integrated

Switchable Termination

LTC2856/LTC2857/ LTC2858

LTC2850/LTC2851/

5V 20Mbps and Slew Rate Limited 15kV RS485/RS422 Transceivers

3.3V 20Mbps RS485/RS422 Transceivers ±15kV ESD, 125°C Operation

LTC2852

LTC2859/LTC2861 20Mbps RS485 Transceivers with Integrated Switchable

Termination

LTC2862/LTC2863/

±60V Fault Protected 3V to 5.5V RS485/RS422 Transceivers 20Mbps or 250kbps, ±15kV HBM ESD, ±25V Common Mode

LTC2864/LTC2865

LTM2881 Complete 3.3V Isolated RS485/RS422 µModule

Transceiver

+ Power

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507

For more information www.linear.com/LT1785

●

www.linear.com/LT1785

Up to ±25kV HBM ESD, 125°C Operation

±15kV ESD, 125°C Operation

Integrated, Switchable,120Ω Termination Resistor, ±15kV ESD

Range

2500V

Isolation with Integrated Isolated DC/DC Converter and

RMS

Switchable Termination

178591fd

LT 0315 REV D • PRINTED IN USA

 LINEAR TECHNOLOGY CORPORATION 1998

ANALOG DEVICES LT 1785 IS8 Datasheet

Specifications and Main Features

Frequently Asked Questions

User Manual

DescripTion

Typical applicaTion

absoluTe MaxiMuM raTings

pin conFiguraTion

applicaTions inForMaTion

package DescripTion

Typical applicaTion

relaTeD parTs