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LT1785/LT1785A/

LT1791/LT1791A

Rev. F

For more information www.analog.com

TYPICAL APPLICATION

DESCRIPTION

60V Fault Protected

RS485/RS422 Transceivers

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 over

voltage 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 out

putscontrol EMI emissions and improve data transmis-

sion 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.

Normal Operation Waveforms at 250kBaud

FEATURES

APPLICATIONS

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

AEC-Q100 Qualiﬁed for Automotive Applications

(LT1785#W)

Industrial Control Data Networks

CAN Bus Applications

HVAC Controls

GND1

GND2

TERM

178591 TA01

RO1

RE1

DE1

DI1

LT1785

RO2

RE2

DE2

DI2

LT1785

CC1

CC2

TERM

178591 TA02

Y-Z

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Summary of content (18 pages)

PAGE 1
LT1785/LT1785A/ LT1791/LT1791A 60V Fault Protected RS485/RS422 Transceivers FEATURES n n n n n n n n n n n n DESCRIPTION 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 n IEC-1000-4-2 Level 4: ±15kV Air Discharge n 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/
PAGE 2
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..........
PAGE 3
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
PAGE 4
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.
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.
PAGE 6
LT1785/LT1785A/ LT1791/LT1791A TYPICAL PERFORMANCE CHARACTERISTICS Driver Differential Output Voltage vs Load Resistance Driver Differential Output Voltage vs Temperature 3.0 4 2 1 100 LOAD RESISTANCE (Ω) 10 2.5 2.0 1.5 600 tPLH 400 1.0 200 0.
PAGE 7
LT1785/LT1785A/ LT1791/LT1791A PIN FUNCTIONS 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 RE is high 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.
PAGE 8
LT1785/LT1785A/ LT1791/LT1791A TEST CIRCUITS A R VOD R S1 TEST POINT RECEIVER OUTPUT VOC 1k CRL 1k VCC S2 B 1785/91 F02 1785/91 F01 Figure 1. Driver DC Test Load Figure 2. Receiver Timing Test Load 5V DE DI A CL1 RDIFF B CL2 A S1 RO B RE 15pF OUTPUT UNDER TEST VCC 500Ω CL S2 1785/91 F04 1785/91 F03 Figure 3. Driver/Receiver Timing Test Circuit Figure 4. Driver Timing Test Load Rev. F 8 For more information www.analog.
PAGE 9
LT1785/LT1785A/ LT1791/LT1791A FUNCTION TABLES LT1785 Transmitting LT1791 INPUTS OUTPUTS INPUTS OUTPUTS RE DE DI A B RO 0 1 0 0 1 0 0 0 X ≤ –200mV Hi-Z Hi-Z 0 0 1 1 1 0 1 0 0 X ≥ 200mV* Hi-Z Hi-Z 1 1 0 X Hi-Z Hi-Z Hi-Z 0 0 X Open Hi-Z Hi-Z 1** 1 1 0 0 1 Hi-Z 0 1 0 ≤ –200mV 0 1 0 1 1 1 1 0 Hi-Z LT1785 Receiving INPUTS OUTPUT RE DE DI A-B Y Z RO 0 1 0 ≥ 200mV* 0 1 1 0 1 0 Open 0 1 1** 0 1 1 ≤ –200mV 1 0 0 0 1
PAGE 10
LT1785/LT1785A/ LT1791/LT1791A SWITCHING TIME WAVEFORMS 5V f = 125kHz, tr ≤ 10ns, tf ≤ 10ns 1.5V DI 1.5V 0V tPLH B A VO 0V –VO 1/2 VO tPHL VO tSKEW 1/2 VO tSKEW 90% 10% 90% 10% VDIFF = V(A) – V(B) tr tf 1785/91 F05 Figure 5. Driver Propagation Delays 5V f = 125kHz, tr ≤ 10ns, tf ≤ 10ns 1.5V DE 1.5V 0V A, B 2.3V OUTPUT NORMALLY LOW 0.5V 2.3V OUTPUT NORMALLY HIGH 0.5V VOL A, B tLZ tZL(SHDN), tZL 5V VOH 0V tHZ tZH(SHDN), tZH 178591 F06 Figure 6.
PAGE 11
LT1785/LT1785A/ LT1791/LT1791A APPLICATIONS INFORMATION 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.
PAGE 12
LT1785/LT1785A/ LT1791/LT1791A APPLICATIONS INFORMATION Slew Limiting for EMI Emissions Control Data Network Cable Selection and Termination The LT1785/LT1791 feature controlled driver output slew rates to control high frequency EMI emissions from equipment and data cables. The slew limiting limits data rate operation to 250kbaud. Slew limiting also mitigates the adverse affects of imperfect transmission line termination caused by stubs or mismatched cable.
PAGE 13
LT1785/LT1785A/ LT1791/LT1791A PACKAGE DESCRIPTION N Package 8-Lead PDIP (Narrow .300 Inch) (Reference LTC DWG # 05-08-1510 Rev I) .400* (10.160) MAX 8 7 6 5 1 2 3 4 .255 ±.015* (6.477 ±0.381) .300 – .325 (7.620 – 8.255) .008 – .015 (0.203 – 0.381) ( +.035 .325 –.015 8.255 +0.889 –0.381 ) .045 – .065 (1.143 – 1.651) .065 (1.651) TYP .100 (2.54) BSC .130 ±.005 (3.302 ±0.127) .120 (3.048) .020 MIN (0.508) MIN .018 ±.003 (0.457 ±0.076) N8 REV I 0711 NOTE: 1.
PAGE 14
LT1785/LT1785A/ LT1791/LT1791A PACKAGE DESCRIPTION S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610 Rev G) .050 BSC .189 – .197 (4.801 – 5.004) NOTE 3 .045 ±.005 8 .245 MIN .160 ±.005 .010 – .020 × 45° (0.254 – 0.508) NOTE: 1. DIMENSIONS IN 5 .150 – .157 (3.810 – 3.988) NOTE 3 1 RECOMMENDED SOLDER PAD LAYOUT .053 – .069 (1.346 – 1.752) 0°– 8° TYP .016 – .050 (0.406 – 1.270) 6 .228 – .244 (5.791 – 6.197) .030 ±.005 TYP .008 – .010 (0.203 – 0.
PAGE 15
LT1785/LT1785A/ LT1791/LT1791A PACKAGE DESCRIPTION N Package 14-Lead PDIP (Narrow .300 Inch) (Reference LTC DWG # 05-08-1510 Rev I) .770* (19.558) MAX 14 13 12 11 10 9 8 1 2 3 4 5 6 7 .255 ±.015* (6.477 ±0.381) .300 – .325 (7.620 – 8.255) .008 – .015 (0.203 – 0.381) ( +.035 .325 –.015 +0.889 8.255 –0.381 NOTE: 1. DIMENSIONS ARE ) .045 – .065 (1.143 – 1.651) .130 ±.005 (3.302 ±0.127) .020 (0.508) MIN .065 (1.651) TYP .120 (3.048) MIN .005 (0.127) .100 MIN (2.54) BSC .018 ±.003 (0.
PAGE 16
LT1785/LT1785A/ LT1791/LT1791A PACKAGE DESCRIPTION S Package 14-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610 Rev G) .337 – .344 (8.560 – 8.738) NOTE 3 .045 ±.005 .050 BSC 14 N 12 11 10 9 8 N .245 MIN .160 ±.005 .228 – .244 (5.791 – 6.197) 1 .030 ±.005 TYP 13 2 3 N/2 N/2 RECOMMENDED SOLDER PAD LAYOUT 1 .010 – .020 × 45 (0.254 – 0.508) .008 – .010 (0.203 – 0.254) 2 3 4 5 .053 – .069 (1.346 – 1.752) NOTE: 1. DIMENSIONS IN .014 – .019 (0.355 – 0.
PAGE 17
LT1785/LT1785A/ LT1791/LT1791A REVISION HISTORY (Revision history begins at Rev D) REV DATE DESCRIPTION D 03/15 Added notes to Function Tables E 12/19 F 03/20 Added Auto Grade PAGE NUMBER 9 1, 3 Removed lead based finish part options 3 Added Auto Grade for H temp range 3 Rev. F Information furnished by Analog Devices is believed to be accurate and reliable.
PAGE 18
LT1785/LT1785A/ LT1791/LT1791A TYPICAL APPLICATION RO RE DE DI 1 RX 2 3 4 RT 120Ω B 7 LT1785 RT 120Ω A 6 6 A TX 6 A 7 B 7 B RX 6 A LT1785 1 2 7 B TX 3 4 RO RE DE DI 178591 F10 LT1785 4 3 DI DE LT1785 2 RE 4 1 DI RO 3 DE 2 RE 1 RO Figure 10. Half-Duplex RS485 Network Operation 8 RO RE DE DI 1 RX 2 3 4 LT1785 TX RAYCHEM POLYSWITCH TR600-150 ×2 47Ω VCC B 7 RT,120Ω A 6 47Ω CARBON COMPOSITE 5W 5 0.1µF 300V 178591 F11 1.5KE36CA Figure 11.