Datasheet

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LTC485

485fk

For more information www.linear.com/LTC485

TYPICAL APPLICATION

DESCRIPTION

Low Power RS485

Interface Transceiver

The LT C

485 is a low power differential bus/line trans-

ceiver designed for multipoint data transmission standard

RS485 applications with extended common mode range

(12V to –7V). It also meets the requirements of RS422.

The CMOS design offers significant power savings over

its bipolar counterpart without sacrificing ruggedness

against overload or ESD damage.

The driver and receiver feature three-state outputs, with

the driver outputs maintaining high impedance over the

entire common mode range. Excessive power dissipa

tion caused by bus contention or faults is prevented by a

thermal shutdown cir

cuit which for

ces the driver outputs

into a high impedance state.

The receiver has a fail-safe feature which guarantees a

high output state when the inputs are left open.

The LTC485 is fully specified over the commercial and

extended industrial temperature range.

Driver Outputs

FEATURES

APPLICATIONS

Low Power: I

= 300μA Typ

Designed for RS485 Interface Applications

Single 5V Supply

–7V to 12V Bus Common Mode Range Permits

±7V Ground Difference Between Devices on the Bus

Thermal Shutdown Protection

Power-Up/Down Glitch-Free Driver Outputs

Permit Live Insertion or Removal of Transceiver

Driver Maintains High Impedance in Three-State

or with the Power Off

Combined Impedance of a Driver Output and

Receiver Allows Up to 32 Transceivers on the Bus

(C- and I-Grades)

70mV Typical Input Hysteresis

30ns Typical Driver Propagation Delays

with 5ns Skew for Up to 2.5MB Operation

Pin Compatible with ±60V Protected LTC2862

Low Power RS485/RS422 Transceiver

Level Translator

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

CC1

GND1

RO1

RE1

DE1

DI1

CC2

GND2

RO2

RE2

DE2

DI2

485 TA01a

485 TA01b

Summary of content (14 pages)

PAGE 1
LTC485 Low Power RS485 Interface Transceiver FEATURES n n n n n n n n n n n DESCRIPTION Low Power: ICC = 300μA Typ Designed for RS485 Interface Applications Single 5V Supply –7V to 12V Bus Common Mode Range Permits ±7V Ground Difference Between Devices on the Bus Thermal Shutdown Protection Power-Up/Down Glitch-Free Driver Outputs Permit Live Insertion or Removal of Transceiver Driver Maintains High Impedance in Three-State or with the Power Off Combined Impedance of a Driver Output and Receiver Allo
PAGE 2
LTC485 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) TOP VIEW Supply Voltage...........................................................12V Control Input Voltages......................–0.5V to VCC + 0.5V Driver Input Voltage..........................–0.5V to VCC + 0.5V Driver Output Voltage...............................................±14V Receiver Input Voltage.............................................±14V Receiver Output Voltages................. –0.5V to VCC + 0.
PAGE 3
LTC485 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V ±5%, unless otherwise noted. (Notes 2 and 3) SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS VIL Input Low Voltage DE, DI, RE l 0.8 V IIN1 Input Current DE, DI, RE l ±2 μA IIN2 Input Current (A, B) DE = 0, VCC = 0V or 5.25V C-, I-Grade VIN = 12V VIN = –7V l l 1 –0.8 mA mA M-Grade VIN = 12V VIN = –7V l l 2 –1.
PAGE 4
LTC485 TYPICAL PERFORMANCE CHARACTERISTICS Receiver Output Low Voltage vs Output Current –18 TA = 25°C 32 OUTPUT CURRENT (mA) OUTPUT CURRENT (mA) 24 20 16 12 8 4 0 0.5 0 4.4 –12 –10 –8 –6 3.2 4 3 OUTPUT VOLTAGE (V) 5 0.5 0.4 0.3 0.2 2.4 TA = 25°C 56 48 40 32 24 16 0 125 0 1 1.8 1.7 40 30 20 10 485 G07 25 50 0 75 TEMPERATURE (°C) 100 1.64 TA = 25°C –84 –72 –60 –48 –36 –24 0 125 TTL Input Threshold vs Temperature –12 4 –25 485 G06 1.
PAGE 5
LTC485 TYPICAL PERFORMANCE CHARACTERISTICS Driver Skew vs Temperature Supply Current vs Temperature 5.4 640 7.0 4.8 580 6.5 4.2 520 6.0 3.6 5.5 5.0 3.0 2.4 4.5 1.8 4.0 1.2 3.5 0.6 3.0 –50 –25 25 50 0 75 TEMPERATURE (°C) 100 125 SUPPLY CURRENT (µA) 7.
PAGE 6
LTC485 TEST CIRCUITS A R RECEIVER OUTPUT VOD CRL 15pF VOC R S1 TEST POINT 1k 1k VCC S2 485 F02 B 485 F01 Figure 1. Driver DC Test Load Figure 2. Receiver Timing Test Load 3V DE A DI CL1 RDIFF B CL2 A S1 RO B RE VCC 500Ω OUTPUT UNDER TEST S2 15pF CL 485 F04 485 F03 Figure 3. Driver/Receiver Timing Test Circuit Figure 4. Driver Timing Test Load #2 SWITCHING TIME WAVEFORMS 3V 1.5V DI f = 1MHz, tr ≤ 10ns, tf ≤ 10ns 0V tPLH B A VO 0V –VO 1.
PAGE 7
LTC485 SWITCHING TIME WAVEFORMS 3V 1.5V DI tLZ tZL 5V A, B 2.3V OUTPUT NORMALLY LOW 0.5V 2.3V OUTPUT NORMALLY HIGH 0.5V VOL A, B 1.5V f = 1MHz, tr ≤ 10ns, tf ≤ 10ns 0V VOH 0V tHZ tZH 485 F06 Figure 6. Driver Enable and Disable Times R VOH 1.5V VOL f = 1MHz, tr ≤ 10ns, tf ≤ 10ns tPHL VOD2 A, B –VOD2 0V 1.5V OUTPUT tPLH INPUT 485 F07 Figure 7. Receiver Propagation Delays 3V 1.5V RE R tLZ tZL 5V R 0V 1.5V f = 1MHz, tr ≤ 10ns, tf ≤ 10ns 0V 1.
PAGE 8
LTC485 APPLICATIONS INFORMATION Basic Theory of Operation Previous RS485 transceivers have been designed using bipolar technology because the common mode range of the device must extend beyond the supplies and the device must be immune to ESD damage and latchup. Unfortunately, the bipolar devices draw a large amount of supply current, which is unacceptable for the numerous applications that require low power consumption.
PAGE 9
LTC485 APPLICATIONS INFORMATION The LTC485 output stage will maintain a high impedance state until the breakdown of the N-channel or P-channel is reached when going positive or negative respectively. The output will be clamped to either VCC or ground by a Zener voltage plus a Schottky diode drop, but this voltage is way beyond the RS485 operating range. This clamp protects the MOS gates from ESD voltages well over 2000V.
PAGE 10
LTC485 APPLICATIONS INFORMATION LTC485 Line Length vs Data Rate The maximum line length allowable for the RS422/RS485 standard is 4000 feet. Figures 17 and 18 show that the LTC485 is able to comfortably drive 4000 feet of wire at 110kHz. 100Ω C A LTC485 LTC485 D B NOISE GENERATOR TTL IN RO TTL OUT COMMON MODE VOLTAGE (A + B)/2 4000 FT 26AWG TWISTED PAIR DI 485 F14 Figure 14. Line Length Test Circuit 485 F17 Figure 17.
PAGE 11
LTC485 TYPICAL APPLICATION Typical RS485 Network Rt Rt 485 TA02 PACKAGE DESCRIPTION J8 Package 8-Lead CERDIP (Narrow .300 Inch, Hermetic) (Reference LTC DWG # 05-08-1110) CORNER LEADS OPTION (4 PLCS) .023 – .045 (0.584 – 1.143) HALF LEAD OPTION .045 – .068 (1.143 – 1.650) FULL LEAD OPTION .005 (0.127) MIN .405 (10.287) MAX 8 7 6 5 .025 (0.635) RAD TYP .220 – .310 (5.588 – 7.874) 1 .300 BSC (7.62 BSC) 2 3 4 .200 (5.080) MAX .015 – .060 (0.381 – 1.524) .008 – .018 (0.203 – 0.
PAGE 12
LTC485 PACKAGE DESCRIPTION N Package 8-Lead PDIP (Narrow .300 Inch) (Reference LTC DWG # 05-08-1510 Rev I) .300 – .325 (7.620 – 8.255) ( +.035 .325 –.015 8.255 +0.889 –0.381 .130 ±.005 (3.302 ±0.127) .045 – .065 (1.143 – 1.651) .065 (1.651) TYP .008 – .015 (0.203 – 0.381) ) .400* (10.160) MAX 8 7 6 5 1 2 3 4 .255 ±.015* (6.477 ±0.381) .120 (3.048) .020 MIN (0.508) MIN .018 ±.003 .100 (2.54) BSC (0.457 ±0.076) N8 REV I 0711 NOTE: 1.
PAGE 13
LTC485 REVISION HISTORY (Revision history begins at Rev I) REV DATE DESCRIPTION PAGE NUMBER I 4/11 Removed lead free version of LTC485MJ8 from Order Information section. J 01/14 Modified to account for high temperature leakage in M-grade K 02/14 Remove tape and reel option for DIP package in Order Information section. 2 1, 3 2 485fk Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use.
PAGE 14
LTC485 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC486/LTC487 Low Power Quad RS485 Drivers 110μA Supply Current LTC488/LTC489 Low Power Quad RS485 Receivers 7mA Supply Current LTC490/LTC491 Low Power Full-Duplex RS485 Transceivers 300μA Supply Current LTC1480 3.