Datasheet

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LTC487

487fc

Typical applicaTion

DescripTion

Quad Low Power

RS485 Driver

The LTC

487 is a low power differential bus/line driver

designed for multipoint data transmission standard RS485

applications with extended common mode range (–7V to

12V). It also meets RS422 requirements.

The CMOS design offers significant power savings over

its bipolar counterpart without sacrificing ruggedness

against overload or ESD damage.

The driver features three-state outputs, with the driver

outputs maintaining high impedance over the entire com-

mon mode range. Excessive power dissipation caused

by bus contention or faults is prevented by a thermal

shutdown circuit which forces the driver outputs into a

high impedance state.

Both AC and DC specifications are guaranteed from 0°C to

70°C (Commercial), –40°C to 85°C (Industrial) and over

the 4.75V to 5.25V supply voltage range.

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.

FeaTures

applicaTions

Very Low Power: I

= 110µA Typ

Designed for RS485 or RS422 Applications

Single 5V Supply

–7V to 12V Bus Common Mode Range Permits ±7V

GND Difference Between Devices on the Bus

Thermal Shutdown Protection

Power-Up/Down Glitch-Free Driver Outputs Permit

Live Insertion/Removal of Package

Driver Maintains High Impedance in Three-State or

with the Power Off

28ns Typical Driver Propagation Delays with

5ns Skew

Pin Compatible with the SN75174, DS96174,

µA96174, and DS96F174

Low Power RS485/RS422 Drivers

Level Translator

DRIVER

LTC487 TA01

RECEIVER

EN 12

1/4 LTC487

120Ω 120Ω

EN 12

1/4 LTC489

4000 FT BELDEN 9841

DATA RATE (bps)

10k

CABLE LENGTH (FT)

100

10k

100k 1M 10M

LTC487 TA09

2.5M

RS485 Cable Length Specification*

* APPLIES FOR 24 GAUGE, POLYETHYLENE

DIELECTRIC TWISTED PAIR

Summary of content (12 pages)

PAGE 1
LTC487 Quad Low Power RS485 Driver Features n n n n n n n n n Description Very Low Power: ICC = 110µA Typ Designed for RS485 or RS422 Applications Single 5V Supply – 7V to 12V Bus Common Mode Range Permits ±7V GND Difference Between Devices on the Bus Thermal Shutdown Protection Power-Up/Down Glitch-Free Driver Outputs Permit Live Insertion/Removal of Package Driver Maintains High Impedance in Three-State or with the Power Off 28ns Typical Driver Propagation Delays with 5ns Skew Pin Compatible with th
PAGE 2
LTC487 Absolute Maximum Ratings Pin Configuration (Note 1) TOP VIEW Supply Voltage (VCC).................................................12V Control Input Voltages..................... –0.5V to VCC + 0.5V Driver Input Voltages....................... –0.5V to VCC + 0.5V Driver Output Voltages............................................. ±14V Control Input Currents..........................................±25mA Driver Input Currents............................................
PAGE 3
LTC487 DC Electrical Characteristics (Industrial) (Notes 2, 3) VCC = 5V ± 5%, 0°C ≤ TA ≤ 70°C (Commercial), –40°C ≤ TA ≤ 85°C SYMBOL PARAMETER CONDITIONS VOD1 Differential Driver Output Voltage (Unloaded) IO = 0 VOD2 Differential Driver Output Voltage (With Load) R = 50Ω; (RS422) Change in Magnitude of Driver Differential Output Voltage for Complementary Output States VOC Driver Common Mode Output Voltage VOC  Change in Magnitude of Driver Common Mode Output Voltage for Complementary Output
PAGE 4
LTC487 Typical Performance Characteristics Driver Output High Voltage vs Output Current TA = 25°C –48 –24 0 1 2 3 32 16 0 4 OUTPUT VOLTAGE (V) 48 2 3 1.63 5.0 1.61 4.0 1.59 1.57 50 TEMPERATURE (°C ) 40 20 0 4 1 2 3 4 OUTPUT VOLTAGE (V) 487 G03 Supply Current vs Temperature 130 3.0 1.0 –50 100 0 487 G02 2.0 0 60 Driver Skew vs Temperature TIME (ns) INPUT THRESHOLD VOLTAGE (V) 1 OUTPUT VOLTAGE (V) 487 G01 TTL Input Threshold vs Temperature 1.
PAGE 5
LTC487 Pin Functions DI1 (Pin 1): Driver 1 Input. If Driver 1 is enabled, then a low on DI1 forces the driver outputs DO1A low and DO1B high. A high on DI1 with the driver outputs enabled will force DO1A high and DO1B low. GND (Pin 8): GND Connection. DO1A (Pin 2): Driver 1 Output. DO3B (Pin 11): Driver 3 Output. DO1B (Pin 3): Driver 1 Output. EN34 (Pin 12): Driver 3 and 4 Outputs Enabled. See Function Table for details. EN12 (Pin 4): Driver 1 and 2 Outputs Enabled. See Function Table for details.
PAGE 6
LTC487 Test Circuit EN12 A S1 R A VOD R B DI VOC DRIVER 1 VCC CL1 500Ω OUTPUT UNDER TEST RDIFF B LTC487 TA02 CL S2 CL2 LTC487 TA04 LTC487 TA03 Figure 3. Driver DC Test Load Figure 4. Driver Timing Test Circuit Figure 5. Driver Timing Test Load #2 Applications Information Typical Application A typical connection of the LTC487 is shown in Figure 6. A twisted pair of wires connect up to 32 drivers and receivers for half duplex data transmission.
PAGE 7
LTC487 Applications Information Losses in a transmission line are a complex combination of DC conductor loss, AC losses (skin effect), leakage, and AC losses in the dielectric. In good polyethylene cables such as the Belden 9841, the conductor losses and dielectric losses are of the same order of magnitude, leading to relatively low overall loss (Figure 7). LOSS PER 100 FT (dB) 10 1.0 Cable Termination The proper termination of the cable is very important.
PAGE 8
LTC487 Applications Information AC Cable Termination Cable termination resistors are necessary to prevent unwanted reflections, but they consume power. The typical differential output voltage of the driver is 2V when the cable is terminated with two 120Ω resistors, causing 33mA of DC current to flow in the cable when no data is being sent. This DC current is about 220 times greater than the supply current of the LTC487.
PAGE 9
LTC487 Applications Information A TransZorb is a silicon transient voltage suppressor that has exceptional surge handling capabilities, fast response time, and low series resistance. They are available from General Semiconductor Industries and come in a variety of breakdown voltages and prices. Be sure to pick a breakdown voltage higher than the common mode voltage required for your application (typically 12V). Also, don’t forget to check how much the added parasitic capacitance will load down the bus.
PAGE 10
LTC487 Package Description SW Package 16-Lead Plastic Small Outline (Wide .300 Inch) (Reference LTC DWG # 05-08-1620) .050 BSC .045 ±.005 .030 ±.005 TYP .398 – .413 (10.109 – 10.490) NOTE 4 16 N 15 14 13 12 11 10 9 N .325 ±.005 .420 MIN .394 – .419 (10.007 – 10.643) NOTE 3 1 2 3 N/2 N/2 RECOMMENDED SOLDER PAD LAYOUT 1 .005 (0.127) RAD MIN .009 – .013 (0.229 – 0.330) NOTE: 1. DIMENSIONS IN .291 – .299 (7.391 – 7.595) NOTE 4 .010 – .029 × 45° (0.254 – 0.737) 2 3 4 5 6 .093 – .
PAGE 11
LTC487 Revision History (Revision history begins at Rev C) REV DATE DESCRIPTION PAGE NUMBER C 8/10 Reversed temperature ranges for LTC487CSW#PBF and LTC487IN#PBF. 2 487fc 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.
PAGE 12
LTC487 Typical Application RS232 to RS485 Level Translator with Hysteresis R = 220k Y 10k RS232 IN DRIVER 5.6k 1/4 LTC487 120Ω Z 19k ¦VY - VZ ¦ HYSTERESIS = 10kΩ • ———— ≈ ———— R R LTC487 TA14 487fc 12 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.