LTC485C [Linear]

Low Power RS485 Interface Transceiver; 低功率RS485接口收发器


型号：	LTC485C
厂家：	Linear
描述：	Low Power RS485 Interface Transceiver 低功率RS485接口收发器
文件：	总12页 (文件大小：329K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

LTC485

Low Power RS485

Interface Transceiver

DESCRIPTIO

EATURE

■

Low Power: I_CC= 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

70mV Typical Input Hysteresis

30ns Typical Driver Propagation Delays

with 5ns Skew

Pin Compatible with the SN75176A, DS75176A

and µA96176

TheLTC485isalowpowerdifferentialbus/linetransceiver

designedformultipointdatatransmissionstandardRS485

applications with extended common-mode range (12V to

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

TheCMOSdesignofferssignificantpowersavingsoverits

bipolarcounterpartwithoutsacrificingruggednessagainst

overload of 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 dissipation

caused by bus contention or faults is prevented by a

thermal shutdown circuit which forces 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.

O U

PPLICATI

■

Low Power RS485/RS422 Transceiver

Level Translator

■

TYPICAL APPLICATI

Driver Outputs

RO1

RE1

DE1

DI1

CC1

GND1

RO2

RE2

DE2

DI2

CC2

GND2

LTC485 • TA01

LTC485 • TA02

LTC485

W W W

ABSOLUTE AXI U RATI GS

(Note 1)

PACKAGE RDER I FOR ATIO

ORDER PART

Supply Voltage ....................................................... 12V

Control Input Voltages ................... –0.5V to V_CC+ 0.5V

Driver Input Voltage....................... –0.5V to V_CC+ 0.5V

Driver Output Voltage ........................................... ±14V

Receiver Input Voltage.......................................... ±14V

Receiver Output Voltages .............. –0.5V to V_CC+ 0.5V

Operating Temperature Range

LTC485I...................................... –40°C ≤ T_A≤ 85°C

LTC485C.......................................... 0°C ≤ T_A≤ 70°C

LTC485M.................................. –55°C ≤ T_A≤ 125°C

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

TOP VIEW

NUMBER

LTC485CJ8

LTC485CN8

LTC485CS8

LTC485IN8

LTC485IS8

LTC485MJ8

GND

J8 PACKAGE

N8 PACKAGE

8-LEAD CERAMIC DIP 8-LEAD PLASTIC DIP

S8 PACKAGE

8-LEAD PLASTIC SOIC

S8 PART MARKING

T_JMAX= 155°C, θ_JA= 100°C/ W (J)

T_JMAX= 100°C, θ_JA= 130°C/ W (N)

_JMAX= 100°C, θ_JA= 170°C/ W (S)

485

485I

V_CC= 5V ±5%, unless otherwise noted. (Notes 2 and 3)

ELECTRICAL CHARACTERISTICS

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

OD1

OD2

Differential Driver Output Voltage (Unloaded)

Differential Driver Output Voltage (with Load)

I = 0

●

R = 50Ω (RS422)

R = 27Ω (RS485), Figure 1

●

1.5

∆V

Change in Magnitude of Driver

DifferentialOutput Voltage for

Complementary States

R = 27Ω or R = 50Ω, Figure 1

●

0.2

Driver Common-Mode Output Voltage

R = 27Ω or R = 50Ω, Figure 1

●

∆ V

Change in Magnitude of Driver

Common-Mode Output Voltage

for Complementary States

0.2

Input High Voltage

Input Low Voltage

Input Current

DE, DI, RE

●

0.8

±2

µA

IN1

IN2

Input Current (A, B)

DE = 0, V = 0V

= 12V

= –7V

±1

or 5.25V

–0.8

0.2

Differential Input Threshold Voltage

for Receiver

–7V ≤ V ≤ 12V

–0.2

3.5

∆V

Receiver Input Hysteresis

Receiver Output High Voltage

Receiver Outpu Low Voltage

= 0V

●

I = –4mA, V = 200mV

O ID

I = 4mA, V = –200mV

0.4

Three-State (High Impedance) Output

Current at Receiver

= Max, 0.4V ≤ V ≤ 2.4V

±1

µA

OZR

Receiver Input Resistance

Supply Current

–7V ≤ V ≤ 12V

●

kΩ

µA

No Load, Pins 2, Outputs Enabled

3, 4 = 0V or 5V

500

300

100

900

500

250

Outputs Disabled

µA

Driver Short-Circuit Current, V

Receiver Short-Circuit Current

= HIGH

= LOW

V = –7V

OSD1

OSD2

OSR

OUT

V = 10V

OUT

0V ≤ V ≤ V

LTC485

SWITCHI G CHARACTERISTICS ^V_CC= 5V ±5%, unless otherwise noted. (Notes 2 and 3)

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Driver Input to Output

DIFF

= 54Ω, C = C = 100pF,

●

PLH

(Figures 3 and 5)

Driver Input to Output

PHL

Driver Output to Output

Driver Rise or Fall Time

Driver Enable to Output High

Driver Enable to Output Low

Driver Disable Time from Low

Driver Disable Time from High

Receiver Input to Output

SKEW

t , t

C = 100pF (Figures 4 and 6) S2 Closed

C = 100pF (Figures 4 and 6) S1 Closed

C = 15pF (Figures 4 and 6) S1 Closed

C = 15pF (Figures 4 and 6) S2 Closed

DIFF

= 54Ω, C = C = 100pF,

200

PLH

PHL

SKD

(Figures 3 and 7)

– t

Differential Receiver Skew

PHL

PLH

Receiver Enable to Output Low

Receiver Enable to Output High

Receiver Disable from Low

Receiver Disable from High

= 15pF (Figures 2 and 8) S1 Closed

= 15pF (Figures 2 and 8) S2 Closed

= 15pF (Figures 2 and 8) S1 Closed

= 15pF (Figures 2 and 8) S2 Closed

The

●

denotes specifications which apply over the full operating

Note 3: All typicals are given for V = 5V and T = 25°C.

CC A

temperature range.

Note 1: Absolute maximum ratings are those beyond which the safety of

the device cannot be guaranteed.

Note 4: The LTC485 is guaranteed by design to be functional over a supply

voltage range of 5V ±10%. Data sheet parameters are guaranteed over the

tested supply voltage range of 5V ±5%.

Note 2: All currents into device pins are positive; all currents out ot device

pins are negative. All voltages are referenced to device ground unless

otherwise specified.

TEST CIRCUITS

TEST POINT

RECEIVER

OUTPUT

15pF

LTC485 • F02

LTC485 • F01

Figure 1. Driver DC Test Load

Figure 2. Receiver Timing Test Load

500Ω

OUTPUT

UNDER TEST

DIFF

15pF

LTC485 • F02

LTC485 • F03

Figure 3. Driver/Receiver Timing Test Circuit

Figure 4. Driver Timing Test Load #2

LTC485

SWITCHI G TI E WAVEFOR S

1.5V

f = 1MHz, t ≤ 10ns, t ≤ 10ns

1.5V

1/2 V

PLH

SKEW

1/2 V

SKEW

90%

20%

80%

= V(A) – V(B)

DIFF

10%

–V

LTC485 • F05

Figure 5. Driver Propagation Delays

1.5V

f = 1MHz, t ≤ 10ns, t ≤ 10ns

1.5V

A, B

2.3V

OUTPUT NORMALLY LOW

OUTPUT NORMALLY HIGH

0.5V

2.3V

LTC485 • F06

Figure 6. Driver Enable and Disable Times

1.5V

OUTPUT

f = 1MHz, t ≤ 10ns, t ≤ 10ns

PLH

PHL

A, B

–V

OD2

INPUT

LTC485 • F07

Figure 7. Receiver Propagation Delays

1.5V

f = 1MHz, t ≤ 10ns, t ≤ 10ns

1.5V

OUTPUT NORMALLY LOW

OUTPUT NORMALLY HIGH

0.5V

1.5V

LTC485 • F08

Figure 8. Receiver Enable and Disable Times

LTC485

U U

FU CTIO TABLES

PI FU CTIO S

LTC485 Transmitting

PIN #

NAME

DESCRIPTION

INPUTS

OUTPUTS

Receiver Output. If the receiver output is enabled

(RE low), then if A > B by 200mV, RO will be

high. If A < B by 200mV, then RO will be low.

Receiver Output Enable. A low enables the

receiver output, RO. A high input forces the

receiver output into a high impedance state.

Driver Outputs Enable. A high on DE enables the

driver output. A and B, and the chip will function

as a line driver. A low input will force the driver

outputs into a high impedance state and the chip

will function as a line receiver.

Driver Input. If the driver outputs are enabled

(DE high), then a low on DI forces the outputs A

low and B high. A high on DI with the driver

outputs enabled will force A high and B low.

LINE

CONDITION

No Fault

Fault

LTC485 Receiving

INPUTS

OUTPUTS

A – B

≥0.2V

≤–0.2V

Inputs Open

GND

Ground Connection.

Driver Output/Receiver Input.

Positive Supply; 4.75 < V < 5.25

U W

TYPICAL PERFOR A CE CHARACTERISTICS

Receiver Output Low Voltage

vs Output Current

Receiver Output High Voltage

vs Output Current

Receiver Output High Voltage

vs Temperature

–18

–16

–14

–12

–10

–8

4.8

= 25°C

I = 8mA

4.6

4.4

4.2

4.0

3.8

3.6

3.4

3.2

– 6

–4

–2

3.0

0.5

2.0

–50 –25

125

1.0

1.5

75 100

OUTPUT VOLTAGE (V)

TEMPERATURE (°C)

LTC485 • TPC01

LTC485 • TPC02

LTC485 • TPC03

LTC485

TYPICAL PERFOR A CE CHARACTERISTICS

U W

Receiver Output Low Voltage

vs Temperature

Driver Differential Output Voltage

vs Output Current

Driver Differential Output Voltage

vs Temperature

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

2.4

2.3

2.2

2.1

2.0

1.9

1.8

1.7

1.6

= 25°C

RI = 54Ω

I = 8mA

1.5

–50 –25

125

–50 –25

125

75 100

TEMPERATURE (°C)

OUTPUT VOLTAGE (V)

TEMPERATURE (°C)

LTC485 • TPC03

LTC485 • TPC05

LTC485 • TPC06

Driver Output Low Voltage

vs Output Current

Driver Output High Voltage

vs Output Current

TTL Input Threshold

vs Temperature

1.64

1.63

1.62

1.61

1.60

1.59

1.58

1.57

1.56

–108

–96

–84

–72

–60

–48

–36

–24

–12

= 25°C

1.55

–50 –25

125

75 100

TEMPERATURE (°C)

OUTPUT VOLTAGE (V)

LTC485 • TPC09

LTC485 • TPC07

LTC485 • TPC08

Receiver t_PLH– t_PHL

vs Temperature

Driver Skew vs Temperature

Supply Current vs Temperature

7.5

7.0

6.5

6.0

5.5

5.0

4.5

4.0

3.5

5.4

4.8

4.2

3.6

3.0

2.4

1.8

1.2

0.6

640

580

520

460

400

340

280

220

160

DRIVER ENABLED

DRIVER DISABLED

3.0

100

–50 –25

125

–50 –25

125

75 100

–50 –25

125

75 100

TEMPERATURE (°C)

LTC485 • TPC10

LTC485 • TPC11

LTC485 • TPC12

LTC485

U U

APPLICATIO S I FOR ATIO

Basic Theory of Operation

(D1) or the N + /P-substrate diode (D2) respectively will

turn on and clamp the output to the supply. Thus, the

output stage is no longer in a high impedance state and is

not able to meet the RS485 common-mode range require-

ment. In addition, the large amount of current flowing

through either diode will induce the well known CMOS

latchup condition, which could destroy the device.

Previous RS485 transceivers have been designed using

bipolar technology because the common-mode range of

thedevicemustextendbeyondthesuppliesandthedevice

must be immune to ESD damage and latchup. Unfortu-

nately, the bipolar devices draw a large amount of supply

current, which is unacceptable for the numerous applica-

tions that require low power consumption. The LTC485 is

the first CMOS RS485/RS422 transceiver which features

ultra-lowpowerconsumptionwithoutsacrificingESDand

latchup immunity.

The LTC485 output stage of Figure 9 eliminates these

problems by adding two Schottky diodes, SD3 and SD4.

The Schottky diodes are fabricated by a proprietary modi-

fication to the standard N-well CMOS process. When the

output stage is operating normally, the Schottky diodes

are forward biased and have a small voltage drop across

them. When the output is in the high impedance state and

is driven above V_CCor below ground, the parasitic diodes

D1 or D2 still turn on, but SD3 or SD4 will reverse bias and

prevent current from flowing into the N-well or the sub-

strate. Thus, the high impedance state is maintained even

with the output voltage beyond the supplies. With no

minority carrier current flowing into the N-well or sub-

strate, latchup is virtually eliminated under power-up or

power-down conditions.

The LTC485 uses a proprietary driver output stage, which

allows a common-mode range that extends beyond the

power supplies while virtually eliminating latchup and

providing excellent ESD protection. Figure 9 shows the

LTC485 output stage while Figure 10 shows a conven-

tional CMOS output stage.

When the conventional CMOS output stage of Figure 10

enters a high impedance state, both the P-channel (P1)

and the N-channel (N1) are turned off. If the output is then

driven above V_CCor below ground, the P + /N-well diode

SD3

OUTPUT

LOGIC

SD4

LTC485 • F10

LTC485 • F09

Figure 10. Conventional CMOS Output Stage

Figure 9. LTC485 Output Stage

LTC485

APPLICATIO S I FOR ATIO

U U

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 V_CCor 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.

BecausetheESDinjectedcurrentintheN-wellorsubstrate

consists of majority carriers, latchup is prevented by

careful layout techniques.

Propagation Delay

Many digital encoding schemes are dependent upon the

difference in the propagation delay times of the driver and

the receiver. Using the test circuit of Figure 13, Figures 11

and 12 show the typical LTC485 receiver propagation

delay.

The receiver delay times are:

t_PLH– t_PHL= 9ns Typ, V_CC= 5V

The driver skew times are:

Skew = 5ns Typ, V_CC= 5V

10ns Max, V_CC= 5V, T_A= –40°C to 85°C

DRIVER

OUTPUTS

DRIVER

OUTPUTS

RECEIVER

OUTPUT

LTC485 • F11

LTC485 • F12

Figure 11. Receiver t_PHL

Figure 12. Receiver t_PLH

100pF

RECEIVER

OUT

TTL IN

t , t < 6ns

100Ω

LTC485 • F13

100pF

Figure 13. Receiver Propagation Delay Test Circuit

LTC485

U U

APPLICATIO S I FOR ATIO

LTC485 Line Length vs Data Rate

Figures 17 and 18 show that the LTC485 is able to

comfortably drive 4000 feet of wire at 110kHz.

The maximum line length allowable for the RS422/RS485

standard is 4000 feet.

100Ω

TTL

OUT

COMMON-MODE

VOLTAGE (A + B)/2

LTC485

4000 FT 26AWG

TWISTED PAIR

NOISE

TTL

GENERATOR

LTC485 • F17

Figure 14. Line Length Test Circuit

Figure 17. System Common-Mode Voltage at 110kHz

Using the test circuit in Figure 14, Figures 15 and 16 show

that with ~20V_P-Pcommon-mode noise injected on the

line, The LTC485 is able to reconstruct the data stream at

the end of 4000 feet of twisted pair wire.

COMMON-MODE

VOLTAGE (A – B)

COMMON-MODE

LTC485 • F18

VOLTAGE (A + B)/2

Figure 18. System Differential Voltage at 110kHz

When specifying line length vs maximum data rate the

curve in Figure 19 should be used:

LTC485 • F15

Figure 15. System Common-Mode Voltage at 19.2kHz

10k

DIFFERENTIAL

VOLTAGE A – B

100

10k

100k

1M 2.5M

10M

MAXIMUM DATA RATE

LTC485 • F16

LTC485 • F19

Figure 19. Cable Length vs Maximum Data Rate

Figure 16. System Differential Voltage at 19.2kHz

LTC485

TYPICAL APPLICATIO S

Typical RS485 Network

LTC485 • TA03

Dimensions in inches (millimeters) unless otherwise noted.

PACKAGE DESCRIPTIO

J8 Package

8-Lead Ceramic DIP

0.405

(10.287)

0.005

MAX

(0.127)

MIN

0.025

(0.635)

RAD TYP

0.220 – 0.310

(5.588 – 7.874)

0.200

(5.080)

MAX

0.290 – 0.320

(7.366 – 8.128)

CORNER LEADS OPTION

(4 PLCS)

0.015 – 0.060

(0.381 – 1.524)

0.023 – 0.045

(0.584 – 1.143)

HALF LEAD

OPTION

0.008 – 0.018

(0.203 – 0.457)

0° – 15°

0.045 – 0.068

(1.143 – 1.727)

FULL LEAD

OPTION

0.045 – 0.068

(1.143 – 1.727)

0.385 ± 0.025

(9.779 ± 0.635)

0.125

3.175

MIN

0.100 ± 0.010

0.014 – 0.026

(2.540 ± 0.254)

NOTE: LEAD DIMENSIONS APPLY TO SOLDER DIP OR TIN PLATE LEADS.

(0.360 – 0.660)

J8 0293

LTC485

Dimensions in inches (millimeters) unless otherwise noted.

PACKAGE DESCRIPTIO

N8 Package

8-Lead Plastic DIP

0.400

(10.160)

MAX

0.250 ± 0.010

(6.350 ± 0.254)

0.130 ± 0.005

0.300 – 0.320

0.045 – 0.065

(3.302 ± 0.127)

(1.143 – 1.651)

(7.620 – 8.128)

0.065

(1.651)

TYP

0.009 – 0.015

(0.229 – 0.381)

0.125

0.020

(0.508)

MIN

(3.175)

MIN

+0.025

0.045 ± 0.015

(1.143 ± 0.381)

0.325

–0.015

+0.635

8.255

(

)

–0.381

0.100 ± 0.010

(2.540 ± 0.254)

0.018 ± 0.003

(0.457 ± 0.076)

N8 0392

S8 Package

8-Lead Plastic SOIC

0.189 – 0.197

(4.801 – 5.004)

0.228 – 0.244

0.150 – 0.157

(5.791 – 6.197)

(3.810 – 3.988)

0.010 – 0.020

(0.254 – 0.508)

× 45°

0.053 – 0.069

(1.346 – 1.752)

0.004 – 0.010

(0.101 – 0.254)

0.008 – 0.010

(0.203 – 0.254)

0°– 8° TYP

0.016 – 0.050

0.406 – 1.270

0.050

(1.270)

BSC

0.014 – 0.019

(0.355 – 0.483)

SO8 0392

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 represen-

tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.

LTC485

U.S. Area Sales Offices

SOUTHEAST REGION

Linear Technology Corporation

17060 Dallas Parkway

Suite 208

Dallas, TX 75248

Phone: (214) 733-3071

FAX: (214) 380-5138

SOUTHWEST REGION

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22141 Ventura Blvd.

NORTHEAST REGION

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2300 E. Lincoln Hwy.,Suite 306

Langhorne, PA 19047

Phone: (215) 757-8578

FAX: (215) 757-5631

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Woodland Hills, CA 91364

Phone: (818) 703-0835

FAX: (818) 703-0517

CENTRAL REGION

Linear Technology Corporation

Chesapeake Square

NORTHWEST REGION

Linear Technology Corporation

782 Sycamore Dr.

Linear Technology Corporation

266 Lowell St., Suite B-8

Wilmington, MA 01887

Phone: (508) 658-3881

FAX: (508) 658-2701

229 Mitchell Court, Suite A-25

Addison, IL 60101

Phone: (708) 620-6910

FAX: (708) 620-6977

Milpitas, CA 95035

Phone: (408) 428-2050

FAX: (408) 432-6331

International Sales Offices

FRANCE

KOREA

TAIWAN

Linear Technology S.A.R.L.

Immeuble "Le Quartz"

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92290 Chatenay Malabry

France

Linear Technology Korea Branch

Namsong Building, #505

Itaewon-Dong 260-199

Yongsan-Ku, Seoul

Korea

Linear Technology Corporation

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Chung Shan N. Rd.

Taipei, Taiwan, R.O.C.

Phone: 886-2-521-7575

FAX: 886-2-562-2285

Phone: 33-1-41079555

FAX: 33-1-46314613

Phone: 82-2-792-1617

FAX: 82-2-792-1619

UNITED KINGDOM

GERMANY

SINGAPORE

Linear Technology (UK) Ltd.

The Coliseum, Riverside Way

Camberley, Surrey GU15 3YL

United Kingdom

Phone: 44-276-677676

FAX: 44-276-64851

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Untere Hauptstr. 9

D-85386 Eching

Germany

Phone: 49-89-3197410

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101 Boon Keng Road

#02-15 Kallang Ind. Estates

Singapore 1233

Phone: 65-293-5322

FAX: 65-292-0398

JAPAN

Linear Technology KK

5F YZ Bldg.

Iidabashi, Chiyoda-Ku

Tokyo, 102 Japan

Phone: 81-3-3237-7891

FAX: 81-3-3237-8010

World Headquarters

Linear Technology Corporation

1630 McCarthy Blvd.

Milpitas, CA 95035-7487

Phone: (408) 432-1900

FAX: (408) 434-0507

06/24/93

LT/GP 0294 5K REV E • PRINTED IN THE USA

LINEAR TECHNOLOGY CORPORATION 1994

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7487

●

(408) 432-1900 FAX: (408) 434-0507 TELEX: 499-3977

LTC485C [Linear]

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