LTC489_15_技术文档

LTC488/LTC489

Quad RS485 Line Receiver

FEATURES

DESCRIPTION

The LTC^®488 and LTC489 are low power differential bus/

line receivers designed for multipoint data transmission

standard RS485 applications with extended common

mode range (12V to –7V). They also meet the require-

ments of RS422.

n

Low Power: I = 7mA Typ

CC

n

Designed for RS485 or RS422 Applications

n

Single 5V Supply

n

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

Ground Difference Between Devices on the Bus

n

60mV Typical Input Hysteresis

The CMOS design offers signiﬁcant power savings over

its bipolar counterpart without sacriﬁcing ruggedness

against overload or ESD damage.

n

Receiver Maintains High Impedance in Three-State or

with the Power Off

28ns Typical Receiver Propagation Delay

n

Thereceiverfeaturesthree-stateoutputs,withthereceiver

output maintaining high impedance over the entire com-

mon mode range.

Pin Compatible with the SN75173 (LTC488)

Pin Compatible with the SN75175 (LTC489)

The receiver has a fail-safe feature which guarantees a

high output state when the inputs are left open.

APPLICATIONS

n

Low Power RS485/RS422 Receivers

Both AC and DC speciﬁcations are guaranteed 4.75V to

5.25V supply voltage range.

L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other

trademarks are the property of their respective owners.

n

Level Translator

TYPICAL APPLICATION

EN

4

2

1

12

DRIVER

1/4 LTC486

RECEIVER

1/4 LTC488

3

120Ω

RO

DI

4000 FT 24 GAUGE TWISTED PAIR

EN12

4

2

1

DRIVER

1/4 LTC487

RECEIVER

1/4 LTC489

3

120Ω

RO

DI

4000 FT 24 GAUGE TWISTED PAIR

4889 TA01

4889fb

1

LTC488/LTC489

ABSOLUTE MAXIMUM RATINGS

(Note 1)

Supply Voltage (V ) ................................................12V

Operating Temperature Range

CC

Control Input Currents .......................... –25mA to 25mA

LTC488C/LTC489C ................................... 0°C to 70°C

LTC488I/LTC489I..................................–40°C to 85°C

Storage Temperature Range...................–65°C to 150°C

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

Control Input Voltages ..................–0.5V to (V + 0.5V)

CC

Receiver Input Voltages .......................................... 14V

Receiver Output Voltages..............–0.5V to (V + 0.5V)

CC

PIN CONFIGURATION

LTC488

TOP VIEW

B1

A1

1

2

3

4

5

6

7

8

16

V

B1

A1

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

V

CC

R

15 B4

B4

R

RO1

EN

14

13

12

11

10

9

A4

RO1

EN

A4

RO4

EN

RO4

EN

RO2

A2

RO2

A2

RO3

A3

RO3

A3

R

B2

R

GND

B3

GND

B3

SW PACKAGE

16-LEAD PLASTIC (WIDE) SO

N PACKAGE

16-LEAD PLASTIC DIP

T

= 150°C, θ = 90°C/W

T

= 150°C, θ = 70°C/W

JMAX

JA

JMAX

JA

LTC489

TOP VIEW

B1

A1

1

16

V

B1

A1

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

V

CC

R

2

3

4

5

6

7

8

15 B4

B4

R

RO1

EN12

RO2

A2

14

13

12

11

10

9

A4

RO1

EN12

RO2

A2

A4

RO4

EN34

RO3

A3

RO4

EN34

RO3

A3

R

B2

R

GND

B3

GND

B3

SW PACKAGE

16-LEAD PLASTIC (WIDE) SO

= 150°C, θ = 90°C/W

N PACKAGE

16-LEAD PLASTIC DIP

T

= 150°C, θ = 70°C/W

JMAX

JA

JMAX

JA

4889fb

2

LTC488/LTC489

ORDER INFORMATION

LEAD FREE FINISH

LTC488CN#PBF

LTC488CSW#PBF

LTC488IN#PBF

TAPE AND REEL

PART MARKING

LTC488CN

PACKAGE DESCRIPTION

16-Lead Plastic DIP

16-Lead Plastic SO

16-Lead Plastic DIP

16-Lead Plastic SO

16-Lead Plastic DIP

16-Lead Plastic SO

16-Lead Plastic DIP

16-Lead Plastic SO

TEMPERATURE RANGE

0°C to 70°C

LTC488CN#TRPBF

LTC488CSW#TRPBF

LTC488IN#TRPBF

LTC488ISW#TRPBF

LTC489CN#TRPBF

LTC489CSW#TRPBF

LTC489IN#TRPBF

LTC489ISW#TRPBF

LTC488CSW

LTC488IN

0°C to 70°C

–40°C to 85°C

0°C to 70°C

LTC488ISW#PBF

LTC489CN#PBF

LTC489CSW#PBF

LTC489IN#PBF

LTC488ISW

LTC489CN

LTC489CSW

LTC489IN

0°C to 70°C

–40°C to 85°C

LTC489ISW#PBF

LTC489ISW

Consult LTC Marketing for parts speciﬁed with wider operating temperature ranges.

Consult LTC Marketing for information on non-standard lead based ﬁnish parts.

For more information on lead free part marking, go to: http://www.linear.com/leadfree/

For more information on tape and reel speciﬁcations, go to: http://www.linear.com/tapeandreel/

DC ELECTRICAL CHARACTERISTICS ^Thel denotes the speciﬁcations which apply over the full operating

temperature range, otherwise speciﬁcations are at T_A= 25°C. V_CC= 5V (Notes 2, 3), unless otherwise noted.

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

l

V

Input High Voltage

Input Low Voltage

Input Current

EN, EN, EN12, EN34

2.0

V

INH

INL

0.8

2

I

IN1

I

IN2

μA

l

Input Current (A, B)

V

= 0V or 5.25V, V = 12V

= 0V or 5.25V, V = – 7V

1.0

–0.8

mA

CC

IN

l

V

Differential Input Threshold Voltage for Receiver

Receiver Input Hysteresis

–7V ≤ V ≤ 12V

–0.2

3.5

0.2

V

mV

V

TH

CM

ΔV

V

CM

= 0V

60

7

TH

l

V

OH

V

OL

Receiver Output High Voltage

Receiver Output Low Voltage

Three-State Output Current at Receiver

Supply Current

I = –4mA, V = 0.2V

O ID

I = 4mA, V = –0.2V

0.4

1

V

O

ID

I

V

CC

= Max 0.4V ≤ V ≤ 2.4V

μA

mA

kΩ

mA

ns

OZR

CC

O

No Load, Digital Pins = GND or V

10

CC

R

Receiver Input Resistance

–7V ≤ V ≤ 12V, V = 0V

12

7

IN

CM

CC

I

t

Receiver Short-Circuit Current

Receiver Input to Output

0V ≤ V ≤ V

CC

85

55

OSR

PLH

PHL

SKD

O

C = 15pF (Figures 1, 3)

L

12

28

4

Receiver Input to Output

C = 15pF (Figures 1, 3)

L

ns

| t

– t

|

C = 15pF (Figures 1, 3)

L

ns

PLH

PHL

Differential Receiver Skew

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

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

SYMBOL

PARAMETER

CONDITIONS

C = 15pF (Figures 2, 4) S1 Closed

MIN

TYP

30

MAX

60

UNITS

ns

l

t

ZL

t

ZH

t

LZ

t

HZ

Receiver Enable to Output Low

Receiver Enable to Output High

Receiver Disable from Low

Receiver Disable from High

L

C = 15pF (Figures 2, 4) S2 Closed

L

30

60

ns

C = 15pF (Figures 2, 4) S1 Closed

L

30

60

ns

C = 15pF (Figures 2, 4) S2 Closed

L

30

60

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.

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

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

otherwise speciﬁed.

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

CC

A

4889fb

3

LTC488/LTC489

TYPICAL PERFORMANCE CHARACTERISTICS

Receiver Output Low Voltage vs

Temperature at I = 8mA

Receiver Output High Voltage vs

Temperature at I = 8mA

Receiver Output High Voltage vs

Output Current at T_A= 25°C

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

4.8

4.6

4.4

–18

–16

–14

–12

–10

4.2

4.0

3.8

3.6

3.4

3.2

3.0

–8

–6

–4

–2

0

–50 –25

0

25

50

75 100 125

–50 –25

0

25

50

75 100 125

5

4

3

2

TEMPERATURE (°C)

OUTPUT VOLTAGE (V)

4889 G01

4889 G02

4889 G03

Receiver Output Low Voltage vs

Output Current at T_A= 25°C

TTL Input Threshold vs

Temperature

36

32

28

24

20

1.63

1.61

1.59

1.57

16

12

8

4

1.55

0

–50 –25

0

25

50

75 100 125

0

0.5

1.5

OUTPUT VOLTAGE (V)

1.0

2.0

TEMPERATURE (°C)

8889 G05

4889 G04

Receiver |t_PLH– t_PHL| vs

Temperature

Supply Current vs Temperature

7.0

6.6

6.2

5.8

5

4

3

2

5.4

1

–50 –25

0

25

50

75 100 125

–50 –25

0

25

50

75 100 125

TEMPERATURE (°C)

4889 G07

4889 G06

4889fb

4

LTC488/LTC489

PIN FUNCTIONS

B 1 (Pin 1): Receiver 1 Input.

GND (Pin 8): Ground Connection.

A1 (Pin 2): Receiver 1 Input.

B3 (Pin 9): Receiver 3 Input.

RO1 (Pin 3): Receiver 1 Output. If the receiver output

is enabled, then if A > B by 200mV, RO1 will be high. If

A < B by 200mV, then RO1 will be low.

A3 (Pin 10): Receiver 3 Input.

RO3 (Pin 11): Receiver 3 Output. Refer to RO1.

EN (Pin 12) LTC488: Receiver Output Disabled. See Func-

tion Table for details.

EN(Pin4)LTC488:ReceiverOutputEnabled.SeeFunction

Table for details.

EN34 (Pin 12) LTC489: Receiver 3, Receiver 4 output

enabled. See Function Table for details.

EN12 (Pin 4) LTC489: Receiver 1, Receiver 2 Output

Enabled. See Function Table for details.

RO4 (Pin 13): Receiver 4 Output. Refer to RO1.

A4 (Pin 14): Receiver 4 Input.

RO2 (Pin 5): Receiver 2 Output. Refer to RO1.

A2 (Pin 6): Receiver 2 Input.

B4 (Pin 15): Receiver 4 Input.

B2 (Pin 7): Receiver 2 Input.

V

(Pin 16): Positive Supply; 4.75V ≤ V ≤ 5.25V.

CC

FUNCTION TABLES

LTC488

LTC489

DIFFERENTIAL

ENABLES

OUTPUT

DIFFERENTIAL

A – B

ENABLES

OUTPUT

A – B

EN

RO

EN12 or EN34

RO

H

?

V

≥ 0.2V

H

X

L

H

V

≥ 0.2V

ID

H

L

ID

–0.2V < V < 0.2V

ID

–0.2V < V < 0.2V

H

X

L

?

ID

V

X

≤ 0.2V

L

ID

Z

V

X

≤ 0.2V

H

X

L

ID

H: High Level

L: Low Level

X: Irrelevant

?: Indeterminate

Z: High Impedance (Off)

L

H

Z

4889fb

5

LTC488/LTC489

TEST CIRCUITS

100pF

A

B

D

RO

DRIVER

RECEIVER

54Ω

C

L

100pF

4889 F01

Figure 1. Receiver Timing Test Circuit

Note: The input pulse is supplied by a generator having the following characteristics:

f = 1MHz, Duty Cycle = 50%, t < 10ns, t ≤ 10ns, Z

= 50Ω

r

f

OUT

S1

S2

1k

RECEIVER

OUTPUT

V

CC

C

1k

L

4889 F02

Figure 2. Receiver Enable and Disable Timing Test Circuit

SWITCHING TIME WAVEFORMS

INPUT

f = 1MHz; t ≤ 10ns; t ≤ 10ns

V

OD2

r

f

INPUT

A, B

0V

t

0V

–V

OD2

t

PHL

PLH

V

OH

RO

1.5V

V

OL

4889 F03

Figure 3. Receiver Propagation Delays

3V

f = 1MHz; t ≤ 10ns; t ≤ 10ns

r

f

EN OR

EN12

1.5V

0V

5V

t

ZL

t

LZ

RO

1.5V

OUTPUT NORMALLY LOW

OUTPUT NORMALLY HIGH

0.5V

V

OL

t

ZH

HZ

V

OH

0.5V

1.5V

0V

4889 F04

Figure 4. Receiver Enable and Disable Times

4889fb

6

LTC488/LTC489

APPLICATIONS INFORMATION

Typical Application

Cables and Data Rate

A typical connection of the LTC488/LTC489 is shown in

Figure 5. Two twisted-pair wires connect up to 32 driver/

receiver pairs for half-duplex data transmission. There are

no restrictions on where the chips are connected to the

wires, and it isn’t necessary to have the chips connected

at the ends. However, the wires must be terminated only

at the ends with a resistor equal to their characteristic

impedance, typically 120Ω. The input impedance of a

receiver is typically 20k to GND, or 0.5 unit RS485 load,

so in practice 50 to 60 transceivers can be connected to

the same wires. The optional shields around the twisted-

pair help reduce unwanted noise, and are connected to

GND at one end.

ThetransmissionlineofchoiceforRS485applicationsisa

twisted-pair. There are coaxial cables (twinaxial) made for

this purpose that contain straight-pairs, but these are less

ﬂexible, more bulky, and more costly than twisted-pairs.

Many cable manufacturers offer a broad range of 120Ω

cables designed for RS485 applications.

Losses in a transmission line are a complex combination

of DC conductor loss, AC losses (skin effect), leakage, and

AClossesinthedielectric.Ingoodpolyethylenecablesuch

as the Belden 9841, the conductor losses and dielectric

losses are of the same order of magnitude, leading to

relatively low overall loss (Figure 6).

When using low loss cables, Figure 7 can be used as a

guidelineforchoosingthemaximumlinelengthforagiven

EN

SHIELD

4

2

3

RX

DX

1/4 LTC486

1

3

1/4 LTC488 OR

1/4 LTC489

DX

120Ω

RX

1

12

1

2

EN

1/4 LTC488 OR

1/4 LTC489

RX

3

2

12

DX

1/4 LTC486

4

4889 F05

EN

3

1

DX

RX

Figure 5. Typical Connection

10

10k

1k

1

100

10

0.1

2.5M

10k

100k

1M

10M

0.1

1

10

100

DATA RATE (bps)

FREQUENCY (MHz)

4889 F07

4889 F06

Figure 6. Attenuation vs Frequency for Belden 9841

Figure 7. Cable Length vs Data Rate

4889fb

7

LTC488/LTC489

APPLICATIONS INFORMATION

datarate. WithlowerqualityPVCcables, thedielectricloss

factor can be 1000 times worse. PVC twisted-pairs have

terrible losses at high data rates (> 100kbps), and greatly

reduce the maximum cable length. At low data rates how-

ever, they are acceptable and much more economical.

When the reﬂected signal returns to the driver, the ampli-

tude will be lowered. The width of the pedestal is equal to

twice the electrical length of the cable (about 1.5ns/foot).

If the cable is lightly loaded (470Ω), the signal reﬂects

in phase and increases the amplitude at the drive output.

An input frequency of 30kHz is adequate for tests out to

4000 ft. of cable.

Cable Termination

The proper termination of the cable is very important. If

the cable is not terminated with its characteristic imped-

ance, distorted waveforms will result. In severe cases,

distorted (false) data and nulls will occur. A quick look

at the output of the driver will tell how well the cable is

terminated. It is best to look at a driver connected to the

end of the cable, since this eliminates the possibility of

getting reﬂections from two directions. Simply look at the

driver output while transmitting square wave data. If the

cable is terminated properly, the waveform will look like

a square wave (Figure 8).

AC Cable Termination

Cable termination resistors are necessary to prevent un-

wanted 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 60 times greater

than the supply current of the LTC488/LTC489. One way

to eliminate the unwanted current is by AC coupling the

termination resistors as shown in Figure 9.

If the cable is loaded excessively (47Ω), the signal initially

sees the surge impedance of the cable and jumps to an

initial amplitude. The signal travels down the cable and is

reﬂectedbackoutofphasebecauseofthemistermination.

The coupling capacitor must allow high frequency energy

to ﬂow to the termination, but block DC and low frequen-

cies. The dividing line between high and low frequency

depends on the length of the cable. The coupling capaci-

tor must pass frequencies above the point where the line

represents an electrical one-tenth wavelength. The value

of the coupling capacitor should therefore be set at 16.3pF

perfootofcablelengthfor120Ωcables. Withthecoupling

capacitors in place, power is consumed only on the signal

edges, and not when the driver output is idling at a 1 or 0

state. A 100nF capacitor is adequate for lines up to 4000

feet in length. Be aware that the power savings start to

decrease once the data rate surpasses 1/(120Ω)(C).

PROBE HERE

Rt

DRIVER

RECEIVER

DX

RX

Rt = 120Ω

Rt = 47Ω

120Ω

RECEIVER

RX

C

Rt = 470Ω

488/9 F09

C = LINE LENGTH (FT)(16.3pF)

4889 F08

Figure 9. AC-Coupled Termination

Figure 8. Termination Effects

4889fb

8

LTC488/LTC489

APPLICATIONS INFORMATION

Receiver Open-Circuit Fail-Safe

The termination resistors are used to generate a DC bias

which forces the receiver output to a known state, in this

case a logic 0. The ﬁrst method consumes about 208mW

andthesecondabout8mW.Thelowestpowersolutionisto

use an AC termination with a pullup resistor. Simply swap

the receiver inputs for data protocols ending in logic 1.

Somedataencodingschemesrequirethattheoutputofthe

receiver maintains a known state (usually a logic 1) when

the data is ﬁnished transmitting and all drivers on the line

areforcedinthree-state.ThereceiveroftheLTC488/LTC489

has a fail-safe feature which guarantees the output to be

in a logic 1 state when the receiver inputs are left ﬂoating

(open-circuit). When the input is terminated with 120Ω

and the receiver output must be forced to a known state,

the circuits of Figure 10 can be used.

Fault Protection

AllofLTC’sRS485productsareprotectedagainstESDtran-

sientsupto2kVusingthehumanbodymodel(100pF,1.5k).

However,someapplicationsneedmoreprotection.Thebest

protectionmethodistoconnectabidirectionalTransZorb^®

from each line side pin to ground (Figure 11).

5V

110Ω 130Ω

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 instruments, GSI, and come in a variety of break-

down 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.

RECEIVER

RX

130Ω 110Ω

5V

1.5k

120Ω

1.5k

RECEIVER

RX

Y

5V

DRIVER

120Ω

100k

Z

C

RECEIVER

RX

4889 F11

120Ω

Figure 11. ESD Protection with TransZorbs

4889 F10

Figure 10. Forcing “0” When All Drivers Are Off

4889fb

9

LTC488/LTC489

PACKAGE DESCRIPTION

N Package

16-Lead PDIP (Narrow .300 Inch)

(Reference LTC DWG # 05-08-1510)

.770*

(19.558)

MAX

14

12

10

9

8

15

13

11

16

.255 .015*

(6.477 0.381)

2

1

3

4

6

5

7

.300 – .325

(7.620 – 8.255)

.130 .005

(3.302 0.127)

.045 – .065

(1.143 – 1.651)

.020

(0.508)

MIN

.065

(1.651)

TYP

.008 – .015

(0.203 – 0.381)

+.035

–.015

.325

.120

(3.048)

MIN

.018 .003

(0.457 0.076)

.100

(2.54)

BSC

+0.889

8.255

(

)

–0.381

NOTE:

INCHES

MILLIMETERS

1. DIMENSIONS ARE

N16 1002

*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.

MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm)

4889fb

10

LTC488/LTC489

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

15 14

12

10

9

N

16

N

13

11

.325 .005

.420

MIN

.394 – .419

(10.007 – 10.643)

NOTE 3

N/2

8

1

2

3

N/2

RECOMMENDED SOLDER PAD LAYOUT

2

3

5

7

1

4

6

.291 – .299

(7.391 – 7.595)

NOTE 4

.037 – .045

(0.940 – 1.143)

.093 – .104

(2.362 – 2.642)

.010 – .029

× 45°

(0.254 – 0.737)

.005

(0.127)

RAD MIN

0° – 8° TYP

.050

(1.270)

BSC

.004 – .012

.009 – .013

(0.102 – 0.305)

NOTE 3

(0.229 – 0.330)

.014 – .019

.016 – .050

(0.356 – 0.482)

TYP

(0.406 – 1.270)

NOTE:

1. DIMENSIONS IN

INCHES

(MILLIMETERS)

S16 (WIDE) 0502

2. DRAWING NOT TO SCALE

3. PIN 1 IDENT, NOTCH ON TOP AND CAVITIES ON THE BOTTOM OF PACKAGES ARE THE MANUFACTURING OPTIONS.

THE PART MAY BE SUPPLIED WITH OR WITHOUT ANY OF THE OPTIONS

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

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

4889fb

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 representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

11

LTC488/LTC489

TYPICAL APPLICATION

RS232 Receiver

RS232

IN

RECEIVER

1/4 LTC488 OR

1/4 LTC489

RX

5.6k

4889 TA02

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10Mbps Operation

Ultralow Power RS485 with Low EMI and High Input Impedance

High Speed RS485 Transceiver

Up to 256 Nodes on a Bus

52Mbps, Pin Compatible with LTC485

52Mbps, Pin Compatible LTC490/LTC491

LTC1686/LTC1687 High Speed RS485 Full-Duplex Transceiver

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LT 0309 REV B • PRINTED IN USA

LinearTechnology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

12

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(408) 432-1900 FAX: (408) 434-0507 www.linear.com


型号：	LTC489_15
厂家：	Linear
描述：	Quad RS485 Line Receiver
文件：	总12页 (文件大小：137K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

LTC489_15 [Linear]

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