LT1483_技术文档

LTC1483

Ultra-Low Power RS485 Low EMI

Transceiver with Shutdown

U

DESCRIPTIO

EATURE

S

F

The LTC^®1483 is an ultra-low power differential line trans-

ceiver designed for data transmission standard RS485

applications with extended common-mode range (–7V to

12V). It will also meet the requirements of RS422. The

LTC1483featuresoutputdriverswithcontrolledslewrate,

decreasing the EMI radiated from the RS485 lines, and

improving signal fidelity with misterminated lines. The

CMOS design offers significant power savings over its

bipolarcounterpartswithoutsacrificingruggednessagainst

overloadorESDdamage. Typicalquiescentcurrentisonly

80µA while operating and less than 1µA in shutdown.

■

Low Power: I_CC= 120µA Max with Driver Disabled

I_CC= 500µA Max with Driver Enabled, No Load

1µA Quiescent Current in Shutdown Mode

Controlled Slew Rate Driver for Reduced EMI

Single 5V Supply

Drivers/Receivers Have ±10kV ESD Protection

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

Ground Difference Between Devices on the Data Line

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

■

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

inputsareleftopen. I/Opinsareprotectedagainstmultiple

ESD strikes of over ±10kV.

■

Up to 32 Transceivers on the Bus

Pin Compatible with the LTC485

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PPLICATI

S

A

■

Battery-Powered RS485/RS422 Applications

Low Power RS485/RS422 Transceiver

Level Translator

The LTC1483 is fully specified over the commercial and

extended industrial temperature range and is available in

8-pin DIP and SO packages.

, LTC and LT are registered trademarks of Linear Technology Corporation.

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O

TYPICAL APPLICATI

RO1

RE1

DE1

DI1

V

CC1

R

DI

R

TERM

D

GND1

A – B

RO2

RE2

DE2

DI2

V

CC2

R

RO

D

GND2

LTC1483 • TA01

1483 TA02

1

LTC1483

W W W

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W

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ABSOLUTE AXI U RATI GS

/O

PACKAGE RDER I FOR ATIO

(Note 1)

ORDER PART

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

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

Operating Temperature Range

LTC1483C........................................ 0°C ≤ T_A≤ 70°C

LTC1483I.................................... –40°C ≤ T_A≤ 85°C

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

TOP VIEW

NUMBER

RO

RE

DE

DI

1

2

3

4

V

B

A

8

7

6

5

CC

R

LTC1483CN8

LTC1483IN8

LTC1483CS8

LTC1483IS8

D

GND

N8 PACKAGE

8-LEAD PDIP

S8 PACKAGE

8-LEAD PLASTIC SO

S8 PART MARKING

T_JMAX= 125°C, θ_JA= 130°C/ W (N8)

T_JMAX= 125°C, θ_JA= 150°C/ W (S8)

1483

1483I

Consult factory for Military grade parts.

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

ELECTRICAL CHARACTERISTICS

SYMBOL PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

V

OD1

V

OD2

Differential Driver Output Voltage (Unloaded)

Differential Driver Output Voltage (with Load)

I = 0

●

5

V

O

R = 50Ω (RS422)

R = 27Ω (RS485), Figure 1

●

2

1.5

V

5

∆V

OD

Change in Magnitude of Driver Differential Output

Voltage for Complementary Output States

R = 27Ω or R = 50Ω, Figure 1

●

0.2

V

Driver Common-Mode Output Voltage

R = 27Ω or R = 50Ω, Figure 1

●

3

V

OC

∆ V

Change in Magnitude of Driver Common-Mode

Output Voltage for Complementary Output States

0.2

OC

V

Input High Voltage

Input Low Voltage

Input Current

DE, DI, RE

●

2

V

IH

0.8

IL

I

±2

µA

IN1

IN2

Input Current (A, B)

DE = 0, V = 0V or 5.25V, V = 12V

●

1.0

–0.8

mA

CC

IN

DE = 0, V = 0V or 5.25V, V = –7V

CC

IN

V

Differential Input Threshold Voltage for Receiver

Receiver Input Hysteresis

–7V ≤ V ≤ 12V

●

–0.2

3.5

0.2

V

mV

V

TH

CM

∆V

V

= 0V

CM

45

25

TH

V

Receiver Output High Voltage

I = –4mA, V = 200mV

O ID

OH

Receiver Output Low Voltage

I = 4mA, V = –200mV

0.4

V

OL

O

ID

I

Three-State (High Impedance) Output

Current at Receiver

V

= Max, 0.4V ≤ V ≤ 2.4V

±1

µA

OZR

CC

O

R

Receiver Input Resistance

Supply Current

–7V ≤ V ≤ 12V

●

12

kΩ

IN

CM

I

CC

No Load, Output Enabled

No Load, Output Disabled

●

300

80

500

120

µA

I

Supply Current in Shutdown Mode

DE = 0, RE = V

1

10

250

85

µA

mA

SHDN

OSD1

OSD2

OSR

CC

Driver Short-Circuit Current, V

Receiver Short-Circuit Current

= HIGH

= LOW

–7V ≤ V ≤ 12V

●

35

7

OUT

O

–7V ≤ V ≤ 12V

O

0V ≤ V ≤ V

O

CC

2

LTC1483

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

LTC1483

TYP

SYMBOL PARAMETER

CONDITIONS

= 54Ω, C = C = 100pF,

(Figures 3, 5)

MIN

150

MAX

1200

600

UNITS

ns

t

Driver Input to Output

R

●

PLH

DIFF

L1

L2

Driver Input to Output

ns

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

100

ns

SKEW

t , t

150

100

150

30

1200

1500

200

ns

r

f

t

f

t

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

L

ns

ZH

ZL

LZ

HZ

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

L

ns

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

L

ns

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

L

ns

R

= 54Ω, C = C = 100pF,

140

13

ns

PLH

DIFF

L1

L2

(Figures 3, 7)

30

200

ns

PHL

t

– t Differential Receiver Skew

PHL

ns

SKD

PLH

Receiver Enable to Output Low

C

= 15pF (Figures 2, 8), S1 Closed

= 15pF (Figures 2, 8), S2 Closed

= 15pF (Figures 2, 8), S1 Closed

= 15pF (Figures 2, 8), S2 Closed

20

50

ns

ZL

RL

Receiver Enable to Output High

Receiver Disable from Low

20

ns

ZH

20

ns

LZ

Receiver Disable from High

20

ns

HZ

Maximum Data Rate

250

50

kbits/s

ns

MAX

Time to Shutdown

DE = 0, RE =

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

200

600

SHDN

ZH(SHDN)

ZL(SHDN)

ZH(SHDN)

ZL(SHDN)

Driver Enable from Shutdown to Output High

Driver Enable from Shutdown to Output Low

Receiver Enable from Shutdown to Output High

Receiver Enable from Shutdown to Output Low

2000

3500

ns

L

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

L

ns

C = 15pF (Figures 2, 8), S2 Closed

L

ns

C = 15pF (Figures 2, 8), S1 Closed

L

ns

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.

The

●

denotes specifications which apply over the full operating

temperature range.

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

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

the device cannot be guaranteed.

CC

A

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TYPICAL PERFORMANCE CHARACTERISTICS

Receiver t_PLH– t_PHLvs

Temperature

Driver Differential Output Voltage

vs Output Current

Supply Current vs Temperature

14

12

10

8

70

60

50

40

30

20

10

0

350

300

250

200

150

100

50

T

= 25°C

A

THERMAL SHUTDOWN

WITH DRIVER ENABLED

DRIVER ENABLED

6

4

DRIVER DISABLED

2

0

–50 –25

0

25

50

TEMPERATURE (°C)

75

100 125

0

1

2

3

4

5

–50 –25

0

25

75 100 125 150 175

50

OUTPUT VOLTAGE (V)

TEMPERATURE (°C)

1483 G01

1483 G02

1483 G03

3

LTC1483

TYPICAL PERFORMANCE CHARACTERISTICS

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Driver Differential Output Voltage

vs Temperature

Driver Output Low Voltage

vs Output Current

Driver Output High Voltage

vs Output Current

70

60

50

40

30

20

10

0

2.5

2.4

2.3

2.2

2.1

2.0

1.9

1.8

1.7

1.6

1.5

0

–10

–20

–30

–40

–50

–60

–70

–80

–90

T

A

= 25°C

R

= 54Ω

L

T

= 25°C

A

1

2

3

4

0

–50

0

25

50

75 100 125

–25

0

4

5

1

2

3

OUTPUT VOLTAGE

TEMPERATURE (°C)

OUTPUT VOLTAGE (V)

1483 G05

1483 G04

1483 G06

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PIN FUNCTIONS

RO (Pin 1): 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.

DI (Pin 4): Driver Input. If the driver outputs are enabled

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

high.AhighonDIwiththedriveroutputsenabledwillforce

A high and B low.

RE (Pin 2): Receiver Output Enable. A low enables the

receiver output, RO. A high input forces the receiver

output into a high impedance state.

GND (Pin 5): Ground.

A (Pin 6): Driver Output/Receiver Input.

B (Pin 7): Driver Output/Receiver Input.

V_CC(Pin 8): Positive Supply. 4.75V < V_CC< 5.25V.

DE (Pin 3): Driver Outputs Enable. A high on DE enables

the driver output. A, 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.IfREishighandDEislow,thepartwillenteralow

power (1µA) shutdown state.

U

FU CTIO TABLES

LTC1483 Transmitting

INPUTS

LTC1483 Receiving

OUTPUTS

INPUTS

OUTPUTS

RE

X

DE

1

DI

1

B

0

A

RE

0

DE

0

A – B

≥0.2V

RO

1

X

1

0

1

0

≤–0.2V

Inputs Open

X

0

X

Z

0

1

0

Z*

1

0

Z*

*Shutdown mode for LTC1483

4

LTC1483

TEST CIRCUITS

A

S1

S2

TEST POINT

1k

RECEIVER

OUTPUT

R

V

CC

V

OD

1k

V

C

RL

OC

B

LTC1483 • F02

LTC1483 • F01

Figure 1. Driver DC Test Load

Figure 2. Receiver Timing Test Load

3V

DE

S1

A

B

C

V

CC

L1

DI

500Ω

OUTPUT

UNDER TEST

RO

R

DIFF

B

S2

C

L2

C

L

RE

15pF

LTC1483 • F04

LTC1483 • F03

Figure 3. Driver/Receiver Timing Test Circuit

Figure 4. Driver Timing Test Load

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SWITCHI G TI E WAVEFOR S

3V

t ≤ 10ns, t ≤ 10ns

DI

1.5V

r

f

0V

B

1/2 V

O

t

PHL

PLH

V

O

A

t

SKEW

1/2 V

SKEW

O

V

O

90%

10%

90%

V

DIFF

= V(A) – V(B)

0V

10%

–V

O

LTC1483 • F05

t

f

r

Figure 5. Driver Propagation Delays

3V

0V

5V

t ≤ 10ns, t ≤ 10ns

1.5V

DE

A, B

r

f

t

, t

LZ

ZL(SHDN) ZL

2.3V

OUTPUT NORMALLY LOW

0.5V

V

OL

OH

0V

V

OUTPUT NORMALLY HIGH

, t

2.3V

t

LTC1483 • F06

HZ

ZH(SHDN) ZH

Figure 6. Driver Enable and Disable Times

5

LTC1483

U

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SWITCHI G TI E WAVEFOR S

V

OH

1.5V

RO

OUTPUT

V

OL

t

t ≤ 10ns, t ≤ 10ns

t

PHL

r

f

PLH

V

A – B

–V

OD2

0V

INPUT

LTC1483 • F07

Figure 7. Receiver Propagation Delays

3V

0V

5V

1.5V

RE

RO

t ≤ 10ns, t ≤ 10ns

r

f

t

, t

t

ZL(SHDN) ZL

LZ

1.5V

OUTPUT NORMALLY LOW

0.5V

OUTPUT NORMALLY HIGH

, t

1.5V

t

0V

t

LTC1483 • F08

HZ

ZH(SHDN) ZH

Figure 8. Receiver Enable and Disable Times

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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

latch-up condition, which could destroy the device.

Traditionally RS485 transceivers have been designed us-

ing 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 latch-up.

Unfortunately, most bipolar devices draw a large amount

ofsupplycurrent, whichisunacceptableforthenumerous

applications that require low power consumption. The

LTC1483 is a CMOS RS485/RS422 transceiver which

features ultra-low power consumption without sacrificing

ESD and latch-up immunity.

V

CC

V

CC

SD3

P1

The LTC1483 uses a proprietary driver output stage,

which allows a common-mode range that extends beyond

thepowersupplieswhilevirtuallyeliminatinglatch-upand

providing excellent ESD protection. Figure 9 shows the

LTC1483 output stage while Figure 10 shows a conven-

tional CMOS output stage.

D1

OUTPUT

D2

LOGIC

SD4

N1

D2

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

LTC1483 • F10

LTC1483 • F09

Figure 9. LTC1483 Output Stage

Figure 10. Conventional

CMOS Output Stage

6

LTC1483

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APPLICATIO S I FOR ATIO

20

10

The LTC1483 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 diode

D1orD2stillturnson,butSD3orSD4willreversebiasand

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, latch-up is virtually eliminated under power-up or

power-down conditions.

0

–10

–20

–30

–40

–50

–60

–70

–80

0

1

2

3

4

5

FREQUENCY (MHz)

Figure 11. Typical RS485 Driver Output Spectrum

Transmitting at 150kHz

The LTC1483 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 well

beyond the RS485 operating range. An ESD cell protects

output against multiple ±10kV human body model ESD

strikes. Because the ESD injected current in the N-well or

substrate consists of majority carriers, latch-up is pre-

vented by careful layout techniques.

20

10

0

–10

–20

–30

–40

–50

–60

–70

–80

Slew Rate

The LTC1483 is designed for systems that are sensitive to

electromagnetic radiation. The part features a slew rate

limited driver that reduces high frequency electromag-

netic emissions, while improving signal fidelity by reduc-

ing reflections due to misterminated cables. Figures 11

and12showthespectrumofthesignalatthedriveroutput

for a standard slew rate RS485 driver and the slew rate

limited LTC1483. The LTC1483 shows significant reduc-

tion of the high frequency harmonics. Because the driver

is slew rate limited, the maximum operating frequency is

limited to 250kbits/s.

0

1

2

3

5

4

FREQUENCY (MHz)

Figure 12. Slew Rate Limited LTC1483 Driver Output

Spectrum Transmitting at 150kHz

drop to this 120µA level. With the driver enabled there will

be additional current drawn by the internal 12k resistor.

Under normal operating conditions this additional current

is overshadowed by the current drawn by the external bus

impedance.

Low Power Operation

The LTC1483 is designed to operate with a quiescent

currentof120µAmax.Withthedriverinthree-stateI_CCwill

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-

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

7

LTC1483

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APPLICATIO S I FOR ATIO

Shutdown Mode

than50nsthepartwillnotentershutdownmode. Toggling

either RE or DE will wake the LTC1483 back up within

3.5µs.

Both the receiver output (RO) and the driver outputs (A, B)

can be placed in three-state mode by bringing RE high and

DE low respectively. In addition, the LTC1483 will enter

shutdown mode when RE is high and DE is low.

If the slow slew rate driver was active immediately prior to

shutdown, the supply current will not drop to 1µA until the

driveroutputshavereachedasteadystate;thiscantakeas

long as 2.6µs under worst case conditions. If the driver

was disabled prior to shutdown the supply current will

drop to 1µA immediately.

In shutdown the LTC1483 typically draws only 1µA of

supply current. In order to guarantee that the part goes

into shutdown, RE must be high and DE must be low for

at least 600ns simultaneously. If this time duration is less

U

PACKAGE DESCRIPTION ^{Dimension in inches (millimeters) unless otherwise noted.}

N Package

8-Lead Plastic DIP

0.400*

(10.160)

MAX

0.130 ± 0.005

(3.302 ± 0.127)

0.300 – 0.325

(7.620 – 8.255)

0.045 – 0.065

(1.143 – 1.651)

8

7

6

5

4

0.065

(1.651)

TYP

0.009 – 0.015

(0.229 – 0.381)

0.255 ± 0.015*

(6.477 ± 0.381)

0.125

(3.175)

MIN

0.005

0.015

(0.380)

MIN

(0.127)

MIN

+0.025

–0.015

0.325

+0.635

8.255

1

2

3

(

)

–0.381

0.100 ± 0.010

(2.540 ± 0.254)

0.018 ± 0.003

(0.457 ± 0.076)

N8 0695

*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.

MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)

0.189 – 0.197*

(4.801 – 5.004)

S Package

8-Lead Plastic SOIC

7

5

8

6

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)

0.150 – 0.157**

(3.810 – 3.988)

0.228 – 0.244

(5.791 – 6.197)

0°– 8° TYP

0.016 – 0.050

0.406 – 1.270

0.050

(1.270)

BSC

0.014 – 0.019

(0.355 – 0.483)

*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH

SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

1

2

3

4

SO8 0695

**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD

FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE

RELATED PARTS

PART NUMBER

DESCRIPTION

COMMENTS

Low Power

LTC485

5V Low Power RS485 Interface Transceiver

3.3V Ultra-Low Power RS485 Transceiver

5V Ultra-Low Power RS485 Transceiver with Shutdown

5V Differential Bus Transceiver

LTC1480

LTC1481

LTC1485

LTC1487

World’s First 3V Powered 485 Transceiver with Low Power Consumption

Lowest Power

Highest Speed

5V Ultra-Low Power RS485 with Low EMI Shutdown

and High Input Impendance

High Input Impendance/Low EMI/Lowest Power

LT/GP 1094 10K • PRINTED IN THE USA

LINEAR TECHNOLOGY CORPORATION 1994

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7487

8

●

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


型号：	LT1483
厂家：	Linear
描述：	Ultra-Low Power RS485 Low EMI Transceiver with Shutdown 超低功耗低RS485收发器的电磁干扰具有关断状态
文件：	总8页 (文件大小：218K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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