505892X_技术文档

LT1083/LT1084/LT1085

7.5A, 5A, 3A Low Dropout

Positive Adjustable Regulators

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DESCRIPTIO

FEATURES

The LT^®1083 series of positive adjustable regulators are

designedtoprovide7.5A, 5Aand3Awithhigherefficiency

than currently available devices. All internal circuitry is

■

Three-Terminal Adjustable

■

Output Current of 3A, 5A or 7.5A

■

Operates Down to 1V Dropout

■

Guaranteed Dropout Voltage at Multiple Current Levels designed to operate down to 1V input-to-output differen-

■

Line Regulation: 0.015%

Load Regulation: 0.1%

100% Thermal Limit Functional Test

Fixed Versions Available

tial and the dropout voltage is fully specified as a function

of load current. Dropout is guaranteed at a maximum of

1.5Vatmaximumoutputcurrent, decreasingatlowerload

currents. On-chip trimming adjusts the reference voltage

to1%. Currentlimitisalsotrimmed, minimizingthestress

on both the regulator and power source circuitry under

overload conditions.

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APPLICATIO S

■

High Efficiency Linear Regulators

The LT1083/LT1084/LT1085 devices are pin compatible

with older three-terminal regulators. A 10µF output ca-

pacitor is required on these new devices. However, this is

included in most regulator designs.

■

Post Regulators for Switching Supplies

■

Constant Current Regulators

Battery Chargers

■

DEVICE

OUTPUT CURRENT*

Unlike PNP regulators, where up to 10% of the output

current is wasted as quiescent current, the LT1083 quies-

cent current flows into the load, increasing efficiency.

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

LT1083

LT1084

LT1085

7.5A

5.0A

3.0A

*For a 1.5A low dropout regulator see the LT1086 data sheet.

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TYPICAL APPLICATIO

5V, 7.5A Regulator

Dropout Voltage vs Output Current

2

LT1083

ADJ

5V AT 7.5A

OUT

V

IN

≥ 6.5V

IN

121Ω

1%

+

10µF

10µF*

TANTALUM

1

0

365Ω

1%

*REQUIRED FOR STABILITY

1083/4/5 ADJ TA01

0

I

FULL LOAD

OUTPUT CURRENT

1083/4/5 ADJ TA02

1

LT1083/LT1084/LT1085

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ABSOLUTE MAXIMUM RATINGS ^{(Note 1)}

Power Dissipation............................... Internally Limited

Input-to-Output Voltage Differential

“M” Grades: Control Section............. – 55°C to 150°C

Power Transistor .......... – 55°C to 200°C

“C” Grades .......................................................... 30V

“I” Grades............................................................ 30V

“M” Grades.......................................................... 35V

Operating Junction Temperature Range

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

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

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PRECO DITIO I G

“C” Grades: Control Section.................. 0°C to 125°C

Power Transistor ............... 0°C to 150°C

100% thermal shutdown functional test.

“I” Grades: Control Section............. – 40°C to 125°C

Power Transistor .......... – 40°C to 150°C

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PACKAGE/ORDER INFORMATION

TAB IS

FRONT VIEW

ORDER PART

NUMBER

ORDER PART

NUMBER

FRONT VIEW

OUTPUT

3

2

1

V

IN

TAB

IS

OUTPUT

3

2

1

V

IN

OUT

LT1084CT

LT1084IT

LT1085CT

LT1085IT

LT1083CP

LT1084CP

OUT

ADJ

T PACKAGE

3-LEAD PLASTIC TO-220

P PACKAGE

3-LEAD PLASTIC TO-3P

θ_JA= 50°C/W

θ_JA= 35°C/W

FRONT VIEW

BOTTOM VIEW

LT1083CK

LT1083MK

LT1084CK

LT1084MK

LT1085CK

LT1085MK

LT1085CM

3

2

1

V

CASE IS

OUTPUT

IN

OUT

V

IN

TAB

IS

OUTPUT

2

1

ADJ

M PACKAGE

3-LEAD PLASTIC DD

ADJ

θ_JA= 30°C/W*

K PACKAGE

*WITH PACKAGE SOLDERED TO 0.5IN²COPPER AREA

OVERBACKSIDEGROUNDPLANEORINTERNALPOWER

PLANE. θ_JACAN VARY FROM 20°C/W TO > 40°C/W

DEPENDING ON MOUNTING TECHNIQUE.

2-LEAD TO-3 METAL CAN

θ_JA= 35°C/W

ELECTRICAL CHARACTERISTICS ^The● denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at T_A= 25°C.

PARAMETER

CONDITIONS

= 10mA, T = 25°C,

MIN

TYP

MAX

UNITS

Reference Voltage

I

OUT

J

(V – V ) = 3V

1.238 1.250 1.262

1.225 1.250 1.270

V

IN

OUT

10mA ≤ I

≤ I

OUT

FULL LOAD

1.5V ≤ (V – V ) ≤ 25V (Notes 4, 6, 7)

●

IN

OUT

Line Regulation

I

= 10mA, 1.5V ≤ (V – V ) ≤ 15V, T = 25°C (Notes 2, 3)

0.015

0.035

0.05

0.2

0.5

%

LOAD

IN

OUT

J

●

M Grade: 15V ≤ (V – V ) ≤ 35V (Notes 2, 3)

C, I Grades: 15V ≤ (V – V ) ≤ 30V (Notes 2, 3)

IN

OUT

IN

OUT

2

LT1083/LT1084/LT1085

ELECTRICAL CHARACTERISTICS ^The● denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at T_A= 25°C.

PARAMETER

CONDITIONS

(V – V ) = 3V

MIN

TYP

MAX

UNITS

Load Regulation

IN

OUT

10mA ≤ I

T = 25°C (Notes 2, 3, 4, 6)

J

≤ I

OUT

FULL LOAD

0.1

0.2

1.3

0.3

0.4

1.5

%

V

●

Dropout Voltage

∆V = 1%, I

REF

= I (Notes 5, 6, 8)

FULLLOAD

OUT

Current Limit

LT1083

(V – V ) = 5V

●

8.0

0.4

5.5

0.3

3.2

0.2

9.5

1.0

6.5

0.6

4.0

0.5

A

IN

OUT

(V – V ) = 25V

IN

OUT

LT1084

LT1085

(V – V ) = 5V

IN OUT

(V – V ) = 25V

IN

OUT

(V – V ) = 5V

IN

OUT

(V – V ) = 25V

IN

OUT

Minimum Load Current

(V – V ) = 25V

●

5

10

mA

IN

OUT

Thermal Regulation

LT1083

T = 25°C, 30ms Pulse

A

0.002 0.010

0.003 0.015

0.004 0.020

%/W

LT1084

LT1085

Ripple Rejection

f = 120Hz, C

= 25µF, C

= 25µF Tantalum

ADJ

OUT

I

= I

FULL LOAD

, (V – V ) = 3V (Notes 6, 7, 8)

●

60

75

55

dB

µA

OUT

IN

OUT

Adjust Pin Current

T = 25°C

J

120

Adjust Pin Current Change

10mA ≤ I

1.5V ≤ (V – V ) ≤ 25V (Note 6)

≤ I

OUT FULL LOAD

●

0.2

0.5

0.3

5

1

µA

%

IN

OUT

Temperature Stability

Long Term Stability

T = 125°C, 1000 Hrs

A

RMS Output Noise (% of V

)

T = 25°C

10Hz = ≤ f ≤ 10kHz

OUT

A

0.003

%

Thermal Resistance Junction-to-Case

LT1083

Control Circuitry/Power Transistor

K Package

0.6/1.6

0.5/1.6

0.75/2.3

0.65/2.3

0.65/2.7

0.9/3.0

0.7/3.0

°C/W

P Package

K Package

P Package

T Package

K Package

M, T Packages

LT1084

LT1085

Note 1: Absolute Maximum Ratings are those values beyond which the life

of a device may be impaired.

Note 2: See thermal regulation specifications for changes in output voltage

due to heating effects. Load and line regulation are measured at a constant

junction temperature by low duty cycle pulse testing.

Note 4: I

is defined in the current limit curves. The I

FULL LOAD FULLLOAD

curve is defined as the minimum value of current limit as a function of

input-to-output voltage. Note that the 60W power dissipation for the

LT1083 (45W for the LT1084 (K, P), 30W for the LT1084 (T), 30W for the

LT1085) is only achievable over a limited range of input-to-output voltage.

Note 5: Dropout voltage is specified over the full output current range of

the device. Test points and limits are shown on the Dropout Voltage

curve.

Note 3: Line and load regulation are guaranteed up to the maximum power

dissapation (60W for the LT1083, 45W for the LT1084 (K, P), 30W for the

LT1084 (T) and 30W for the LT1085). Power dissipation is determined by

the input/output differential and the output current. Guaranteed maximum

power dissipation will not be available over the full input/output voltage

range.

Note 6: For LT1083 I

is 5A for –55°C ≤ T < – 40°C and 7.5A for

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FULL LOAD

T ≥ –40°C.

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Note 7: 1.7V ≤ (V – V ) ≤ 25V for LT1084 at –55°C ≤ T ≤ – 40°C.

IN

OUT

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Note 8: Dropout is 1.7V maximum for LT1084 at –55°C ≤ T ≤ –40°C.

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LT1083/LT1084/LT1085

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TYPICAL PERFORMANCE CHARACTERISTICS

LT1083

Dropout Voltage

LT1083

Short-Circut Current

LT1083

Load Regulation

12

10

8

0.10

0.05

2

INDICATES GUARANTEED TEST POINT

∆I = 7.5A

25°C

–40°C ≤ T ≤ 150°C

J

0°C ≤ T ≤ 125°C

J

150°C

0

–0.05

–0.10

–0.15

–0.20

6

1

T = 150°C

J

–55°C

4

2

0

T = 25°C

J

T = –55°C

J

I

FULL LOAD

GUARANTEED

10

INPUT/OUTPUT DIFFERENTIAL (V)

0

20

30

35

75 100

125 150

TEMPERATURE (°C)

0

5

15

25

–50 –25

0

25 50

0

1

2

3

4

5

6

7

8

9

10

OUTPUT CURRENT (A)

LT1083/4/5 ADJ G02

LT1083/4/5 ADJ G03

LT1083/4/5 ADJ G01

LT1084

Dropout Voltage

LT1084

Short-Circut Current

Load Regulation

10

9

8

7

6

5

4

3

2

1

0

2

0.10

0.05

INDICATES GUARANTEED TEST POINT

–55°C ≤ T ≤ 150°C

∆I = 5A

J

150°C

25°C

0°C ≤ T ≤ 125°C

J

0

–55°C

–0.05

–0.10

–0.15

–0.20

1

0

T

= –55°C

J

T

= 25°C

J

T

= 150°C

J

I

FULL LOAD

GUARANTEED

0

10

15

20

25

30

35

5

75 100

–50 –25

0

25 50

125 150

0

1

3

4

5

6

2

INPUT/OUTPUT DIFFERENTIAL (V)

TEMPERATURE (°C)

OUTPUT CURRENT (A)

LT1083/4/5 ADJ G05

LT1083/4/5 ADJ G06

LT1083/4/5 ADJ G04

LT1085

Dropout Voltage

LT1085

Short-Circut Current

Load Regulation

6

5

4

3

2

1

0

0.10

0.05

INDICATES GUARANTEED TEST POINT

∆I = 3A

–55°C ≤ T ≤ 150°C

J

0°C ≤ T ≤ 125°C

J

25°C

0

150°C

–0.05

–0.10

–0.15

–0.20

T = –55°C

J

–55°C

T = 25°C

J

2

1

0

T = 150°C

J

I

FULL LOAD

GUARANTEED

20

30

35

0

5

10

15

25

75 100

0

2

3

–50 –25

0

25 50

125 150

1

4

INPUT/OUTPUT DIFFERENTIAL (V)

TEMPERATURE (°C)

OUTPUT CURRENT (A)

LT1083/4/5 ADJ G08

LT1083/4/5 ADJ G07

LT1083/4/5 ADJ G09

4

LT1083/LT1084/LT1085

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TYPICAL PERFORMANCE CHARACTERISTICS

Minimum Operating Current

Temperature Stability

Adjust Pin Current

10

9

8

7

6

5

4

3

2

1

0

1.27

1.26

1.25

1.24

1.23

100

90

80

70

60

50

40

30

20

10

0

T = 150°C

J

T = 25°C

J

T = –55°C

J

0

10

15

20

25

30

35

–50 –25

0

25 50 75 100 125 150

TEMPERATURE (°C)

–50 –25

0

25 50 75 100 125 150

TEMPERATURE (°C)

5

INPUT/OUTPUT DIFFERENTIAL (V)

LT1083/4/5 ADJ G10

LT1083/4/5 ADJ G11

LT1083/4/5 ADJ G12

LT1083

Ripple Rejection

LT1083

Ripple Rejection vs Current

LT1083

Maximum Power Dissipation*

100

90

80

70

60

50

40

30

20

10

0

100

90

80

70

60

50

40

30

20

10

0

100

90

80

70

60

50

40

30

20

10

0

V

≤ 3V

P-P

V

RIPPLE

f

= 120Hz

RIPPLE

R

V

≤ 0.5V

≤ 3V

P-P

(V – V ) ≥ 3V

IN

OUT

f

= 20kHz

RIPPLE

R

V

≤ 0.5V

LT1083MK

P-P

(V – V ) ≥ V

IN

OUT

DROPOUT

LT1083CP

LT1083CK

C

I

= 200µF AT FREQUENCIES < 60Hz

= 25µF AT FREQUENCIES > 60Hz

= 7A

V

C

= 5V

= 25µF

ADJ

OUT

ADJ

OUT

10

100

1k

10k

100k

50 60 70 80 90 100 110 120 130 140 150

CASE TEMPERATURE (°C)

0

4

6

7

1

2

3

5

8

FREQUENCY (Hz)

OUTPUT CURRENT (A)

1083/4/5 ADJ G13

* AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE

1083/4/5 ADJ G14

LT1083/4/5 ADJ G15

LT1084

Ripple Rejection

LT1084

Ripple Rejection vs Current

LT1084

Maximum Power Dissipation*

100

90

80

70

60

50

40

30

20

10

0

60

100

90

80

70

60

50

40

30

20

10

0

f

= 120Hz

RIPPLE

V

≤ 3V

V

≤ 0.5V

R

RIPPLE

P-P

RIPPLE P-P

V

≤ 3V

P-P

50

(V – V ) ≥ 3V

IN

OUT

LT1084MK

f

= 20kHz

RIPPLE

R

40

V

≤ 0.5V

P-P

(V – V ) ≥ V

IN

OUT

DROPOUT

30

LT1084CT

LT1084CP

20

C

I

= 200µF AT FREQUENCIES < 60Hz

= 25µF AT FREQUENCIES > 60Hz

= 5A

V

OUT

C

ADJ

C

OUT

= 5V

= 25µF

ADJ

OUT

10

0

LT1084CK

10

100

1k

10k

100k

50 60 70 80 90 100 110 120 130 140 150

CASE TEMPERATURE (°C)

0

4

1

2

3

5

FREQUENCY (Hz)

OUTPUT CURRENT (A)

1083/4/5 ADJ G16

* AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE

1083/4/5 ADJ G17

LT1083/4/5 ADJ G18

5

LT1083/LT1084/LT1085

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TYPICAL PERFORMANCE CHARACTERISTICS

LT1085

Ripple Rejection

LT1085

Ripple Rejection vs Current

LT1085

Maximum Power Dissipation*

100

90

80

70

60

50

40

30

20

10

0

50

40

30

20

10

0

100

90

80

70

60

50

40

30

20

10

0

V

≤ 3V

P-P

V

RIPPLE

≤ 0.5V

P-P

f

= 120Hz

RIPPLE

R

(V – V ) ≥ 3V

IN

OUT

V

≤ 3V

P-P

LT1085MK

(V – V ) ≥ V

IN DROPOUT

f

V

= 20kHz

OUT

R

≤ 0.5V

RIPPLE

P-P

LT1085CT

LT1085CK

C

I

= 200µF AT FREQUENCIES < 60Hz

= 25µF AT FREQUENCIES > 60Hz

= 3A

V

= 5V

= 25µF

ADJ

OUT

ADJ

OUT

C

10

100

1k

10k

100k

50 60 70 80 90 100 110 120 130 140 150

CASE TEMPERATURE (°C)

0

2.5

0.5

1.0

1.5

2.0

3.0

FREQUENCY (Hz)

OUTPUT CURRENT (A)

1083/4/5 ADJ G19

* AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE

1083/4/5 ADJ G20

LT1083/4/5 ADJ G21

LT1083

Load Transient Response

LT1084

Load Transient Response

LT1085

Load Transient Response

0.6

0.4

0.2

0

0.6

0.3

C

ADJ

= 0

C

ADJ

= 0

0.4

0.2

0

0.2

0.1

0

C

= 0

ADJ

C

ADJ

= 1µF

C

= 1µF

C

= 1µF

ADJ

–0.2

–0.4

8

–0.2

–0.4

–0.6

6

–0.1

–0.2

–0.3

3

C

= 1µF

OUT

IN

C

= 1µF

OUT

= 10µF TANTALUM

IN

C

= 1µF

OUT

IN

= 10µF TANTALUM

V

=10V

OUT

IN

6

=13V

PRELOAD=100mA

V

=10V

OUT

V

=10V

4

OUT

IN

2

V

=13V

IN

=13V

2

1

PRELOAD=100mA

0

50

TIME (µs)

0

50

TIME (µs)

0

50

TIME (µs)

100

1083/4/5 ADJ G22

1083/4/5 ADJ G23

1083/4/5 ADJ G24

LT1083

LT1084

Line Transient Response

LT1085

Line Transient Response

60

40

60

40

150

100

50

C

= 0

C

= 0

C

ADJ

= 0

ADJ

C

ADJ

= 1µF

C

ADJ

= 1µF

C

ADJ

= 1µF

20

0

–20

–40

–60

14

–20

–40

–60

14

–50

–100

–150

14

V

IN

= 10V

V

IN

= 10V

V

IN

= 10V

OUT

I

= 0.2A

I

= 0.2A

I

= 0.2A

C

= 1µF TANTALUM

= 10µF TANTALUM

C

= 1µF TANTALUM

= 10µF TANTALUM

C

= 1µF TANTALUM

= 10µF TANTALUM

IN

OUT

IN

OUT

IN

OUT

13

12

0

100

TIME (µs)

0

100

TIME (µs)

0

100

TIME (µs)

200

1083/4/5 ADJ G26

1083/4/5 ADJ G27

1083/4/5 ADJ G25

6

LT1083/LT1084/LT1085

W

BLOCK DIAGRAM

V

IN

+

–

THERMAL

LIMIT

V

OUT

1083/4/5 ADJ BD

V

ADJ

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APPLICATIONS INFORMATION

The LT1083 family of three-terminal adjustable regulators

is easy to use and has all the protection features that are

expectedinhighperformancevoltageregulators. Theyare

short-circuit protected, and have safe area protection as

well as thermal shutdown to turn off the regulator should

the junction temperature exceed about 165°C.

theoutputwillensurestability.Normally,capacitorsmuch

smaller than this can be used with the LT1083. Many

different types of capacitors with widely varying charac-

teristics are available. These capacitors differ in capacitor

tolerance (sometimes ranging up to ±100%), equivalent

series resistance, and capacitance temperature coeffi-

cient. The 150µF or 22µF values given will ensure stability.

These regulators are pin compatible with older three-

terminal adjustable devices, offer lower dropout voltage

and more precise reference tolerance. Further, the refer-

ence stability with temperature is improved over older

types of regulators. The only circuit difference between

using the LT1083 family and older regulators is that this

new family requires an output capacitor for stability.

When the adjustment terminal is bypassed to improve the

ripple rejection, the requirement for an output capacitor

increases. The value of 22µF tantalum or 150µF aluminum

covers all cases of bypassing the adjustment terminal.

Without bypassing the adjustment terminal, smaller ca-

pacitors can be used with equally good results and the

table below shows approximately what size capacitors are

needed to ensure stability.

Stability

The circuit design used in the LT1083 family requires the

use of an output capacitor as part of the device frequency

compensation.Foralloperatingconditions,theadditionof

150µF aluminium electrolytic or a 22µF solid tantalum on

Recommended Capacitor Values

INPUT

OUTPUT

ADJUSTMENT

10µF

10µF Tantalum, 50µF Aluminum

22µF Tantalum, 150µF Aluminum

None

20µF

7

LT1083/LT1084/LT1085

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APPLICATIONS INFORMATION

Normally, capacitor values on the order of 100µF are used

in the output of many regulators to ensure good transient

responsewithheavyloadcurrentchanges. Outputcapaci-

tance can be increased without limit and larger values of

output capacitor further improve stability and transient

response of the LT1083 regulators.

input pin instantaneously shorted to ground, can damage

occur. A crowbar circuit at the input of the LT1083 can

generate those kinds of currents, and a diode from output

to input is then recommended. Normal power supply

cyclingorevenpluggingandunplugginginthesystemwill

not generate current large enough to do any damage.

Anotherpossiblestabilityproblemthatcanoccurinmono-

lithic IC regulators is current limit oscillations. These can

occur because, in current limit, the safe area protection

exhibits a negative impedance. The safe area protection

decreases the current limit as the input-to-output voltage

increases. That is the equivalent of having a negative

resistance since increasing voltage causes current to

decrease. Negative resistance during current limit is not

unique to the LT1083 series and has been present on all

power IC regulators. The value of the negative resistance

is a function of how fast the current limit is folded back as

input-to-output voltage increases. This negative resis-

tance can react with capacitors or inductors on the input

to cause oscillation during current limiting. Depending on

thevalueofseriesresistance, theoverallcircuitrymayend

up unstable. Since this is a system problem, it is not

necessarily easy to solve; however, it does not cause any

problemswiththeICregulatorandcanusuallybeignored.

The adjustment pin can be driven on a transient basis

±25V, with respect to the output without any device

degradation. Of course, as with any IC regulator, exceed-

ing the maximum input to output voltage differential

causes the internal transistors to break down and none of

the protection circuitry is functional.

D1

1N4002

(OPTIONAL)

IN

OUT

LT1083

ADJ

V

OUT

V

IN

+

C

OUT

150µF

R1

R2

+

C

ADJ

10µF

1083/4/5 ADJ F00

Overload Recovery

Like any of the IC power regulators, the LT1083 has safe

area protection. The safe area protection decreases the

current limit as input-to-output voltage increases and

keeps the power transistor inside a safe operating region

for all values of input-to-output voltage. The LT1083

protection is designed to provide some output current at

all values of input-to-output voltage up to the device

breakdown.

Protection Diodes

In normal operation, the LT1083 family does not need any

protection diodes. Older adjustable regulators required

protection diodes between the adjustment pin and the

output and from the output to the input to prevent over-

stressingthedie. TheinternalcurrentpathsontheLT1083

adjustmentpinarelimitedbyinternalresistors. Therefore,

even with capacitors on the adjustment pin, no protection

diodeisneededtoensuredevicesafetyundershort-circuit

conditions.

When power is first turned on, as the input voltage rises,

the output follows the input, allowing the regulator to start

up into very heavy loads. During the start-up, as the input

voltage is rising, the input-to-output voltage differential

remains small, allowing the regulator to supply large

output currents. With high input voltage, a problem can

occurwhereinremovalofanoutputshortwillnotallowthe

output voltage to recover. Older regulators, such as the

7800 series, also exhibited this phenomenon, so it is not

unique to the LT1083.

Diodes between input and output are usually not needed.

The internal diode between the input and the output pins

of the LT1083 family can handle microsecond surge

currents of 50A to 100A. Even with large output capaci-

tances, it is very difficult to get those values of surge

currents in normal operations. Only with a high value of

output capacitors, such as 1000µF to 5000µF and with the

8

LT1083/LT1084/LT1085

U

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APPLICATIONS INFORMATION

The problem occurs with a heavy output load when the

input voltage is high and the output voltage is low, such as

immediatelyafterremovalofashort.Theloadlineforsuch

aloadmayintersecttheoutputcurrentcurveattwopoints.

If this happens, there are two stable output operating

points for the regulator. With this double intersection, the

power supply may need to be cycled down to zero and

brought up again to make the output recover.

IN

OUT

LT1083

ADJ

V

OUT

V

IN

V

R1

R2

REF

I

ADJ

50µA

R2

R1

V

= V

1 +

+ I

R2

ADJ

OUT

REF

(

)

1083/4/5 ADJ F01

Figure 1. Basic Adjustable Regulator

Ripple Rejection

Load Regulation

The typical curves for ripple rejection reflect values for a

bypassed adjustment pin. This curve will be true for all

values of output voltage. For proper bypassing and ripple

rejectionapproachingthevaluesshown, theimpedanceof

the adjust pin capacitor at the ripple frequency should be

less than the value of R1, (normally 100Ω to 120Ω). The

size of the required adjust pin capacitor is a function of the

input ripple frequency. At 120Hz the adjust pin capacitor

should be 25µF if R1 = 100Ω. At 10kHz only 0.22µF is

needed.

Because the LT1083 is a three-terminal device, it is not

possible to provide true remote load sensing. Load regu-

lation will be limited by the resistance of the wire connect-

ing the regulator to the load. The data sheet specification

for load regulation is measured at the bottom of the

package. Negative side sensing is a true Kelvin connec-

tion, with the bottom of the output divider returned to the

negative side of the load. Although it may not be immedi-

ately obvious, best load regulation is obtained when the

top of the resistor divider R1 is connected directly to the

case not to the load. This is illustrated in Figure 2. If R1

were connected to the load, the effective resistance be-

tween the regulator and the load would be:

For circuits without an adjust pin bypass capacitor, the

ripple rejection will be a function of output voltage. The

output ripple will increase directly as a ratio of the output

voltage to the reference voltage (V_OUT/V_REF). For example,

with the output voltage equal to 5V and no adjust pin

capacitor,theoutputripplewillbehigherbytheratioof5V/

1.25V or four times larger. Ripple rejection will be de-

gradedby12dBfromthevalueshownonthetypicalcurve.

R2 +R1

R ×

, R = Parasitic Line Resistance

P

R1

R

P

PARASITIC

LINE RESISTANCE

Output Voltage

V

IN

LT1083 OUT

ADJ

IN

The LT1083 develops a 1.25V reference voltage between

the output and the adjust terminal (see Figure 1). By

placing a resistor R1 between these two terminals, a

constant current is caused to flow through R1 and down

through R2 to set the overall output voltage. Normally this

current is the specified minimum load current of 10mA.

Because I_ADJis very small and constant when compared

withthecurrentthroughR1,itrepresentsasmallerrorand

can usually be ignored.

R1*

R2*

R

L

*CONNECT R1 TO CASE

CONNECT R2 TO LOAD

1083/4/5 ADJ F02

Figure 2. Connections for Best Load Regulation

9

LT1083/LT1084/LT1085

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APPLICATIONS INFORMATION

Connected as shown, R_Pis not multiplied by the divider

ratio. R_Pis about 0.004Ω per foot using 16-gauge wire.

This translates to 4mV/ft at 1A load current, so it is

important to keep the positive lead between regulator and

load as short as possible and use large wire or PC board

traces.

compound at the case-to-heat sink interface is strongly

recommended. If the case of the device must be electri-

cally isolated, a thermally conductive spacer can be used,

as long as its added contribution to thermal resistance is

considered. Note that the case of all devices in this series

is electrically connected to the output.

For example, using an LT1083CK (TO-3, Commercial) and

assuming:

Thermal Considerations

The LT1083 series of regulators have internal power and

thermal limiting circuitry designed to protect the device

under overload conditions. For continuous normal load

conditions however, maximum junction temperature rat-

ings must not be exceeded. It is important to give careful

consideration to all sources of thermal resistance from

junction to ambient. This includes junction-to-case, case-

to-heat sink interface, and heat sink resistance itself. New

thermal resistance specifications have been developed to

more accurately reflect device temperature and ensure

safe operating temperatures. The data section for these

newregulatorsprovidesaseparatethermalresistanceand

maximum junction temperature for both the Control Sec-

tion and the Power Transistor. Previous regulators, with a

single junction-to-case thermal resistance specification,

used an average of the two values provided here and

therefore could allow excessive junction temperatures

under certain conditions of ambient temperature and heat

sink resistance. To avoid this possibility, calculations

should be made for both sections to ensure that both

thermal limits are met.

V_IN(max continuous) = 9V, V_OUT= 5V, I_OUT= 6A,

T_A= 75°C, θ_{HEAT SINK}= 1°C/W,

θ_{CASE-TO-HEAT SINK}= 0.2°C/W for K package with

thermal compound.

Power dissipation under these conditions is equal to:

P_D= (V_IN– V_OUT)(I_OUT) = 24W

Junction temperature will be equal to:

T_J= T_A+ P_D(θ_{HEAT SINK}+ θ_{CASE-TO-HEAT SINK}+ θ_JC)

For the Control Section:

T_J=75°C+24W(1°C/W+0.2°C/W+0.6°C/W)=118°C

118°C < 125°C = T_JMAX(Control Section

Commercial Range)

For the Power Transistor:

T_J=75°C+24W(1°C/W+0.2°C/W+1.6°C/W)=142°C

142°C < 150°C = T_JMAX(Power Transistor

Commercial Range)

In both cases the junction temperature is below the

maximum rating for the respective sections, ensuring

reliable operation.

Junction-to-case thermal resistance is specified from the

ICjunctiontothebottomofthecasedirectlybelowthedie.

This is the lowest resistance path for heat flow. Proper

mounting is required to ensure the best possible thermal

flowfromthisareaofthepackagetotheheatsink.Thermal

10

LT1083/LT1084/LT1085

U

TYPICAL APPLICATIONS

7.5A Variable Regulator

T1

L

1MH

TRIAD

C30B

F-269U

0V TO 35V

IN

LT1083 OUT

ADJ

OA TO 7.5A

+

20Ω

T2

750Ω* 1.5k

100µF

3

+

C1

50,000µF

110VAC

1N4003

LT1004-1.2

2

1

1N914

16k*

C30B

1N4003

2k

OUTPUT

ADJUST

1N4003

1µF

560Ω

15V

LT1004-1.2

2.7k

82k

10k

15k

16k*

–15V

4

8

200k

11k*

2

+

–

7

–15V

LT1011

3

0.1µF

1

1N4148

NC

100pF

15V

2N3904

8

–15V

4

3

1

–

+

7

3

8

LT1011

+

10k

6

2

LM301A

1% FILM RESISTOR

L: DALE TO-5 TYPE

*

1

2

–

7

15V

15K

15V

T2: STANCOR 11Z-2003

4

–15V

11k*

GENERAL PURPOSE REGULATOR WITH SCR PREREGULATOR

TO LOWER POWER DISSIPATION. ABOUT 1.7V DIFFERENTIAL

IS MAINTAINED ACROSS THE LT1083 INDEPENDENT OF OUTPUT

VOLTAGE AND LOAD CURRENT

LT1083/4/5 ADJ TA05

1µF

11

LT1083/LT1084/LT1085

U

TYPICAL APPLICATIONS

Paralleling Regulators

2 FEET #18 WIRE*

V

IN

LT1083 OUT

IN

ADJ

R2

R1

V

OUT

= 1.25V 1 +

(

)

I

= 0A TO 15A

OUT

0.015Ω

LT1083 OUT

ADJ

*THE #18 WIRE ACTS

AS BALLAST RESISTANCE

INSURING CURRENT SHARING

BETWEEN BOTH DEVICES

R1

120Ω

LT1083/4/5 ADJ TA03

R2

Improving Ripple Rejection

V

OUT

LT1083

ADJ

OUT

V

IN

5V

R1

121Ω

1%

+

10µF

150µF

R2

365Ω

1%

+

C1

25µF*

*C1 IMPROVES RIPPLE REJECTION.

SHOULD BE < R1 AT RIPPLE FREQUENCY

X

C

1083/4/5 ADJ TA04

Remote Sensing

R

P

(MAX DROP 300mV)

V

OUT

V

IN

LT1083 OUT

ADJ

IN

5V

+

V

IN

100µF

2

7

–

25Ω

6

LM301A

1k

3

+

1

+

121Ω

R

10µF

L

8

4

5µF

+

100pF

365Ω

RETURN

25Ω

RETURN

1083/4/5 ADJ TA07

12

LT1083/LT1084/LT1085

U

TYPICAL APPLICATIONS

High Efficiency Regulator with Switching Preregulator

1mH

V

IN

LT1083 OUT

ADJ

V

OUT

28V

+

MR1122

10,000µF

240Ω

470Ω

1N914

10k

2k

28V

1k

1M

4N28

10k

+

1083/4/5 ADJ TA06

LT1011

28V

–

1N914

1.2V to 15V Adjustable Regulator

†

V

LT1083 OUT

ADJ

V

OUT

IN

R1

90.9Ω

+

C1*

10µF

C2

100µF

R2

1k

*NEEDED IF DEVICE IS FAR FROM FILTER CAPACITORS

†

R2

R1

V

= 1.25V 1 +

OUT

1083/4/5 ADJ TA08

(

)

5V Regulator with Shutdown*

V

OUT

LT1083

ADJ

V

OUT

IN

5V

121Ω

1%

+

10µF

1k

+

100µF

365Ω

1%

2N3904

TTL

1k

1083/4/5 ADJ TA09

*OUTPUT SHUTS DOWN TO 1.3V

13

LT1083/LT1084/LT1085

U

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

K Package

2-Lead TO-3 Metal Can

(LTC DWG # 05-08-1310)

0.760 – 0.775

(19.30 – 19.69)

0.320 – 0.350

(8.13 – 8.89)

0.060 – 0.135

(1.524 – 3.429)

0.420 – 0.480

(10.67 – 12.19)

0.038 – 0.043

(0.965 – 1.09)

1.177 – 1.197

(29.90 – 30.40)

0.655 – 0.675

(16.64 – 17.15)

0.210 – 0.220

(5.33 – 5.59)

0.151 – 0.161

(3.86 – 4.09)

DIA, 2PLCS

0.167 – 0.177

(4.24 – 4.49)

R

0.425 – 0.435

(10.80 – 11.05)

0.067 – 0.077

(1.70 – 1.96)

0.490 – 0.510

(12.45 – 12.95)

R

K2 (TO-3) 1098

M Package

3-Lead Plastic DD Pak

(LTC DWG # 05-08-1460)

0.060

(1.524)

TYP

0.390 – 0.415

(9.906 – 10.541)

0.060

(1.524)

0.165 – 0.180

(4.191 – 4.572)

0.256

(6.502)

0.045 – 0.055

(1.143 – 1.397)

15° TYP

+0.008

0.004

–0.004

0.060

(1.524)

0.059

(1.499)

TYP

0.183

(4.648)

0.330 – 0.370

(8.382 – 9.398)

+0.203

–0.102

0.102

(

)

0.095 – 0.115

(2.413 – 2.921)

0.075

(1.905)

0.090 – 0.110

(2.286 – 2.794)

0.050 ± 0.012

(1.270 ± 0.305)

0.300

(7.620)

+0.012

0.143

0.013 – 0.023

(0.330 – 0.584)

–0.020

0.050

(1.270)

BSC

+0.305

3.632

BOTTOM VIEW OF DD PAK

HATCHED AREA IS SOLDER PLATED

COPPER HEAT SINK

(

)

–0.508

M (DD3) 1098

14

LT1083/LT1084/LT1085

U

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

P Package

3-Lead Plastic TO-3P (Similar to TO-247)

(LTC DWG # 05-08-1450)

0.560

0.187 – 0.207

(4.75 – 5.26)

(14.224)

0.620 – 0.64O

(15.75 – 16.26)

0.325

(8.255)

0.275

(6.985)

0.060 – 0.080

(1.52 – 2.03)

MOUNTING HOLE

0.115 – 0.145

(2.92 – 3.68)

DIA

18° – 22°

0.580

(14.732)

0.830 – 0.870

0.170 – 0.2OO

(21.08 – 22.10)

(4.32 – 5.08)

0.700

(17.780)

EJECTOR PIN MARKS

0.105 – 0.125

(2.67 – 3.18)

DIA

0.580 – 0.6OO

(14.73 – 15.24)

0.098

(2.489)

3° – 7°

0.170

(4.32)

MAX

0.124

(3.149)

0.780 – 0.800

(19.81 – 20.32)

0.042 – 0.052

(1.07 – 1.32)

0.215

(5.46)

BSC

0.087 – 0.102

(2.21 – 2.59)

BOTTOM VIEW OF TO-3P

HATCHED AREA IS SOLDER PLATED

COPPER HEAT SINK

0.020 – 0.040

(0.51 – 1.02)

P3 0996

0.074 – 0.084

(1.88 – 2.13)

0.113 – 0.123

(2.87 – 3.12)

T Package

3-Lead Plastic TO-220

(LTC DWG # 05-08-1420)

0.147 – 0.155

(3.734 – 3.937)

DIA

0.165 – 0.180

(4.191 – 4.572)

0.390 – 0.415

(9.906 – 10.541)

0.045 – 0.055

(1.143 – 1.397)

0.230 – 0.270

(5.842 – 6.858)

0.570 – 0.620

0.460 – 0.500

(14.478 – 15.748)

(11.684 – 12.700)

0.330 – 0.370

(8.382 – 9.398)

0.980 – 1.070

(24.892 – 27.178)

0.520 – 0.570

(13.208 – 14.478)

0.218 – 0.252

(5.537 – 6.401)

0.013 – 0.023

(0.330 – 0.584)

0.100

(2.540)

BSC

0.095 – 0.115

(2.413 – 2.921)

0.050

(1.270)

TYP

0.028 – 0.038

(0.711 – 0.965)

T3 (TO-220) 1098

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.

15

LT1083/LT1084/LT1085

U

TYPICAL APPLICATIONS

Automatic Light Control

LT1083

ADJ

V

OUT

IN

1.2k

+

100µF

10µF

1083/4/5 ADJ TA10

Protected High Current Lamp Driver

12V

5A

LT1083

ADJ

15V

IN

OUT

TTL OR

CMOS

1083/4/5 ADJ TA11

10k

RELATED PARTS

PART NUMBER

DESCRIPTION

COMMENTS

LT1086

1.5A Low Dropout Regulator

800mA Low Dropout Regulator

Fixed 2.85V, 3.3V, 3.6V, 5V and 12V Output

Fixed 2.85V, 3.3V, 5V or Adjustable Output

For High Performance Microprocessors

LT1117

LT1584/LT1585/LT1587 7A/4.6A/3A Fast Response Low Dropout Regulators

LT1580

LT1581

LT1430

LT1575

LT1573

7A Very Low Dropout Linear Regulator

0.54V Dropout at 7A, Fixed 2.5V

and Adjustable

OUT

10A Very Low Dropout Linear Regulator

High Power Step-Down Switching Regulator

UltraFast^TMTransient Response LDO Controller

UltraFast Transient Response LDO Controller

0.43V Dropout at 10A, Fixed 2.5V

and Adjustable

OUT

5V to 3.3V at 10A, >90% Efficiency

External MOSFET Pass Element

External PNP Pass Element

UltraFast is a trademark of Linear Technology Corporation.

108345fd LT/TP 0200 2K REV D • PRINTED IN USA

LINEAR TECHNOLOGY CORPORATION 1994

16 ^{LinearTechnology Corporation}

1630 McCarthy Blvd., Milpitas, CA 95035-7417

●

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


型号：	505892X
厂家：	ETC
描述：	IC IC内部から
文件：	总16页 (文件大小：282K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

505892X [ETC]

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