Linear Technology LT1085IT, LT1084MK, LT1084IT, LT1085CT, LT1085CM Datasheet

FEATURES

■

Three-Terminal Adjustable

■

Output Current of 3A, 5A or 7.5A

■

Operates Down to 1V Dropout

■

Guaranteed Dropout Voltage at Multiple Current Levels

■

Line Regulation: 0.015%

■

Load Regulation: 0.1%

■

100% Thermal Limit Functional Test

■

Fixed Versions Available

U

APPLICATIO S

■

High Efficiency Linear Regulators

■

Post Regulators for Switching Supplies

■

Constant Current Regulators

■

Battery Chargers

DEVICE OUTPUT CURRENT*

LT1083 7.5A
LT1084 5.0A
LT1085 3.0A

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

LT1083/LT1084/LT1085

7.5A, 5A, 3A Low Dropout

Positive Adjustable Regulators

U

DESCRIPTIO

The LT®1083 series of positive adjustable regulators are
designed to provide 7.5A, 5A and 3A with higher efficiency
than currently available devices. All internal circuitry is
designed to operate down to 1V input-to-output differen­tial and the dropout voltage is fully specified as a function
of load current. Dropout is guaranteed at a maximum of

1.5V at maximum output current, decreasing at lower load
currents. On-chip trimming adjusts the reference voltage
to 1%. Current limit is also trimmed, minimizing the stress
on both the regulator and power source circuitry under
overload conditions.

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.

Unlike PNP regulators, where up to 10% of the output
current is wasted as quiescent current, the LT1083 quies­cent current flows into the load, increasing efficiency.

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

TYPICAL APPLICATIO

5V, 7.5A Regulator

V

≥ 6.5V

IN

+

10µF

*REQUIRED FOR STABILITY

LT1083

IN

OUT

ADJ

U

121Ω
1%

365Ω
1%

+

5V AT 7.5A

10µF*
TANTALUM

1083/4/5 ADJ TA01

Dropout Voltage vs Output Current

2

1

INPUT/OUTPUT VOLTAGE DIFFERENTIAL (V)

0

0

OUTPUT CURRENT

I

FULL LOAD

1083/4/5 ADJ TA02

1

LT1083/LT1084/LT1085

WW

W

ABSOLUTE MAXIMUM RATINGS

U

(Note 1)

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

Input-to-Output Voltage Differential

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

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

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

Operating Junction Temperature Range

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

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

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

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

U

W

U

PACKAGE/ORDER INFORMATION

TAB

OUTPUT

FRONT VIEW

3

IS

3-LEAD PLASTIC TO-220

T PACKAGE

= 50°C/W

θ

JA

2

1

V

V

ADJ

IN

OUT

ORDER PART

NUMBER

LT1084CT
LT1084IT
LT1085CT
LT1085IT

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

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

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

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

UUU

PRECO DITIO I G

100% thermal shutdown functional test.

TAB IS

OUTPUT

3-LEAD PLASTIC TO-3P

FRONT VIEW

3

2

1

P PACKAGE

θJA = 35°C/W

V

V

ADJ

IN

OUT

ORDER PART

NUMBER

LT1083CP
LT1084CP

BOTTOM VIEW

V

IN

2

CASE IS
OUTPUT

LT1083CK
LT1083MK
LT1084CK
LT1084MK

1

LT1085CK
LT1085MK

ADJ

K PACKAGE

2-LEAD TO-3 METAL CAN

θJA = 35°C/W

ELECTRICAL CHARACTERISTICS

TAB

IS

OUTPUT

*WITH PACKAGE SOLDERED TO 0.5IN2 COPPER AREA

OVER BACKSIDE GROUND PLANE OR INTERNAL POWER
PLANE. θ

JA

DEPENDING ON MOUNTING TECHNIQUE.

The ● denotes the specifications which apply over the full operating

FRONT VIEW

3

3

2

2

1

1

M PACKAGE

3-LEAD PLASTIC DD

θ

= 30°C/W*

JA

CAN VARY FROM 20°C/W TO > 40°C/W

V

V

ADJ

IN

OUT

LT1085CM

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

PARAMETER CONDITIONS MIN TYP MAX UNITS

Reference Voltage I

Line Regulation I

= 10mA, TJ = 25°C,

OUT

– V

(V

IN

10mA ≤ I

1.5V ≤ (VIN – V

LOAD

M Grade: 15V ≤ (VIN – V
C, I Grades: 15V ≤ (VIN – V

) = 3V 1.238 1.250 1.262 V

OUT

≤ I

OUT

FULL LOAD

) ≤ 25V (Notes 4, 6, 7) ● 1.225 1.250 1.270 V

OUT

= 10mA, 1.5V ≤ (VIN – V

OUT

) ≤ 15V, TJ = 25°C (Notes 2, 3) 0.015 0.2 %

OUT

) ≤ 35V (Notes 2, 3) ● 0.05 0.5 %

) ≤ 30V (Notes 2, 3) ● 0.05 0.5 %

OUT

● 0.035 0.2 %

2

LT1083/LT1084/LT1085

ELECTRICAL CHARACTERISTICS

The ● denotes the specifications which apply over the full operating

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

PARAMETER CONDITIONS MIN TYP MAX UNITS

Load Regulation (VIN – V

10mA ≤ I
TJ = 25°C (Notes 2, 3, 4, 6) 0.1 0.3 %

Dropout Voltage ∆V
Current Limit

LT1083 (V

LT1084 (V

LT1085 (V

(V

(V

IN
IN
IN
IN
IN

(VIN – V
Minimum Load Current (VIN – V
Thermal Regulation TA = 25°C, 30ms Pulse

LT1083 0.002 0.010 %/W
LT1084 0.003 0.015 %/W
LT1085 0.004 0.020 %/W

Ripple Rejection f = 120Hz, C

I

OUT

Adjust Pin Current T

= 25°C55µA

J

Adjust Pin Current Change 10mA ≤ I

1.5V ≤ (VIN – V

Temperature Stability ● 0.5 %
Long Term Stability TA = 125°C, 1000 Hrs 0.3 1 %
RMS Output Noise (% of V

)T

OUT

= 25°C

A

10Hz = ≤ f ≤ 10kHz 0.003 %
Thermal Resistance Junction-to-Case Control Circuitry/Power Transistor

LT1083 K Package 0.6/1.6 °C/W
LT1084 K Package 0.75/2.3 °C/W

LT1085 K Package 0.9/3.0 °C/W

) = 3V

OUT

≤ I

OUT

FULL LOAD

● 0.2 0.4 %

REF

– V
– V
– V
– V
– V

= I

= 1%, I

OUT
OUT
OUT
OUT
OUT
OUT

OUT

FULL LOAD

OUT

= I

FULLLOAD

(Notes 5, 6, 8) ● 1.3 1.5 V

) = 5V ● 8.0 9.5 A
) = 25V ● 0.4 1.0 A
) = 5V ● 5.5 6.5 A
) = 25V ● 0.3 0.6 A
) = 5V ● 3.2 4.0 A
) = 25V ● 0.2 0.5 A

) = 25V ● 510 mA

OUT

= 25µF, C

ADJ

, (VIN – V

≤ I

FULL LOAD

) ≤ 25V (Note 6) ● 0.2 5 µA

OUT

= 25µF Tantalum

OUT

) = 3V (Notes 6, 7, 8) ● 60 75 dB

OUT

● 120 µA

P Package 0.5/1.6 °C/W
P Package 0.65/2.3 °C/W

T Package 0.65/2.7 °C/W
M, T Packages 0.7/3.0 °C/W

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 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 4: I

FULL LOAD

is defined in the current limit curves. The I

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 6: For LT1083 I

≥ –40°C.

T

J

FULL LOAD

Note 7: 1.7V ≤ (VIN – V
Note 8: Dropout is 1.7V maximum for LT1084 at –55°C ≤ T

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

) ≤ 25V for LT1084 at –55°C ≤ TJ ≤ –40°C.

OUT

≤ –40°C.

J

3

LT1083/LT1084/LT1085

W

U

TYPICAL PERFORMANCE CHARACTERISTICS

LT1083 LT1083 LT1083
Dropout Voltage Short-Circut Current Load Regulation

2

INDICATES GUARANTEED TEST POINT

–40°C ≤ TJ ≤ 150°C

0°C ≤ TJ ≤ 125°C

12

10

8

25°C

150°C

0.10

∆I = 7.5A

0.05

0

1

MINIMUM INPUT/OUTPUT DIFFERENTIAL (V)

0

12345678910

0

TJ = 150°C

TJ = 25°C

TJ = –55°C

OUTPUT CURRENT (A)

LT1083/4/5 ADJ G01

6

–55°C

4

SHORT-CIRCUIT CURRENT (A)

2

I

FULL LOAD

GUARANTEED

0

0

510

INPUT/OUTPUT DIFFERENTIAL (V)

15 25

20 30 35

LT1083/4/5 ADJ G02

–0.05

–0.10

–0.15

OUTPUT VOLTAGE DEVIATION (%)

–0.20

–50

–25 25

LT1084 LT1084 LT1084
Dropout Voltage Short-Circut Current Load Regulation

2

INDICATES GUARANTEED TEST POINT

–55°C ≤ TJ ≤ 150°C

0°C ≤ TJ ≤ 125°C

1

TJ = 150°C

MINIMUN INPUT/OUTPUT DIFFERENTIAL (V)

0

0

TJ = 25°C

1

2

OUTPUT CURRENT (A)

TJ = –55°C

34

LT1083/4/5 ADJ G04

5

6

10

9
8
7

6

5
4
3
2

SHORT-CIRCUIT CURRENT (A)

1

GUARANTEED

0

0

150°C

I

FULL LOAD

15

10

5
INPUT/OUTPUT DIFFERENTIAL (V)

25°C

–55°C

0.10

∆I = 5A

0.05

0

–0.05

–0.10

–0.15

OUTPUT VOLTAGE DEVIATION (%)

20

25

30

LT1083/4/5 ADJ G05

35

–0.20

–50

–25 25

050

TEMPERATURE (°C)

050

TEMPERATURE (°C)

75

75

100

125

LT1083/4/5 ADJ G03

100

125

LT1083/4/5 ADJ G06

150

150

LT1085 LT1085 LT1085
Dropout Voltage Short-Circut Current Load Regulation

2

INDICATES GUARANTEED TEST POINT

–55°C ≤ TJ ≤ 150°C

0°C ≤ TJ ≤ 125°C

1

TJ = 150°C

MINIMUM INPUT/OUTPUT DIFFERENTIAL (V)

0

0

TJ = 25°C

1

2

OUTPUT CURRENT (A)

TJ = –55°C

3

LT1083/4/5 ADJ G07

4

6

5

4

3

–55°C

2

I

SHORT-CIRCUIT CURRENT (A)

FULL LOAD

1

GUARANTEED

0

0

510

INPUT/OUTPUT DIFFERENTIAL (V)

25°C
150°C

15 25

20 30 35

LT1083/4/5 ADJ G08

0.10

∆I = 3A

0.05

0

–0.05

–0.10

–0.15

OUTPUT VOLTAGE DEVIATION (%)

–0.20

–50

4

–25 25

050

TEMPERATURE (°C)

75

100

125

LT1083/4/5 ADJ G09

150

LT1083/LT1084/LT1085

CASE TEMPERATURE (°C)

50

POWER (W)

100

90
80
70
60
50
40
30
20
10

0

LT1083/4/5 ADJ G15

60 70 80 90 100 110 120 130 140 150

LT1083MK

LT1083CP

LT1083CK

* AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE

CASE TEMPERATURE (°C)

50

POWER (W)

60

50

40

30

20

10

0

LT1083/4/5 ADJ G18

60 70 80 90 100 110 120 130 140 150

LT1084MK

LT1084CT

LT1084CP

* AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE

LT1084CK

W

U

TYPICAL PERFORMANCE CHARACTERISTICS

Minimum Operating Current Temperature Stability Adjust Pin Current

10

9
8
7
6
5
4

TJ = 25°C

3
2
1

MINIMUM OPERATING CURRENT (mA)

0

0

TJ = –55°C

10

5

INPUT/OUTPUT DIFFERENTIAL (V)

15

TJ = 150°C

20

25

LT1083/4/5 ADJ G10

35

30

LT1083 LT1083 LT1083
Ripple Rejection Ripple Rejection vs Current Maximum Power Dissipation*

100

90
80
70
60
50
40
30

RIPPLE REJECTION (dB)

20
10

0

V

≤ 3V

RIPPLE

(VIN – V

OUT

C

= 200µF AT FREQUENCIES < 60Hz

ADJ

= 25µF AT FREQUENCIES > 60Hz

C

ADJ

= 7A

I

OUT

10 1k 10k 100k

100

P-P

) ≥ V

DROPOUT

FREQUENCY (Hz)

(VIN – V

V

RIPPLE

≤ 0.5V

) ≥ 3V

OUT

1083/4/5 ADJ G13

P-P

1.27

1.26

1.25

1.24

REFERENCE VOLTAGE (V)

1.23
–50

100

90
80
70
60
50
40
30

RIPPLE REJECTION (dB)

20
10

0

0

050

–25 25

TEMPERATURE (°C)

fR = 20kHz

≤ 0.5V

V

RIPPLE

V

= 5V

OUT

= 25µF

C

ADJ

= 25µF

C

OUT

13

2

OUTPUT CURRENT (A)

P-P

fR = 120Hz
V

RIPPLE

4

75

5

100

125

LT1083/4/5 ADJ G11

≤ 3V

P-P

7

6

1083/4/5 ADJ G14

150

100

90
80
70
60
50
40
30

ADJUST PIN CURRENT (µA)

20
10

0

–50

8

050

–25 25

TEMPERATURE (°C)

75

100

125

LT1083/4/5 ADJ G12

150

LT1084 LT1084 LT1084
Ripple Rejection Ripple Rejection vs Current Maximum Power Dissipation*

100

V

90
80
70
60

(VIN – V

50
40
30

RIPPLE REJECTION (dB)

C

= 200µF AT FREQUENCIES < 60Hz

20

ADJ

= 25µF AT FREQUENCIES > 60Hz

C

ADJ

10

= 5A

I

OUT

0

10 1k 10k 100k

≤ 3V

RIPPLE

) ≥ V

OUT

100

FREQUENCY (Hz)

P-P

DROPOUT

V

RIPPLE

(VIN – V

≤ 0.5V

) ≥ 3V

OUT

1083/4/5 ADJ G16

P-P

100

90
80

fR = 20kHz

70
60
50
40
30

RIPPLE REJECTION (dB)

20
10

0

≤ 0.5V

V

RIPPLE

V

= 5V

OUT

= 25µF

C

ADJ

= 25µF

C

OUT

0

13

OUTPUT CURRENT (A)

P-P

2

fR = 120Hz

≤ 3V

V

RIPPLE

P-P

4

1083/4/5 ADJ G17

5

5

LT1083/LT1084/LT1085

CASE TEMPERATURE (°C)

50

POWER (W)

50

40

30

20

10

0

LT1083/4/5 ADJ G21

60 70 80 90 100 110 120 130 140 150

LT1085MK

LT1085CT

LT1085CK

* AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE

W

U

TYPICAL PERFORMANCE CHARACTERISTICS

LT1085 LT1085 LT1085
Ripple Rejection Ripple Rejection vs Current Maximum Power Dissipation*

100

90
80
70
60
50
40
30

RIPPLE REJECTION (dB)

20
10

0

V

≤ 3V

RIPPLE

(VIN – V

C

= 200µF AT FREQUENCIES < 60Hz

ADJ

= 25µF AT FREQUENCIES > 60Hz

C

ADJ

= 3A

I

OUT

10 1k 10k 100k

100

P-P

) ≥ V

OUT

DROPOUT

FREQUENCY (Hz)

V
≤ 0.5V

(VIN – V

RIPPLE

P-P

) ≥ 3V

OUT

1083/4/5 ADJ G19

LT1083 LT1084 LT1085
Load Transient Response Load Transient Response Load Transient Response

0.6

0.4

0.2
0

–0.2

DEVIATION (V)

OUTPUT VOLTAGE

–0.4

8
6
4
2

LOAD CURRENT (A)

0

0

C

= 0

ADJ

CIN = 1µF

= 10µF TANTALUM

C

OUT

50

TIME (µs)

C

= 1µF

ADJ

V

=10V

OUT

=13V

V

IN

PRELOAD= 100mA

1083/4/5 ADJ G22

100

90
80
70
60
50
40
30

RIPPLE REJECTION (dB)

20
10

0

0.6

0.4

0.2

–0.2

DEVIATION (V)

OUTPUT VOLTAGE

–0.4
–0.6

LOAD CURRENT (A)

100

fR = 120Hz

≤ 3V

V

RIPPLE

fR = 20kHz
V

RIPPLE

V

OUT

C

ADJ

C

OUT

0

0

6
4
2
0

0

P-P

≤ 0.5V

= 5V

= 25µF

= 25µF

0.5 2.0

1.0 1.5

OUTPUT CURRENT (A)

CIN = 1µF
C

OUT

P-P

C

= 0

ADJ

= 10µF TANTALUM

V

OUT

=13V

V

IN

PRELOAD=100mA

50

TIME (µs)

2.5

1083/4/5 ADJ G20

C

= 1µF

ADJ

=10V

1083/4/5 ADJ G23

3.0

100

0.3

0.2

0.1
0

–0.1

DEVIATION (V)

OUTPUT VOLTAGE

–0.2
–0.3

3
2
1
0

LOAD CURRENT (A)

0

C

= 0

ADJ

CIN = 1µF

= 10µF TANTALUM

C

OUT

TIME (µs)

V

=10V

OUT

V

=13V

IN

PRELOAD=100mA

50

C

ADJ

1083/4/5 ADJ G24

= 1µF

100

LT1083 LT1084 LT1085
Line Transient Response Line Transient Response Line Transient Response

150

C

= 0

0

0

ADJ

V

= 10V

OUT

= 0.2A

I

IN

= 1µF TANTALUM

C

IN

= 10µF TANTALUM

C

OUT

100

TIME (µs)

100

50

–50

DEVIATION (mV)

OUTPUT VOLTAGE

–100
–150

14
13

INPUT

12

DEVIATION (V)

6

C

ADJ

1083/4/5 ADJ G25

= 1µF

OUTPUT VOLTAGE

INPUT

200

60

C

40
20

0

–20

DEVIATION (V)

–40
–60

14
13
12

DEVIATION (V)

0

ADJ

= 0

C

= 1µF

ADJ

V

OUT

= 0.2A

I

IN

= 1µF TANTALUM

C

IN

C

OUT

100

TIME (µs)

= 10V

= 10µF TANTALUM

1083/4/5 ADJ G26

OUTPUT VOLTAGE

INPUT

200

60

C

40

ADJ

20

0

–20

DEVIATION (mV)

–40
–60

14
13
12

DEVIATION (V)

0

= 0

V

= 10V

OUT

= 0.2A

I

IN

= 1µF TANTALUM

C

IN

= 10µF TANTALUM

C

OUT

100

TIME (µs)

C

= 1µF

ADJ

1083/4/5 ADJ G27

200

BLOCK DIAGRAM

W

THERMAL

LIMIT

LT1083/LT1084/LT1085

V

IN

+

–

V

OUT

V

ADJ

U

WUU

APPLICATIONS INFORMATION

The LT1083 family of three-terminal adjustable regulators
is easy to use and has all the protection features that are
expected in high performance voltage regulators. They are
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.

These regulators are pin compatible with older three­terminal adjustable devices, offer lower dropout voltage
and more precise reference tolerance. Further, the refer­ence 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.

Stability

1083/4/5 ADJ BD

the output will ensure stability. Normally, capacitors much
smaller than this can be used with the LT1083. Many
different types of capacitors with widely varying charac­teristics are available. These capacitors differ in capacitor
tolerance (sometimes ranging up to ±100%), equivalent
series resistance, and capacitance temperature coeffi­cient. The 150µF or 22µF values given will ensure 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 ca­pacitors can be used with equally good results and the
table below shows approximately what size capacitors are
needed to ensure stability.

The circuit design used in the LT1083 family requires the
use of an output capacitor as part of the device frequency
compensation. For all operating conditions, the addition of
150µF aluminium electrolytic or a 22µF solid tantalum on

Recommended Capacitor Values

INPUT OUTPUT ADJUSTMENT

10µF10µF Tantalum, 50µF Aluminum None
10µF22µF Tantalum, 150µF Aluminum 20µF

7

LT1083/LT1084/LT1085

U

WUU

APPLICATIONS INFORMATION

Normally, capacitor values on the order of 100µF are used
in the output of many regulators to ensure good transient
response with heavy load current changes. Output capaci­tance can be increased without limit and larger values of
output capacitor further improve stability and transient
response of the LT1083 regulators.

Another possible stability problem that can occur in mono­lithic 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 resis­tance can react with capacitors or inductors on the input
to cause oscillation during current limiting. Depending on
the value of series resistance, the overall circuitry may end
up unstable. Since this is a system problem, it is not
necessarily easy to solve; however, it does not cause any
problems with the IC regulator and can usually be ignored.

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
cycling or even plugging and unplugging in the system will
not generate current large enough to do any damage.

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, exceed­ing 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

V

IN

LT1083

ADJ

+

C

ADJ

10µF

R1

R2

+

1083/4/5 ADJ F00

V

C

OUT

150µF

OUT

Overload Recovery

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 over­stressing the die. The internal current paths on the LT1083
adjustment pin are limited by internal resistors. Therefore,
even with capacitors on the adjustment pin, no protection
diode is needed to ensure device safety under short-circuit
conditions.

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 capaci­tances, 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

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.

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
occur wherein removal of an output short will not allow the
output voltage to recover. Older regulators, such as the
7800 series, also exhibited this phenomenon, so it is not
unique to the LT1083.

8

LT1083/LT1084/LT1085

U

WUU

APPLICATIONS INFORMATION

The problem occurs with a heavy output load when the
input voltage is high and the output voltage is low, such as
immediately after removal of a short. The load line for such
a load may intersect the output current curve at two points.
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.

Ripple Rejection

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
rejection approaching the values shown, the impedance of
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.

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/VREF

with the output voltage equal to 5V and no adjust pin
capacitor, the output ripple will be higher by the ratio of 5V/

1.25V or four times larger. Ripple rejection will be de­graded by 12dB from the value shown on the typical curve.

Output Voltage

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

is very small and constant when compared

ADJ

with the current through R1, it represents a small error and
can usually be ignored.

). For example,

IN OUT

V

IN

V

OUT

Figure 1. Basic Adjustable Regulator

LT1083

ADJ

I

ADJ

50µA

= V

R2

1 + + I

REF

( )

R1

ADJ

R2

V

REF

R1

R2

1083/4/5 ADJ F01

V

OUT

Load Regulation

Because the LT1083 is a three-terminal device, it is not
possible to provide true remote load sensing. Load regu­lation will be limited by the resistance of the wire connect­ing 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 connec­tion, with the bottom of the output divider returned to the
negative side of the load. Although it may not be immedi­ately obvious, best load regulation is obtained when the
top of the resistor divider R1 is connected
case

not to the load

. This is illustrated in Figure 2. If R1

directly

to the

were connected to the load, the effective resistance be­tween the regulator and the load would be:



RR

R

×

PP





IN

*CONNECT R1 TO CASE
CONNECT R2 TO LOAD

Figure 2. Connections for Best Load Regulation



+

21

, Resistance



R

1



LT1083 OUTINV

ADJ

R Parasitic Line

=

R

P

PARASITIC

LINE RESISTANCE

R1*

R2*

1083/4/5 ADJ F02

R

L

9

LT1083/LT1084/LT1085

U

WUU

APPLICATIONS INFORMATION

Connected as shown, RP is not multiplied by the divider
ratio. RP is 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.

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 rat­ings 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, case­to-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
new regulators provides a separate thermal resistance and
maximum junction temperature for both the

tion

and the
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.

Power Transistor

. Previous regulators, with a

Control Sec-

compound at the case-to-heat sink interface is strongly
recommended. If the case of the device must be electri­cally 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:

VIN (max continuous) = 9V, V
TA = 75°C, θ

θ

CASE-TO-HEAT SINK

thermal compound.

Power dissipation under these conditions is equal to:

PD = (VIN – V

Junction temperature will be equal to:

TJ = TA + PD (θ

For the Control Section:

TJ = 75°C + 24W (1°C/ W + 0.2°C/W + 0.6°C/W) = 118°C
118°C < 125°C = T
Commercial Range)

For the Power Transistor:

TJ = 75°C + 24W (1°C/ W + 0.2°C/W + 1.6°C/W) = 142°C
142°C < 150°C = T
Commercial Range)

HEAT SINK

OUT

= 1°C/W,

= 0.2°C/W for K package with

)(I

HEAT SINK

) = 24W

OUT

+ θ

(Control Section

JMAX

(Power Transistor

JMAX

= 5V, I

OUT

CASE-TO-HEAT SINK

OUT

= 6A,

+ θJC)

Junction-to-case thermal resistance is specified from the
IC junction to the bottom of the case directly below the die.
This is the lowest resistance path for heat flow. Proper
mounting is required to ensure the best possible thermal
flow from this area of the package to the heat sink. Thermal

10

In both cases the junction temperature is below the
maximum rating for the respective sections, ensuring
reliable operation.

U

TYPICAL APPLICATIONS

LT1083/LT1084/LT1085

7.5A Variable Regulator

T1

TRIAD

F-269U

110VAC

1N4003

1% FILM RESISTOR

*

L: DALE TO-5 TYPE
T2: STANCOR 11Z-2003

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

C30B

20Ω

20Ω

C30B

1N4003

82k 15k

10k

1N4148

1µF

3

560Ω

T2

2

1

2

3

7

+

–

–15V

1N4003

8

LT1011

1

4

LT1011

1

1MH

–15V

15V

8

L

OUTIN LT1083 OUTIN

4

–15V

ADJ

1

3

+

2

–

+

C1
50,000µF

15V

200k

4

7

0.1µF

2N3904

3

–

10k

2

+

15K

15V

NC

6

LT1004-1.2

1N914

16k*

11k*

100pF

8

LM301A

7

15V

1µF

16k*

11k*

–15V

750Ω*

2k
OUTPUT
ADJUST

LT1004-1.2

2.7k

1.5k

+

100µF

LT1083/4/5 ADJ TA05

0V TO 35V
OA TO 7.5A

11

LT1083/LT1084/LT1085

R1
121Ω
1%

IN

OUT

ADJ

R2
365Ω
1%

10µF

V

OUT

5V

LT1083

V

IN

1083/4/5 ADJ TA04

+

C1
25µF*

150µF

+

+

*C1 IMPROVES RIPPLE REJECTION.
X

C

SHOULD BE < R1 AT RIPPLE FREQUENCY

U

TYPICAL APPLICATIONS

Paralleling Regulators

IN

LT1083 OUTINV

ADJ

LT1083

IN

ADJ

OUT

R1
120Ω

2 FEET #18 WIRE*

V

OUT

I

0.015Ω

R2

OUT

*THE #18 WIRE ACTS
AS BALLAST RESISTANCE
INSURING CURRENT SHARING
BETWEEN BOTH DEVICES

= 1.25V 1 +

= 0A TO 15A

R2

()

R1

LT1083/4/5 ADJ TA03

Improving Ripple Rejection

12

V

RETURN

IN

Remote Sensing

R

P

LT1083 OUTIN

ADJ

+

10µF

+

25Ω

121Ω

365Ω

(MAX DROP 300mV)

100µF

6

V

1

100pF

IN

7

LM301A

8

2

–

1k

3

+

4

5µF

+

25Ω

V

OUT

5V

R

L

RETURN

1083/4/5 ADJ TA07

U

TYPICAL APPLICATIONS

High Efficiency Regulator with Switching Preregulator

LT1083/LT1084/LT1085

V

28V

MR1122

1M

LT1011

1mH

240Ω

2k

V

OUT

+

10,000µF

470Ω

28V

+

–

1N914

1N914

4N28

10k

10k

LT1083 OUTIN

ADJ

1083/4/5 ADJ TA06

28V

IN

10k

1k

1.2V to 15V Adjustable Regulator

V

IN

+

C1*
10µF

LT1083

IN

ADJ

OUT

R1

90.9Ω

+

R2
1k

V

C2
100µF

OUT

†

*NEEDED IF DEVICE IS FAR FROM FILTER CAPACITORS

†

V

OUT

= 1.25V 1 +

R2

(

)

R1

5V Regulator with Shutdown*

LT1083

ADJ

2N3904

OUT

121Ω
1%

365Ω
1%

V

TTL

IN

IN

+

10µF

1k

1k

*OUTPUT SHUTS DOWN TO 1.3V

1083/4/5 ADJ TA08

+

100µF

1083/4/5 ADJ TA09

V

OUT

5V

13

LT1083/LT1084/LT1085

PACKAGE DESCRIPTION

U

Dimension in inches (millimeters) unless otherwise noted.

K Package

2-Lead TO-3 Metal Can

(LTC DWG # 05-08-1310)

0.320 – 0.350
(8.13 – 8.89)

0.420 – 0.480

(10.67 – 12.19)

0.210 – 0.220
(5.33 – 5.59)

0.425 – 0.435

(10.80 – 11.05)

0.067 – 0.077
(1.70 – 1.96)

0.760 – 0.775

(19.30 – 19.69)

0.038 – 0.043
(0.965 – 1.09)

1.177 – 1.197

(29.90 – 30.40)

0.060 – 0.135

(1.524 – 3.429)

(16.64 – 17.15)

0.490 – 0.510

(12.45 – 12.95)

R

0.655 – 0.675

0.151 – 0.161
(3.86 – 4.09)

DIA, 2PLCS

0.167 – 0.177
(4.24 – 4.49)

R

K2 (TO-3) 1098

0.256

(6.502)

0.060

(1.524)

0.300

(7.620)

BOTTOM VIEW OF DD PAK

HATCHED AREA IS SOLDER PLATED

COPPER HEAT SINK

(1.524)

(1.905)

0.060

0.075

0.183

(4.648)

M Package

3-Lead Plastic DD Pak

(LTC DWG # 05-08-1460)

0.060

(1.524)

TYP

0.330 – 0.370

(8.382 – 9.398)

+0.012

0.143
–0.020

+0.305

3.632

()

–0.508

0.050

(1.270)

BSC

0.390 – 0.415

(9.906 – 10.541)

15

° TYP

0.090 – 0.110

(2.286 – 2.794)

0.165 – 0.180

(4.191 – 4.572)

0.059

(1.499)

TYP

0.013 – 0.023

(0.330 – 0.584)

0.045 – 0.055

(1.143 – 1.397)

+0.008

0.004
–0.004

+0.203

0.102

()

–0.102

0.095 – 0.115

(2.413 – 2.921)

± 0.012

0.050

(1.270 ± 0.305)

M (DD3) 1098

14

PACKAGE DESCRIPTION

0.560

(14.224)

0.325

(8.255)

0.580

(14.732)

0.275

(6.985)

0.700

(17.780)

0.830 – 0.870

(21.08 – 22.10)

LT1083/LT1084/LT1085

U

Dimension in inches (millimeters) unless otherwise noted.

P Package

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

(LTC DWG # 05-08-1450)

0.620 – 0.64O

0.620 – 0.64O

(15.75 – 16.26)

0.580 – 0.6OO

0.580 – 0.6OO

(14.73 – 15.24)

(14.73 – 15.24)

(15.75 – 16.26)

MOUNTING HOLE

0.115 – 0.145
(2.92 – 3.68)

DIA

0.170 – 0.2OO
(4.32 – 5.08)

EJECTOR PIN MARKS

0.105 – 0.125
(2.67 – 3.18)

DIA

18° – 22°

0.187 – 0.207
(4.75 – 5.26)

0.060 – 0.080
(1.52 – 2.03)

BOTTOM VIEW OF TO-3P

HATCHED AREA IS SOLDER PLATED

COPPER HEAT SINK

0.980 – 1.070

(24.892 – 27.178)

0.098

(2.489)

0.124

(3.149)

0.390 – 0.415

(9.906 – 10.541)

0.460 – 0.500

(11.684 – 12.700)

0.780 – 0.800

(19.81 – 20.32)

0.042 – 0.052
(1.07 – 1.32)

0.170
(4.32)

MAX

0.074 – 0.084
(1.88 – 2.13)

T Package

3-Lead Plastic TO-220

(LTC DWG # 05-08-1420)

0.147 – 0.155

(3.734 – 3.937)

0.230 – 0.270

(5.842 – 6.858)

0.330 – 0.370

(8.382 – 9.398)

0.113 – 0.123
(2.87 – 3.12)

DIA

0.570 – 0.620

(14.478 – 15.748)

0.215
(5.46)

BSC

0.165 – 0.180

(4.191 – 4.572)

3° – 7°

0.087 – 0.102
(2.21 – 2.59)

0.020 – 0.040
(0.51 – 1.02)

P3 0996

0.045 – 0.055

(1.143 – 1.397)

0.520 – 0.570

(13.208 – 14.478)

0.100

(2.540)

BSC

0.028 – 0.038

(0.711 – 0.965)

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.

0.218 – 0.252

(5.537 – 6.401)

0.050

(1.270)

TYP

0.013 – 0.023

(0.330 – 0.584)

0.095 – 0.115

(2.413 – 2.921)

T3 (TO-220) 1098

15

LT1083/LT1084/LT1085

U

TYPICAL APPLICATIONS

Automatic Light Control

V

IN

LT1083

IN

+

10µF

OUT

ADJ

Protected High Current Lamp Driver

LT1083

OUT

TTL OR

CMOS

10k

ADJ

1.2k

100µF

1083/4/5 ADJ TA10

12V

5A

IN

15V

1083/4/5 ADJ TA11

RELATED PARTS

PART NUMBER DESCRIPTION COMMENTS

LT1086 1.5A Low Dropout Regulator Fixed 2.85V, 3.3V, 3.6V, 5V and 12V Output
LT1117 800mA Low Dropout Regulator Fixed 2.85V, 3.3V, 5V or Adjustable Output
LT1584/LT1585/LT1587 7A/4.6A/3A Fast Response Low Dropout Regulators For High Performance Microprocessors
LT1580 7A Very Low Dropout Linear Regulator 0.54V Dropout at 7A, Fixed 2.5V
LT1581 10A Very Low Dropout Linear Regulator 0.43V Dropout at 10A, Fixed 2.5V
LT1430 High Power Step-Down Switching Regulator 5V to 3.3V at 10A, >90% Efficiency
LT1575 UltraFastTM Transient Response LDO Controller External MOSFET Pass Element
LT1573 UltraFast Transient Response LDO Controller External PNP Pass Element
UltraFast is a trademark of Linear Technology Corporation.

1083fds, sn1083 LT/TP 0200 2K REV D • PRINTED IN USA

 LINEAR TECHNOLOGY CORPORATION 1994

16

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone] ● FAX: [phone]

●

www.linear-tech.com

and Adjustable

OUT

and Adjustable

OUT