Datasheet LT1085MK-5, LT1085IM-3.6, LT1085CK-12, LT1084MK-5, LT1084CT-5 Datasheet (Linear Technology)

FEATURES

■

Three-Terminal 3.3V, 3.6V, 5V and 12V

■

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

■

Adjustable Versions Available

U

APPLICATIO S

■

High Efficiency Linear Regulators

■

Post Regulators for Switching Supplies

■

Constant Current Regulators

■

Battery Chargers

DEVICE OUTPUT CURRENT*

LT1083 7.5 Amps
LT1084 5.0 Amps
LT1085 3.0 Amps

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

LT1083/LT1084/LT1085 Fixed

3A, 5A, 7.5A Low Dropout

Positive Fixed Regulators

U

DESCRIPTIO

The LT®1083 series of positive adjustable regulators are
designed to provide 3A, 5A and 7.5A 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 output voltage to
1%. Current limit is also trimmed, minimizing the stress
on both the regulator and power source circuitry under
overload conditions.

The LT1083 series devices are pin compatible with older
three-terminal regulators. A 10µF output capacitor is
required on these new devices; however, this is usually
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.

U

TYPICAL APPLICATIO

5V, 7.5A Regulator

VIN ≥ 6.5V 5V AT 7.5A

+

10µF

LT1083-5

*REQUIRED FOR STABILITY

+

22µF*
TANTALUM

LT1083/4/5 TA01

Dropout Voltage vs Output Current

2

1

INPUT/OUTPUT VOLTAGE DIFFERENTIAL (V)

0

0

I

/2

FULLLOAD

OUTPUT CURRENT (A)

I

FULLLOAD

1083/4/5 TA02

1

LT1083/LT1084/LT1085 Fixed

WWWU

ABSOLUTE AXI U RATI GS

(Note 1)

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

Input Voltage* ........................................................ 30V

Operating Input Voltage

3.3V, 3.6V Devices ........................................... 20V

5V Devices ....................................................... 20V

12V Devices ..................................................... 25V

Operating Junction Temperature Range

“C” Grades

Control Section .............................. 0°C to 125°C

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

“M” Grades

Control Section .......................... –55°C to 150°C

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

UU

W

PACKAGE/ORDER I FOR ATIO

V

IN

GND

2-LEAD TO-3 METAL CAN

2

1

K PACKAGE

θJA = 35°C/W

CASE IS
OUTPUT

ORDER PART NUMBER

LT1083CK-5
LT1083CK-12
LT1083MK-5
LT1083MK-12
LT1084CK-5
LT1084CK-12

LT1084MK-5
LT1084MK-12
LT1085CK-5
LT1085CK-12
LT1085MK-5
LT1085MK-12

OBSOLETE NOT RECOMMENDED

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

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

*Although the devices maximum operating voltage is limited, (20V for a
3V, 5V device, and 25V for a 12V device) the devices are guaranteed to
withstand transient input voltages up to 30V. For input voltages greater
than the maximum operating input voltage some degradation of
specifications will occur. For input/output voltage differentials greater than
15V, a minimum external load of 5mA is required to maintain regulation.

U

UU

PRECO DITIO I G

100% Thermal Limit Functional Test.

ORDER PART NUMBER

TAB IS
OUTPUT

FRONT VIEW

3

2

1

P PACKAGE

3-LEAD TO-3P PLASTIC

θJA = 45°C/W

V

V

GND

IN

OUT

LT1083CP-5
LT1083CP-12
LT1084CP-5
LT1084CP-12

FOR NEW DESIGNS

TAB IS
OUTPUT

Consult factory for parts specified with wider operating temperature ranges.

FRONT VIEW

3

2

1

T PACKAGE

3-LEAD PLASTIC TO-220

= 50°C/W

θ

JA

V

IN

V

OUT

GND

LT1084CT-3.3
LT1084CT-5
LT1084CT-12
LT1085CT-3.3
LT1085CT-3.6
LT1085CT-5
LT1085CT-12

2

FRONT VIEW

3

TAB IS

OUTPUT

3-LEAD PLASTIC DD

*WITH PACKAGE SOLDERED TO 0.52IN
COPPER AREA OVER BACKSIDE GROUND
PLANE OR INTERNAL POWER PLANE. θ
VARY FROM 20°C/W TO > 40°C/W DEPENDING
ON MOUNTING TECHNIQUE.

2

1

M PACKAGE

θJA = 30°C/W*

V

V

GND

2

JA

IN

OUT

CAN

LT1085CM-3.3
LT1085CM-3.6
LT1085IM-3.6

LT1083/LT1084/LT1085 Fixed

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

Output Voltage LT1084-3.3 I

LT1085-3.3 VIN = 5V, I

LT1085-3.6 VIN = 5V, I

LT1085-3.6 5V ≤ VIN ≤ 15V, 0 ≤ I

LT1083/4/5-5 I

LT1083/4/5-12 I

Line Regulation LT1084-3.3 I

LT1085-3.3 4.8V ≤ VIN ≤ 15V, I

LT1085-3.6 4.8V ≤ VIN ≤ 15V, I

LT1083/4/5-5 I

LT1083/4/5-12 I

Load Regulation LT1084-3.3 VIN = 5V, 0 ≤ I

LT1085-3.3 VIN = 5V, 0 ≤ I

LT1085-3.6 VIN = 5.25V, 0 ≤ I

LT1083/4/5-5 VIN = 8V, 0 ≤ I

LT1083/4/5-12 VIN = 15V, 0 ≤ I

Dropout Voltage LT1084/5-3.3 ∆V

LT1085-3.6 ∆V
LT1083/4/5-5 ∆V
LT1083/4/5-12 ∆V

Current Limit LT1083-5 VIN = 10V ● 8.0 9.5 A

LT1083-12 VIN = 17V ● 8.0 9.5 A
LT1084-3.3 VIN = 8V ● 5.5 6.5 A
LT1084-5 VIN = 10V ● 5.5 6.5 A
LT1084-12 VIN = 17V ● 5.5 6.5 A
LT1085-3.3/3.6 VIN = 8V ● 3.2 4.0 A
LT1085-5 VIN = 10V ● 3.2 4.0 A
LT1085-12 VIN = 17V ● 3.2 4.0 A

= 0mA, TJ = 25°C, VIN = 8V (K Package Only) 3.270 3.300 3.330 V

OUT

4.8V ≤ VIN ≤ 15V, 0 ≤ I

= 0mA, TJ = 25°C (K Package Only) 3.270 3.300 3.330 V

4.8V ≤ V

5V ≤ V

OUT

≤ 15V, 0 ≤ I

IN

= 0mA, TJ = 25°C (K Package Only) 3.564 3.600 3.636 V

OUT

≤ 15V, 0 ≤ I

IN

5V ≤ VIN ≤ 15V, 0 ≤ I

VIN = 4.75V, I
V

= 4.75V, I

IN

VIN = 4.75V, I

= 0mA, TJ = 25°C, VIN = 8V (K Package Only) 4.950 5.000 5.050 V

OUT

0 ≤ I

≤ I

OUT

= 0mA, TJ = 25°C, VIN = 15V (K Package Only) 11.880 12.000 12.120 V

OUT

0 ≤ I

≤ I

OUT

= 0mA, TJ = 25°C, 4.8V ≤ VIN ≤ 15V 0.5 6 mV

OUT

= 0mA, TJ = 25°C, 6.5V ≤ VIN ≤ 20V (Notes 2, 3) 0.5 10 mV

OUT

= 0mA, TJ = 25°C, 13.5V ≤ VIN ≤ 25V (Notes 2, 3) 1.0 25 mV

OUT

= 33mV, I

OUT

= 36mV, I

OUT

= 50mV, I

OUT

= 120mV, I

OUT

= 3A, TJ ≥ 0°C 3.350 3.672 V

OUT

= 2.5A, TJ ≥ 0°C 3.450 3.672 V

OUT

= 1.5A, TJ > 0°C 3.528 3.672 V

OUT

FULLOAD

FULLOAD

OUT

OUT

OUT

OUT

OUT

OUT
OUT
OUT

≤ I

OUT

≤ I

OUT

≤ I

OUT

FULLOAD

≤ I

OUT

FULLOAD

≤ 2.5A (Notes 3, 4, 9) ● 3.528 3.672 V

OUT

(Notes 3, 4, 9) ● 3.235 3.300 3.365 V

FULLOAD

(Notes 3, 4, 9) ● 3.235 3.300 3.365 V

FULLOAD

(Note 9) ● 3.500 3.672 V
, TJ ≥ 0°C (Notes 3, 4, 9) 3.528 3.672 V

, 6.5V ≤ VIN ≤ 20V (Notes 4, 6, 7, 9) 4.900 5.000 5.100 V

, 13.5V ≤ VIN ≤ 25V (Notes 4, 6, 7, 9) 11.760 12.000 12.240 V

● 1.0 6 mV

= 0mA, TJ= 25°C 0.5 6 mV

OUT

= 0mA, TJ= 25°C 0.5 6 mV

OUT

● 1.0 6 mV

● 1.0 6 mV

● 1.0 10 mV

● 2.0 25 mV

≤ 5A, TJ = 25°C315mV

● 720 mV

≤ 3A, TJ = 25°C315mV

● 720 mV

≤ 3A, TJ = 25°C315mV

● 720 mV

≤ I

FULLLOAD, TJ

≤ I

FULLLOAD, TJ

= I

FULL LOAD

= I

FULL LOAD

= I

FULL LOAD

= I

OUT

= 25°C (Notes 2, 3, 4, 6) 5 20 mV

● 10 35 mV

= 25°C (Notes 2, 3, 4, 6) 12 36 mV

● 24 72 mV

(Notes 5, 6) ● 1.3 1.5 V
(Notes 5, 6) ● 1.3 1.5 V
(Notes 5, 6) ● 1.3 1.5 V

FULL LOAD

(Notes 5, 6) ● 1.3 1.5 V

3

LT1083/LT1084/LT1085 Fixed

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

Quiescient Current LT1084-3.3 VIN = 18V ● 5.0 10.0 mA

LT1085-3.3 VIN = 18V ● 5.0 10.0 mA
LT1085-3.6 VIN = 18V ● 5.0 10.0 mA
LT1083/4/5-5 VIN ≤ 20V ● 5.0 10.0 mA
LT1083/4/5-12 VIN ≤ 25V ● 5.0 10.0 mA

Thermal Regulation LT1083-5/12 TA = 25°C, 30ms pulse 0.002 0.010 %/W

LT1084-3.3/5/12 0.003 0.015 %/W
LT1085-3.3/3.6/5/12 0.004 0.020 %/W

Ripple Rejection f = 120Hz, C

LT1084-3.3 f = 120Hz, C
LT1085-3.3 f = 120Hz, C
LT1085-3.6 f = 120Hz, C
LT1083/4/5-5 VIN = 8V (Note 6) ● 60 68 dB
LT1083/4/5-12 V

Temperature Stability ● 0.5 %
Long Term Stability TA = 125°C, 1000 Hrs. 0.03 1.0 %
RMS Output Noise TA = 25°C,

(% of V
Thermal Resistance Control Circuitry/Power Transistor (See Applications Information)

Junctrion-to-Case LT1083 K Package 0.6/1.6 °C/W

) 10Hz = ≤ f ≤ 10kHz 0.003 %

OUT

LT1084 K Package 0.75/2.3 °C/W

LT1085 K Package 0.9/3.0 °C/W

= 25µF Tantalum, I

OUT

= 15V (Note 6) ● 54 60 dB

IN

P Package 0.5/1.6 °C/W

P Package 0.65/2.3 °C/W
T Package 0.65/2.7 °C/W

T Package 0.7/3.0 °C/W
DD Package 0.7/3.0 °C/W

= I

OUT

FULLLOAD

= 25µF Tantalum, I

OUT

= 25µF Tantalum, VIN = 6.3V, I

OUT

= 25µF Tantalum, VIN = 6.6V, I

OUT

(Note 4)

OUT

= 5A, VIN = 6.3V ● 60 72 dB

= 3A ● 60 72 dB

OUT

= 3A ● 60 72 dB

OUT

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
dissipation (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 range.

Note 4: I

FULL LOAD

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

is defined in the current limit curves. The I

FULLLOAD

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
T

≥ –40°C.

J

Note 7: 1.7V ≤ (V
Note 8: Dropout voltage 1.7V maximum for LT1084 at

–55°C ≤ T
Note 9: Full load current is not available at all input-output voltages.

See Notes 3, 4, 6.

≤ –40°C.

J

FULL LOAD

– V

IN

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

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

OUT

4

LT1083/LT1084/LT1085 Fixed

UW

TYPICAL PERFOR A CE CHARACTERISTICS

LT1083 Dropout Voltage

2

INDICATES GUARANTEED TEST POINT

–40°C ≤ TJ ≤ 150°C

0°C ≤ TJ ≤ 125°C

1

MINIMUM INPUT/OUTPUT DIFFERENTIAL (V)

0

12345678910

0

TJ = 150°C

TJ = 25°C

TJ = –55°C

OUTPUT CURRENT (A)

LT1083/4/5 FIXED G01

LT1084 Dropout Voltage

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 FIXEDG04

LT1083 Short-Circuit Current

12

10

8

6

–55°C

4

SHORT-CIRCUIT CURRENT (A)

2

I

FULL LOAD

GUARANTEED

0

0

510

INPUT/OUTPUT DIFFERENTIAL (V)

25°C

150°C

20 30 35

15 25

LT1083/4/5 FIXED G02

LT1083 Load Regulation

0.10

∆I = 7.5A

0.05

0

–0.05

–0.10

–0.15

OUTPUT VOLTAGE DEVIATION (%)

–0.20

–50

050

–25 25

TEMPERATURE (°C)

75

100

125

LT1083/4/5 FIXED G03

150

LT1084 Short Circuit Current LT1084 Load Regulation

10

9
8
7
6
5
4
3
2

SHORT-CIRCUIT CURRENT (A)

GUARANTEED

1
0

6

5

0

150°C

25°C

–55°C

I

FULL LOAD

20

15

10

5

INPUT/OUTPUT DIFFERENTIAL (V)

25

LT1083/4/5 FIXED G05

35

30

0.10

∆I = 5A

0.05

0

–0.05

–0.10

–0.15

OUTPUT VOLTAGE DEVIATION (%)

–0.20

–50

–25 25

050

TEMPERATURE (°C)

75

100

125

LT1083/4/5 FIXED G06

150

LT1085 Dropout Voltage

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 FIXED G07

LT1085 Short-Circuit Current

6

5

4

3

2

SHORT-CIRCUIT CURRENT (A)

1

4

0

0

25°C
150°C

–55°C

I

FULL LOAD

GUARANTEED

20 30 35

510

INPUT/OUTPUT DIFFERENTIAL (V)

15 25

LT1083/4/5 FIXED G08

LT1085 Load Regulation

0.10

∆I = 3A

0.05

0

–0.05

–0.10

–0.15

OUTPUT VOLTAGE DEVIATION (%)

–0.20

–50

–25 25

050

TEMPERATURE (°C)

75

100

125

LT1083/4/5 FIXED G09

150

5

LT1083/LT1084/LT1085 Fixed

UW

TYPICAL PERFOR A CE CHARACTERISTICS

LT1083/4/5-5 Ripple Rejection
vs CurrentLT1083/4/5-5 Ripple Rejection

80

70

60

50

40

30

RIPPLE REJECTION (dB)

20

10

V

≤ 3V

RIPPLE

(VIN – V

OUT

I

= I

OUT

0

FULLLOAD

10 1k 10k 100k

100

P-P

) ≥ V

DROPOUT

FREQUENCY (Hz)

(VIN – V

V

RIPPLE

≤ 0.5V

OUT

P-P

) ≥ 3V

1083/4/5 FIXED G10

100

90
80
70

fR = 20kHz

60

V

≤ 0.5V

RIPPLE

50
40
30

RIPPLE REJECTION (dB)

20
10

0

0

0.2 0.6

OUTPUT CURRENT (0 TO I

P-P

0.4

fR = 120Hz
V

RIPPLE

FULLLOAD

≤ 3V

0.8

1083/4/5 FIXED G11

P-P

Temperature Stability

2.0

1.0

0

–1.0

OUTPUT VOLTAGE CHANGE (%)

1.0

)

–2.0

–50

–25

0

25

TEMPERATURE (°C)

50

75

100

LT1183/4/5 FIXED G12

125

150

LT1083/4/5-12 Ripple Rejection

80

70

60

50

40

30

RIPPLE REJECTION (dB)

20

10

V

≤ 3V

RIPPLE

(VIN – V

I

= I

OUT

FULLLOAD

0

10 1k 10k 100k

100

) ≥ V

OUT

DROPOUT

FREQUENCY (Hz)

P-P

(VIN – V

V

RIPPLE

≤ 0.5V

OUT

LT1084 Maximum Power
Dissipation*

60

50

40

30

LT1084CT

POWER (W)

20

P-P

) ≥ 3V

1083/4/5 FIXED G13

LT1083/4/5-12 Ripple Rejection
vs Current

100

90
80
70
60
50
40
30

RIPPLE REJECTION (dB)

20
10

0

0

LT1084MK

LT1084CP

fR = 120Hz
V

RIPPLE

fR = 20kHz
V

≤ 0.5V

RIPPLE

0.2 0.6

OUTPUT CURRENT (0 TO I

P-P

0.4

≤ 3V

P-P

1.0

0.8
)

FULLLOAD

1083/4/5 FIXED G14

LT1085 Maximum Power
Dissipation*

50

40

30

20

POWER (W)

LT1083 Maximum Power
Dissipation*

100

90
80
70
60
50
40

POWER (W)

30
20
10

0

50

* AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE

LT1085MK

LT1083MK

LT1083CP

LT1083CK

60 70 80 90 100 110 120 130 140 150

CASE TEMPERATURE (°C)

LT1083/4/5 FIXED G15

LT1085CT

6

10

0

60 70 80 90 100 110 120 130 140 150

50

* AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE

LT1084CK

CASE TEMPERATURE (°C)

LT1083/4/5 FIXED G16

10

LT1085CK

0

60 70 80 90 100 110 120 130 140 150

50

* AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE

CASE TEMPERATURE (°C)

LT1083/4/5 FIXED G17

BLOCK DIAGRA

W

THERMAL

LIMIT

LT1083/LT1084/LT1085 Fixed

V

IN

+

–

V

OUT

WUUU

APPLICATIO S I FOR ATIO

The LT1083 family of three-terminal regulators are easy to
use and have all the protection features that are expected
in high performance voltage regulators. They are short
circuit protected, have safe area protection as well as
thermal shutdown to turn off the regulator should the
temperature exceed about 165°C.

These regulators 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 they require an
output capacitor for stability.

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 aluminum electrolytic or a 22µF solid tantalum on
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 charac-

GND

LT1083/4/5 BD

teristics 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.

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 capacitance 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-to­output voltage increases.That is the equivalent of having
a negitive resistance since increasing voltage causes
current to decrease. Negitive resistance during current
limit is not unique to the LT1083 series and has been
present on all power IC regulators. The value of negative
resistance is a function of how fast the current limit is

7

LT1083/LT1084/LT1085 Fixed

D1

WUUU

APPLICATIO S I FOR ATIO

folded back as input-to-

output voltage increases. This
negative resistance can react with capacitors or inductors
on the input to cause oscillations 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.

Protection Diodes

In normal operation the LT1083 family does not need any
protection diodes, 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 current in normal operation. Only with high
value output capacitors, such as 1000µF to 5000µF and
with the 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 currents large enough to do any damage.

1N4002

(OPTIONAL)

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.

The problem occurs with a heavy output load when the
input voltage is high and the output voltage is low, such as
immediately after a 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

In applications that require improved ripple rejection the
LT1083 series adjustable regulators should be used. With
LT1083 series adjustable regulators the addition of a
bypass capacitor from the adjust pin to ground will reduce
output ripple by the ratio of V

/1.25V. See LT1083

OUT

series adjustable regulator data sheet.

Load Regulation

IN OUT

V

IN

LT1083

ADJ

+

V

C

OUT

150µF

1083/4/5 AI01

OUT

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.

When power is first turned on, as the input voltage rises,
the output follows the input, allowing the regulator to start

8

Because the LT1083 is a three-terminal device, it is not
possible to provide true remote load sensing. Load regu­lation will not be limited by the resistance of the wire
connecting the regulator to the load. The data sheet
specification for the load regulation is measured at the
bottom of the package. Negative side sensing is a true
Kelvin connection, with the ground pin of the device
returned to the negative side of the load.

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,

WUUU

APPLICATIO S I FOR ATIO

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 new regulators provides a separate thermal resis­tance and maximum junction temperature for both the

Control Section

tors, 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.

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
compound at the case-to-heat sink interface is strongly
recommended. If the case of the device must be electroni­cally 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 electronically connected to the ouput.

and the

Power Section

. Previous regula-

LT1083/LT1084/LT1085 Fixed

For example, using a LT1083-5CP (TO-3P, Commercial)
and assuming:

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

θ

CASE-TO-HEAT SINK

HEAT SINK

= 1°C/W,

= 0.2°C/W for P package with

thermal compound.

Power dissipation under these conditions is equal to:

PD = (VIN – V

OUT

) (I

OUT

) = 24W

Junction temperature will be equal to:

TJ = TA + PD (θ

HEAT SINK

+ θ

For the Control Section:

TJ = 75°C + 24W (1°C/W + 0.2°C/W + 0.5°C/W) =
118°C
118°C < 125°C = T

(Control Section Commer-

JMAX

cial 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

(Power Transistor Commer-

JMAX

cial Range)

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

= 5V, I

OUT

CASE-TO-HEAT SINK

OUT

= 6A,

+ θJC)

TYPICAL APPLICATIO S

High Efficiency Regulator

1M

LT1011

MR1122

1mH

10,000µF

+

–

+

28V

4N28

1N914

28V

INPUT

10k

1k

10k

10k

U

470Ω

1N914

28V

Paralleling Regulators

LT1083-5 OUTIN

GND

LT1083/4/5 TA03

OUTPUT

IN

LT1083-5 OUTINV

GND

LT1083-5

IN

OUT

GND

2 FEET #18 WIRE*

V

= 5V

OUT

I

= 0A TO 15A

0.015Ω

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

LT1083/4/5 TA04

OUT

9

LT1083/LT1084/LT1085 Fixed

U

TYPICAL APPLICATIO S

7.5A Regulator

110VAC

T1

TRIAD

F-269U

1N4003

C30B

20Ω

20Ω

C30B

1N4003

82k

10k

1N4148

1% FILM RESISTOR

*

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

REGULATOR WITH SCR PREREGULATOR TO
LOWER POWER DISSIPATION. ABOUT 1.7V
DIFFERENTIAL IS MAINTAINED ACROSS THE
LT1083 INDEPENDENT OF LOAD CURRENT.

34

1µF

15k

T2

1

560Ω

2

7

2

3

8

+

LT1011

–

–15V

4

LT1011

1

1MH

1N4003

–15V

1

15V

8

L

OUTIN

GND

16k*

11k*

LT1083/4/5 TA05

4

–15V

LT1083-12 OUTIN

1

3

+

2

–

+

C1
50,000µF

LT1004-1.2

1N914

NC

16k*

11k*

100pF

8

6

LM301A

7

15V

1µF

15V

4

3

–

+

200k

7

0.1µF

2N3904

10k

2

15k

15V

12V
0A TO 7.5A

+

100µF

PACKAGE DESCRIPTIO

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

0.060

(1.524)

0.075

(1.905)

0.183

(4.648)

10

U

Dimension in inches (millimeters) unless otherwise noted.

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

0.090 – 0.110

(2.286 – 2.794)

° TYP

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

PACKAGE DESCRIPTIO

LT1083/LT1084/LT1085 Fixed

U

Dimension in inches (millimeters) unless otherwise noted.

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)

K Package

2-Lead TO-3 Metal Can

(LTC DWG # 05-08-1310)

0.760 – 0.775

(19.30 – 19.69)

0.038 – 0.043

(0.965 – 1.09)

1.177 – 1.197

(29.90 – 30.40)

0.067 – 0.077
(1.70 – 1.96)

0.490 – 0.510

(12.45 – 12.95)

R

0.060 – 0.135

(1.524 – 3.429)

0.655 – 0.675

(16.64 – 17.15)

0.151 – 0.161
(3.86 – 4.09)

DIA, 2PLCS

0.167 – 0.177
(4.24 – 4.49)

R

K2 (TO-3) 1098

(9.906 – 10.541)

(11.684 – 12.700)

0.980 – 1.070

(24.892 – 27.178)

(13.208 – 14.478)

0.390 – 0.415

0.460 – 0.500

0.520 – 0.570

0.100

(2.540)

BSC

0.028 – 0.038

(0.711 – 0.965)

T Package

3-Lead Plastic TO-220

(LTC DWG # 05-08-1420)

0.147 – 0.155

(3.734 – 3.937)

DIA

0.230 – 0.270

(5.842 – 6.858)

0.570 – 0.620

(14.478 – 15.748)

0.330 – 0.370

(8.382 – 9.398)

0.218 – 0.252

(5.537 – 6.401)

0.050

(1.270)

TYP

0.165 – 0.180

(4.191 – 4.572)

0.013 – 0.023

(0.330 – 0.584)

0.045 – 0.055

(1.143 – 1.397)

0.095 – 0.115

(2.413 – 2.921)

T3 (TO-220) 1098

0.560

(14.224)

0.325

(8.255)

BOTTOM VIEW OF TO-3P

HATCHED AREA IS SOLDER PLATED

COPPER HEAT SINK

0.580

(14.732)

0.124

(3.149)

0.275

(6.985)

0.700

(17.780)

0.098

(2.489)

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)

0.830 – 0.870

(21.08 – 22.10)

0.580 – 0.6OO

0.580 – 0.6OO

(14.73 – 15.24)

(14.73 – 15.24)

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)

(15.75 – 16.26)

0.113 – 0.123
(2.87 – 3.12)

MOUNTING HOLE

0.170 – 0.2OO
(4.32 – 5.08)

EJECTOR PIN MARKS

0.105 – 0.125
(2.67 – 3.18)

0.215
(5.46)

BSC

0.115 – 0.145
(2.92 – 3.68)

DIA

DIA

18° – 22°

3° – 7°

0.187 – 0.207
(4.75 – 5.26)

0.060 – 0.080
(1.52 – 2.03)

0.087 – 0.102
(2.21 – 2.59)

0.020 – 0.040
(0.51 – 1.02)

P3 0996

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.

11

LT1083/LT1084/LT1085 Fixed

U

TYPICAL APPLICATIO S

Adjusting Output Voltage

VIN > 12V

+

10µF

+

10µF*

*OPTIONAL IMPROVES RIPPLE REJECTION

Low Dropout Negative Supply

V

IN

FLOATING INPUT

LT1085-5

10,000µF

1k

LT1083/4/5 TA06

LT1084-12 OUTIN

GND

+

5V to 10V

100µF

++

LT1083/4/5 TA08

100µF

V

OUT

= –12V

VIN > 11.5V

VIN

Regulator with Reference

LT1085-5

+

10µF

5V

LT1029

LT1083/4/5 TA07

OUT

Battery Backed Up Regulated Supply

LT1084-5

+

SELECT
FOR
CHARGE
RATE

6.5V

10µF

+

10µF

50Ω

LT1084-5

+

+

100µF

5.2V LINE

5.0V BATTERY

100µF

LT1083/4/5 TA09

10V

RELATED PARTS

PART NUMBER DESCRIPTION COMMENTS

LT1129 700mA Micropower Low Dropout Regulator 50µA Quiescent Current
LT1175 500mA Negative Low Dropout Micropower Regulator 45µA IQ, 0.26V Dropout Voltage, SOT-223 Package
LT1374 4.5A, 500kHz Step-Down Converter 4.5A, 0.07Ω Internal Switch, SO-8 Package
LT1529 3A Low Dropout Regulator with 50µA I

Q

LT1573 UltraFastTM Transient Response Low Dropout Regulator Drives External PNP
LT1575 UltraFast Transient Response Low Dropout Regulator Drives External N-Channel MOSFET
LT1580 7A, Very Low Dropout Regulator 0.54V Dropout at 7A, Fixed 2.5V
LT1581 10A, Very Low Dropout Regulator 0.63V Dropout at 10A, Fixed 2.5V
LT1584/85/87 7A/4.6A/3A Fast Response LDOs Fast Transient Response for Microprocessor Applications
LT1735 Synchronous Step-Down Converter High Efficiency, OPTI-LOOPTM Compensation
LT1761 Series 100mA, Low Noise, Low Dropout Micropower Regulators in SOT-23 20µA Quiescent Current, 20µV
LT1762 Series 150mA, Low Noise, LDO Micropower Regulators 25µA Quiescent Current, 20µV
LT1763 Series 500mA, Low Noise LDO Micropower Regulators 30µA Quiescent Current, 20µV
LT1764 3A Low Noise Fast Transient Response LDO 40µV
LT1962 300mA, Low Noise LDO Micropower Regulator 20µV
LT1963 1.5A, Low Noise, Fast Transient Response LDO 40µV
UltraFast and OPTI-LOOP are trademarks of Linear Technology Corporation.

Linear Technology Corporation

12

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone] ● FAX: [phone]

●

www.linear-tech.com

500mV Dropout Voltage

Noise, 5-Lead DD Package

RMS

Noise, MSOP Package

RMS

Noise, SOT-223 Package

RMS

1083ffc LT/LCG 1100 2K REV C • PRINTED IN USA

and Adjustable

OUT

and Adjustable

OUT

Noise, SOT-23 Package

RMS

Noise, MSOP Package

RMS

Noise, SO-8 Package

RMS

© LINEAR TECHNOLOGY CORPORATION 1994