1
LT1083/84/85 Fixed
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.
■
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
The LT1083 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 1083 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 quies-
cent current flows into the load, increasing efficiency.
3A, 5A, 7.5A Low Dropout
Positive Fixed Regulators
FEATURES
DESCRIPTION
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TYPICAL APPLICATION
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■
High Efficiency Linear Regulators
■
Post Regulators for Switching Supplies
■
Constant Current Regulators
■
Battery Chargers
APPLICATIONS
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5V, 7.5A Regulator Dropout Voltage vs Output Current
V
IN
≥ 6.5V 5V AT 7.5A
LT1083-5
LT1083/4/5 TA01
22µF*
TANTALUM
+
10µF
+
*REQUIRED FOR STABILITY
OUTPUT CURRENT (A)
0
INPUT/OUTPUT VOLTAGE DIFFERENTIAL (V)
2
1
0
1083/4/5 TA02
I
FULL LOAD
/2
I
FULL LOAD
2
LT1083/84/85 Fixed
Power Dissipation............................... Internally Limited
Input Voltage (Note 1) ............................................. 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
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ABSOLUTE MAXIMUM RATINGS
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100% Thermal Limit Functional Test.
PRECONDITIONING
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Note 1: 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.
PARAMETER CONDITIONS MIN TYP MAX UNITS
Output Voltage LT1084-3.3 I
OUT
= 0mA, T
J
= 25°C, V
IN
= 8V (K Package Only) 3.270 3.300 3.330 V
0 ≤ I
OUT
≤ 5A, 4.8V ≤ V
IN
≤ 15V (Note 8) ●3.235 3.300 3.365 V
LT1085-3.3 V
IN
= 5V, I
OUT
= 0mA, T
J
= 25°C (K Package Only) 3.270 3.300 3.330 V
4.8V ≤ V
IN
≤ 15V, 0 ≤ I
OUT
≤ 3A (Note 8) ●3.235 3.300 3.365 V
LT1085-3.6 V
IN
= 5V, I
OUT
= 0mA, T
J
= 25°C (K Package Only) 3.564 3.600 3.636 V
5V ≤ V
IN
≤ 15V, 0 ≤ I
OUT
≤ 3A (Note 8) ●3.500 3.672 V
5V ≤ V
IN
≤ 15V, 0 ≤ I
OUT
≤ 3A, TJ ≥ 0°C (Note 8) 3.528 3.672 V
ELECTRICAL CHARACTERISTICS
PACKAGE/ORDER INFORMATION
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ORDER PART NUMBER ORDER PART NUMBER
LT1083CP-5
LT1083CP-12
LT1084CP-5
LT1084CP-12
LT1083CK-5
LT1083CK-12
LT1083MK-5
LT1083MK-12
LT1084CK-5
LT1084CK-12
LT1084MK-5
LT1084MK-12
LT1085CK-5
LT1085CK-12
LT1085MK-5
LT1085MK-12
θ
JA
= 35°C/W θ
JA
= 45°C/W
θ
JA
= 50°C/W
1
2
V
IN
CASE IS
OUTPUT
GND
K PACKAGE
2-LEAD TO-3 METAL CAN
T PACKAGE
3-LEAD PLASTIC TO-220
FRONT VIEW
TAB IS
OUTPUT
3
2
1
VIN
VOUT
GND
V
IN
V
OUT
GND
P PACKAGE
3-LEAD TO-3P PLASTIC
FRONT VIEW
TAB IS
OUTPUT
3
2
1
LT1084CT-3.3
LT1084CT-5
LT1084CT-12
LT1085CT-3.3
LT1085CT-3.6
LT1085CT-5
LT1085CT-12
LT1085CM-3.3
LT1085CM-3.6
V
IN
V
OUT
GND
M PACKAGE
3-LEAD PLASTIC DD
FRONT VIEW
TAB IS
OUTPUT
3
2
1
θ
JA
= 30°C/W*
*WITH PACKAGE SOLDERED TO 0.52IN
2
COPPER AREA OVER BACKSIDE GROUND
PLANE OR INTERNAL POWER PLANE. θ
JA
CAN
VARY FROM 20°C/W TO > 40°C/W DEPENDING
ON MOUNTING TECHNIQUE.
Consult factory for Industrial grade parts.
3
LT1083/84/85 Fixed
PARAMETER CONDITIONS MIN TYP MAX UNITS
Output Voltage LT1085-3.6 5V ≤ V
IN
≤ 15V, 0 ≤ I
OUT
≤ 2.5A (Note 8) ●3.528 3.672 V
V
IN
= 4.75V, I
OUT
= 3A, T
J
≥ 0°C 3.350 3.672 V
V
IN
= 4.75V, I
OUT
= 2.5A, T
J
≥ 0°C 3.450 3.672 V
V
IN
= 4.75V, I
OUT
= 1.5A, T
J
> 0°C 3.528 3.672 V
LT1083/4/5-5 I
OUT
= 0mA, T
J
= 25°C, V
IN
= 8V (K Package Only) 4.950 5.000 5.050 V
0 ≤ I
OUT
≤ I
FULLOAD
, 6.5V ≤ V
IN
≤ 20V (Notes 3, 5, 6, 8) 4.900 5.000 5.100 V
LT1083/4/5-12 I
OUT
= 0mA, T
J
= 25°C, V
IN
= 15V (K Package Only) 11.880 12.000 12.120 V
0 ≤ I
OUT
≤ I
FULLOAD
, 13.5V ≤ V
IN
≤ 25V (Notes 3, 5, 6, 8) 11.760 12.000 12.240 V
Line Regulation LT1084-3.3 I
OUT
= 0mA, T
J
= 25°C, 4.8V ≤ V
IN
≤ 15V 0.5 6 mV
●1.0 6 mV
LT1085-3.3 4.8V ≤ V
IN
≤ 15V, I
OUT
= 0mA, T
J
= 25°C 0.5 6 mV
●1.0 6 mV
LT1085-3.6 4.8V ≤ V
IN
≤ 15V, I
OUT
= 0mA, T
J
= 25°C 0.5 6 mV
●1.0 6 mV
LT1083/4/5-5 I
OUT
= 0mA, T
J
= 25°C, 6.5V ≤ V
IN
≤ 20V (Notes 1, 2) 0.5 10 mV
●1.0 10 mV
LT1083/4/5-12 I
OUT
= 0mA, T
J
= 25°C, 13.5V ≤ V
IN
≤ 25V (Notes 1, 2) 1.0 25 mV
●2.0 25 mV
Load Regulation LT1084-3.3 V
IN
= 5V, 0 ≤ I
OUT
≤ 5A, T
J
= 25°C 3 15 mV
●720 mV
LT1085-3.3 V
IN
= 5V, 0 ≤ I
OUT
≤ 3A, T
J
= 25°C 3 15 mV
●720 mV
LT1085-3.6 V
IN
= 5.25V, 0 ≤ I
OUT
≤ 3A, T
J
= 25°C 3 15 mV
●720 mV
LT1083/4/5-5 V
IN
= 8V, 0 ≤ I
OUT
≤ I
FULLLOAD,
T
J
= 25°C (Notes 1, 2, 3, 5) 5 20 mV
●10 35 mV
LT1083/4/5-12 V
IN
= 15V, 0 ≤ I
OUT
≤ I
FULLLOAD,
T
J
= 25°C (Notes 1, 2, 3, 5) 12 36 mV
●24 72 mV
Dropout Voltage LT1084/5-3.3 ∆V
OUT
= 33mV, I
OUT
= I
FULL LOAD
(Notes 4, 5) ●1.3 1.5 V
LT1085-3.6 ∆V
OUT
= 36mV, I
OUT
= I
FULL LOAD
(Notes 4, 5) ●1.3 1.5 V
LT1083/4/5-5 ∆V
OUT
= 50mV, I
OUT
= I
FULL LOAD
(Notes 4, 5) ●1.3 1.5 V
LT1083/4/5-12 ∆V
OUT
= 120mV, I
OUT
= I
FULL LOAD
(Notes 4, 5) ●1.3 1.5 V
Current Limit LT1083-5 V
IN
= 10V ●8.0 9.5 A
LT1083-12 V
IN
= 17V ●8.0 9.5 A
LT1084-3.3 V
IN
= 8V ●5.5 6.5 A
LT1084-5 V
IN
= 10V ●5.5 6.5 A
LT1084-12 V
IN
= 17V ●5.5 6.5 A
LT1085-3.3/3.6 V
IN
= 8V ●3.2 4.0 A
LT1085-5 V
IN
= 10V ●3.2 4.0 A
LT1085-12 V
IN
= 17V ●3.2 4.0 A
Quiescient Current LT1084-3.3 V
IN
= 18V ●5.0 10.0 mA
LT1085-3.3 V
IN
= 18V ●5.0 10.0 mA
LT1085-3.6 V
IN
= 18V ●5.0 10.0 mA
LT1083/4/5-5 V
IN
≤ 20V ●5.0 10.0 mA
LT1083/4/5-12 V
IN
≤ 25V ●5.0 10.0 mA
Thermal Regulation LT1083-5/12 T
A
= 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
OUT
= 25µF Tantalum, I
OUT
= I
FULLLOAD
LT1084-3.3 f = 120Hz, C
OUT
= 25µF Tantalum, I
OUT
= 5A, V
IN
= 6.3V ●60 72 dB
ELECTRICAL CHARACTERISTICS
4
LT1083/84/85 Fixed
PARAMETER CONDITIONS MIN TYP MAX UNITS
Ripple Rejection LT1085-3.3 f = 120Hz, C
OUT
= 25µF Tantalum, V
IN
= 6.3V, I
OUT
= 3A ●60 72 dB
LT1085-3.6 f = 120Hz, C
OUT
= 25µF Tantalum, V
IN
= 6.6V, I
OUT
= 3A ●60 72 dB
LT1083/4/5-5 V
IN
= 8V (Note 5) ●60 68 dB
LT1083/4/5-12 V
IN
= 15V (Note 5) ●54 60 dB
Temperature Stability ●0.5 %
Long Term Stability T
A
= 125°C, 1000 Hrs. 0.03 1.0 %
RMS Output Noise T
A
= 25°C,
(% of V
OUT
) 10Hz = ≤ f ≤ 10kHz 0.003 %
Thermal Resistance Control Circuitry/Power Transistor (See Applications Information)
Junctrion-to-Case LT1083 K Package 0.6/1.6 °C/W
P Package 0.5/1.6 °C/W
LT1084 K Package 0.75/2.3 °C/W
P Package 0.65/2.3 °C/W
T Package 0.65/2.7 °C/W
LT1085 K Package 0.9/3.0 °C/W
T Package 0.7/3.0 °C/W
DD Package 0.7/3.0 °C/W
ELECTRICAL CHARACTERISTICS
TYPICAL PERFORMANCE CHARACTERISTICS
UW
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 4: 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 5: For LT1083 I
FULL LOAD
is 5A for –55°C ≤ T
J
≤ –40°C and 7.5A for
T
J
≥ –40°C.
Note 6: 1.7V ≤ (V
IN
– V
OUT
) ≤ 25V for LT1084 at –55°C ≤ T
J
≤ –40°C.
Note 7: Dropout voltage 1.7V maximum for LT1084 at –55 ≤ T
J
≤ –40°C.
Note 8: Full load current is not available at all input-output voltages.
See Notes 2,3,5.
OUTPUT CURRENT (A)
0
MINIMUM INPUT/OUTPUT DIFFERENTIAL (V)
1
2
LT1083/4/5 FIXED G01
012345678910
INDICATES GUARANTEED TEST POINT
–40°C ≤ T
J
≤ 150°C
0°C ≤ T
J
≤ 125°C
T
J
= 150°C
T
J
= 25°C
T
J
= –55°C
INPUT/OUTPUT DIFFERENTIAL (V)
0
SHORT-CIRCUIT CURRENT (A)
8
10
12
15 25
LT1083/4/5 FIXED G02
6
4
510 20 30 35
2
0
25°C
–55°C
IFULL LOAD
GUARANTEED
150°C
TEMPERATURE (°C)
–50
–0.20
OUTPUT VOLTAGE DEVIATION (%)
–0.15
–0.10
–0.05
0
050
100 150
LT1083/4/5 FIXED G03
0.05
0.10
–25 25 75 125
∆I = 7.5A
LT1083 Dropout Voltage LT1083 Load Regulation
LT1083 Short-Circuit Current
The ● denotes the specifications which apply over the full operating
temperature range.
Note 1: 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 2: 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 3: 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
5
LT1083/84/85 Fixed
TYPICAL PERFORMANCE CHARACTERISTICS
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LT1084 Dropout Voltage LT1084 Short Circuit Current LT1084 Load Regulation
OUTPUT CURRENT (A)
0
0
MINIMUN INPUT/OUTPUT DIFFERENTIAL (V)
1
1234
LT1083/4/5 FIXEDG04
5
2
6
INDICATES GUARANTEED TEST POINT
–55°C ≤ T
J
≤ 150°C
0°C ≤ T
J
≤ 125°C
T
J
= 150°C
T
J
= –55°C
T
J
= 25°C
INPUT/OUTPUT DIFFERENTIAL (V)
0
0
SHORT-CIRCUIT CURRENT (A)
1
3
4
5
10
7
10 20 25
LT1083/4/5 FIXED G05
2
8
9
6
515 30 35
25°C
–55°C
I
FULL LOAD
GUARANTEED
150°C
TEMPERATURE (°C)
–50
–0.20
–0.15
–0.10
–0.05
0.05
0.10
OUTPUT VOLTAGE DEVIATION (%)
0
050
100 150
LT1083/4/5 FIXED G06
–25 25 75 125
∆I = 5A
LT1085 Dropout Voltage
OUTPUT CURRENT (A)
0
0
MINIMUM INPUT/OUTPUT DIFFERENTIAL (V)
1
2
12
LT1083/4/5 FIXED G07
34
INDICATES GUARANTEED TEST POINT
T
J
= 150°C T
J
= 25°C
–55°C ≤ T
J
≤ 150°C
T
J
= –55°C
0°C ≤ T
J
≤ 125°C
TEMPERATURE (°C)
–50
–0.20
–0.15
–0.10
–0.05
0.05
0.10
OUTPUT VOLTAGE DEVIATION (%)
0
050
100 150
LT1083/4/5 FIXED G09
–25 25 75 125
∆I = 3A
LT1085 Load Regulation
INPUT/OUTPUT DIFFERENTIAL (V)
0
SHORT-CIRCUIT CURRENT (A)
4
5
6
15 25
LT1083/4/5 FIXED G08
3
2
510 20 30 35
1
0
25°C
150°C
I
FULL LOAD
GUARANTEED
–55°C
LT1085 Short-Circuit Current
LT1083/4/5-5 Ripple Rejection
vs Current
LT1083/4/5-5 Ripple Rejection
OUTPUT CURRENT (0 TO I
FULL LOAD
)
0
RIPPLE REJECTION (dB)
100
90
80
70
60
50
40
30
20
10
00.4 0.8 1.0
1083/4/5 FIXED G11
0.2 0.6
f
R
= 120Hz
V
RIPPLE
≤ 3V
P-P
f
R
= 20kHz
V
RIPPLE
≤ 0.5V
P-P
TEMPERATURE (°C)
–50
OUTPUT VOLTAGE CHANGE (%)
0
1.0
150
LT1183/4/5 FIXED G12
–1.0
–2.0 050 100
2.0
–25 25 75 125
Temperature Stability
30
40
50
20
10
0
60
70
80
FREQUENCY (Hz)
RIPPLE REJECTION (dB)
10 1k 10k 100k
1083/4/5 FIXED G10
100
V
RIPPLE
≤ 0.5V
P-P
V
RIPPLE
≤ 3V
P-P
(V
IN
– V
OUT
) ≥ 3V
(V
IN
– V
OUT
) ≥ V
DROPOUT
I
OUT
= I
FULL LOAD
6
LT1083/84/85 Fixed
TYPICAL PERFORMANCE CHARACTERISTICS
UW
30
40
50
20
10
0
60
70
80
FREQUENCY (Hz)
RIPPLE REJECTION (dB)
10 1k 10k 100k
1083/4/5 FIXED G13
100
V
RIPPLE
≤ 0.5V
P-P
V
RIPPLE
≤ 3V
P-P
(V
IN
– V
OUT
) ≥ 3V
(V
IN
– V
OUT
) ≥ V
DROPOUT
I
OUT
= I
FULL LOAD
LT1083/4/5-12 Ripple Rejection
CASE TEMPERATURE (°C)
50
POWER (W)
100
90
80
70
60
50
40
30
20
10
0
LT1083/4/5 FIXED G15
60 70 80 90 100 110 120 130 140 150
LT1083MK
LT1083CP
LT1083CK
* AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE
LT1083 Maximum Power
Dissipation*
OUTPUT CURRENT (0 TO I
FULL LOAD
)
0
RIPPLE REJECTION (dB)
100
90
80
70
60
50
40
30
20
10
00.4 0.8 1.0
1083/4/5 FIXED G14
0.2 0.6
f
R
= 120Hz
V
RIPPLE
≤ 3V
P-P
f
R
= 20kHz
V
RIPPLE
≤ 0.5V
P-P
LT1083/4/5-12 Ripple Rejection
vs Current
LT1085 Maximum Power
Dissipation*
CASE TEMPERATURE (°C)
50
POWER (W)
50
40
30
20
10
0
LT1083/4/5 FIXED G17
60 70 80 90 100 110 120 130 140 150
LT1085MK
LT1085CT
LT1085CK
* AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE
LT1084 Maximum Power
Dissipation*
CASE TEMPERATURE (°C)
50
POWER (W)
60
50
40
30
20
10
0
LT1083/4/5 FIXED G16
60 70 80 90 100 110 120 130 140 150
LT1084MK
LT1084CT LT1084CP
* AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE
LT1084CK
7
LT1083/84/85 Fixed
BLOCK DIAGRAM
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APPLICATIONS INFORMATION
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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 stabil-
ity 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-
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.
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 capaci-
tance 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 mono-
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 negitive resis-
tance 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 folded back as input-to-
THERMAL
LIMIT 
GND
LT1083/4/5 BD
V
IN
–
+
8
LT1083/84/85 Fixed
APPLICATIONS INFORMATION
WUU U
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 operat-
ing 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
OUT
/1.25V. See LT1083
series adjustable regulator data sheet.
Load Regulation
Because the LT1083 is a three-terminal device, it is not
possible to provide true remote load sensing. Load regu-
lation 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 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
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 neces-
sarily easy to solve; however it does not cause any prob-
lems 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 sup-
ply cycling or even plugging and unplugging in the system
will not generate currents large enough to do any damage.
V
IN
V
OUT
LT1083
ADJ
IN OUT
LT1083/4/5 AI01
C
OUT
150µF
+
D1
1N4002
(OPTIONAL)
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
up into very heavy loads. During the start-up, as the input
9
LT1083/84/85 Fixed
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 Sec-
tion
and the
Power Section
. 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.
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 electroni-
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 electronically connected to the ouput.
For example, using a LT1083-5CK (TO-3, Commercial)
and assuming:
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 Commer-
cial 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 Commer-
cial Range)
In both cases the junction temperature is below the
maximum rating for the respective sections, ensuring
reliable operation.
APPLICATIONS INFORMATION
WUU U
High Efficiency Regulator
+
–
+
28V
INPUT
28V
470Ω
28V
4N28
1N914
1N914
LT1011
10k
10k
10k
1k 1M
MR1122
1mH
10,000µF
OUTPUT
LT1083-5 OUTIN
GND
LT1083/4/5 TA03
TYPICAL APPLICATIONS
U
10
LT1083/84/85 Fixed
TYPICAL APPLICATIONS
U
Paralleling Regulators
7.5A Regulator
15V
15V
15V
110VAC
T1
TRIAD
F-269U
–
+
–
+
+ +
–
+
OUTIN
GND
LT1083-12 OUTIN
GND
C30B
C30B
34
20Ω
20Ω
12
L
1MH
T2
1N4003
1N4148
1N4003
1N914
C1
50,000µF 100µF
LT1004-1.2
1N4003
1µF
0.1µF
1µF
100pF
560Ω16k* 16k*
11k*
11k*
12V
0A TO 7.5A
10k
82k 15k
2
2
2
3
3
3
8
8
–15V
–15V
–15V
15V
4
4
4
7
7
1
1
200k
15k
10k
2N3904
NC
8
6
7
1
LT1011
LT1011
LM301A
*
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.
LT1083/4/5 TA05
LT1083-5 OUTINV
IN
V
OUT
= 5V
I
OUT
= 0A TO 15A
GND
LT1083-5
0.015Ω
OUT
2 FEET #18 WIRE*
IN
GND
*THE #18 WIRE ACTS
AS BALLAST RESISTANCE
INSURING CURRENT SHARING
BETWEEN BOTH DEVICES
LT1083/4/5 TA04
11
LT1083/84/85 Fixed
TYPICAL APPLICATIONS
U
+
+
V
IN
50Ω
LT1084-5
LT1083/4/5 TA09
5.2V LINE
5.0V BATTERY
+
LT1084-5
SELECT
FOR
CHARGE
RATE
6.5V
100µF
10µF
10µF
Adjusting Output Voltage
+
+
V
IN
> 11.5V
5V
OUT
LT1085-5
LT1029
LT1083/4/5 TA07
10V
10µF 100µF
Regulator with Reference
+
V
IN
V
OUT
= –12V
LT1083/4/5 TA08
10,000µF
FLOATING INPUT
100µF
+
LT1084-12 OUTIN
GND
Low Dropout Negative Supply
Battery Backed Up Regulated Supply
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
+
+
+
VIN > 12V LT1085-5
LT1083/4/5 TA06
5V to 10V
10µF
*OPTIONAL IMPROVES RIPPLE REJECTION
10µF* 1k
100µF
12
LT1083/84/85 Fixed
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900
●
FAX
: (408) 434-0507
●
TELEX
: 499-3977
0.580 – 0.6OO
(14.73 – 15.24)
0.830 – 0.870
(21.08 – 22.10)
0.170 
(4.32)
MAX
0.780 – 0.800
(19.81 – 20.32)
0.620 – 0.64O
(15.75 – 16.26)
0.170 – 0.2OO
(4.32 – 5.08)
MOUNTING HOLE
0.115 – 0.145
(2.92 – 3.68)
DIA
0.580 – 0.6OO
(14.73 – 15.24)
0.830 – 0.870
(21.08 – 22.10)
0.780 – 0.800
(19.81 – 20.32)
0.620 – 0.64O
(15.75 – 16.26)
0.215 
(5.46)
BSC
0.113 – 0.123
(2.87 – 3.12)
0.042 – 0.052
(1.07 – 1.32)
0.074 – 0.084
(1.88 – 2.13)
0.187 – 0.207
(4.75 – 5.26)
0.060 – 0.080
(1.52 – 2.03)
18° – 22°
3° – 7°
0.087 – 0.102
(2.21 – 2.59)
0.020 – 0.040
(0.51 – 1.02)
EJECTOR PIN MARKS
0.105 – 0.125
(2.67 – 3.18)
DIA
P3 0892
K2 0592
0.038 – 0.043
(0.965 – 1.09)
0.060 – 0.135
(1.524 – 3.429)
0.320 – 0.350
(8.13 – 8.89)
0.420 – 0.480
(10.67 – 12.19)
0.760 – 0.775
(19.30 – 19.69)
0.495 – 0.525
(12.57 – 13.34)
0.167 – 0.177
(4.24 – 4.49)
R TYP
0.152 – 0.161
(3.86 – 4.09)
DIA
1.177 – 1.197
(29.90 – 30.40)
0.655 – 0.675
(16.64 – 17.15)
0.067 – 0.077
(1.70 – 1.96)
0.210 – 0.220
(5.33 – 5.59)
0.425 – 0.435
(10.80 – 11.05)
K Package
2-Lead TO-3 Metal Can P Package
3-Lead TO-3P Plastic
PACKAGE DESCRIPTION
U
Dimension in inches (millimeters) unless otherwise noted.
0.139 – 0.153
(3.531 – 3.886)
DIA
0.380 – 0.420
(9.652 – 10.668)
0.090 – 0.110
(2.286 – 2.794)
0.235 – 0.270
(5.969 – 6.858)
0.027 – 0.037
(0.686 – 0.940)
0.079 – 0.135
(2.007 – 3.429)
T3 0693
0.035 – 0.055
(0.889 – 1.397)
0.169 – 0.185
(4.293 – 4.699)
0.079 – 0.115
(2.007 – 2.921)
0.015 – 0.025
(0.381 – 0.635)
1.005 – 1.080
(25.527 – 27.432)
0.560 – 0.650
(14.224 – 16.510)
0.150
3.810
MIN
0.050
(1.270)
TYP
DD3 0693
0.022 ± 0.005
(0.559 ± 0.127)
0.105 ± 0.008
(2.667 ± 0.203)
0.004+0.008
–0.004
()
0.102+0.203
–0.102
0.050 ± 0.012
(1.270 ± 0.305)
0.059
(1.499)
TYP
0.050 ± 0.008
(1.270 ± 0.203)
0.175 ± 0.008
(4.445 ± 0.203)
0.060
(1.524)
0.401 ± 0.015
(10.185 ± 0.381)
15° TYP
0.050 ± 0.008
(1.270 ± 0.203)
0.331+0.012
–0.020
()
8.407+0.305
–0.508
0.143+0.012
–0.020
()
3.632+0.305
–0.508
0.100 ± 0.010
(2.5402 ± 0.254)
T Package
3-Lead Plastic TO-220
M Package
3-Lead Plastic DD
© LINEAR TECHNOLOGY CORPORATION 1994
LT/GP 06/94 5K REV B • PRINTED IN USA