1
LT1083/LT1084/LT1085
■
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
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 differen-
tial 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 quies-
cent current flows into the load, increasing efficiency.
7.5A, 5A, 3A Low Dropout
Positive Adjustable Regulators
121Ω
1%
IN OUT
ADJ
365Ω
1%
10µF
5V AT 7.5A
LT1083
V
IN
≥ 6.5V
1083/4/5 ADJ TA01
+
10µF*
TANTALUM
+
*REQUIRED FOR STABILITY
5V, 7.5A Regulator
DEVICE OUTPUT CURRENT*
LT1083 7.5A
LT1084 5.0A
LT1085 3.0A
*For a 1.5A low dropout regulator see the LT1086 data sheet.
■
High Efficiency Linear Regulators
■
Post Regulators for Switching Supplies
■
Constant Current Regulators
■
Battery Chargers
OUTPUT CURRENT
0
INPUT/OUTPUT VOLTAGE DIFFERENTIAL (V)
2
1
0
1083/4/5 ADJ TA02
IFULL LOAD
Dropout Voltage vs Output Current
APPLICATIO S
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FEATURES
TYPICAL APPLICATIO
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DESCRIPTIO
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, LTC and LT are registered trademarks of Linear Technology Corporation.
2
LT1083/LT1084/LT1085
PARAMETER CONDITIONS MIN TYP MAX UNITS
Reference Voltage I
OUT
= 10mA, T
J
= 25°C,
(V
IN
– V
OUT
) = 3V 1.238 1.250 1.262 V
10mA ≤ I
OUT
≤ I
FULL LOAD
1.5V ≤ (V
IN
–
V
OUT
) ≤ 25V (Notes 4, 6, 7) ●1.225 1.250 1.270 V
Line Regulation I
LOAD
= 10mA, 1.5V ≤ (V
IN
– V
OUT
) ≤ 15V, T
J
= 25°C (Notes 2, 3) 0.015 0.2 %
●0.035 0.2 %
M Grade: 15V ≤ (V
IN
–
V
OUT
) ≤ 35V (Notes 2, 3) ●0.05 0.5 %
C, I Grades: 15V ≤ (V
IN
–
V
OUT
) ≤ 30V (Notes 2, 3) ●0.05 0.5 %
ABSOLUTE MAXIMUM RATINGS
W
WW
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ELECTRICAL CHARACTERISTICS
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
“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
100% thermal shutdown functional test.
PACKAGE/ORDER INFORMATION
W
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ORDER PART
NUMBER ORDER PART
NUMBER
LT1083CP
LT1084CP
LT1084CT
LT1084IT
LT1085CT
LT1085IT
T PACKAGE
3-LEAD PLASTIC TO-220
FRONT VIEW
TAB
IS
OUTPUT
3
2
1
V
IN
V
OUT
ADJ
V
IN
V
OUT
ADJ
P PACKAGE
3-LEAD PLASTIC TO-3P
FRONT VIEW
TAB IS
OUTPUT
3
2
1
1
2
V
IN
CASE IS
OUTPUT
BOTTOM VIEW
ADJ
K PACKAGE
2-LEAD TO-3 METAL CAN
θ
JA
= 35°C/W
θ
JA
= 35°C/W
θ
JA
= 50°C/W
VIN
VOUT
ADJ
3
2
1
M PACKAGE
3-LEAD PLASTIC DD
FRONT VIEW
TAB
IS
OUTPUT
3
2
1
*WITH PACKAGE SOLDERED TO 0.5IN
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.
θ
JA
= 30°C/W*
LT1083CK
LT1083MK
LT1084CK
LT1084MK
LT1085CK
LT1085MK
LT1085CM
PRECO DITIO I G
UUU
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
(Note 1)
3
LT1083/LT1084/LT1085
PARAMETER CONDITIONS MIN TYP MAX UNITS
Load Regulation (V
IN
– V
OUT
) = 3V
10mA ≤ I
OUT
≤ I
FULL LOAD
T
J
= 25°C (Notes 2, 3, 4, 6) 0.1 0.3 %
●0.2 0.4 %
Dropout Voltage ∆V
REF
= 1%, I
OUT
= I
FULLLOAD
(Notes 5, 6, 8) ●1.3 1.5 V
Current Limit
LT1083 (V
IN
– V
OUT
) = 5V ●8.0 9.5 A
(V
IN
– V
OUT
) = 25V ●0.4 1.0 A
LT1084 (V
IN
– V
OUT
) = 5V ●5.5 6.5 A
(V
IN
– V
OUT
) = 25V ●0.3 0.6 A
LT1085 (V
IN
– V
OUT
) = 5V ●3.2 4.0 A
(V
IN
– V
OUT
) = 25V ●0.2 0.5 A
Minimum Load Current (V
IN
– V
OUT
) = 25V ●510 mA
Thermal Regulation T
A
= 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
ADJ
= 25µF, C
OUT
= 25µF Tantalum
I
OUT
= I
FULL LOAD
, (V
IN
– V
OUT
) = 3V (Notes 6, 7, 8) ●60 75 dB
Adjust Pin Current T
J
= 25°C55µA
●120 µA
Adjust Pin Current Change 10mA ≤ I
OUT
≤ I
FULL LOAD
1.5V ≤ (V
IN
– V
OUT
) ≤ 25V (Note 6) ●0.2 5 µA
Temperature Stability ●0.5 %
Long Term Stability T
A
= 125°C, 1000 Hrs 0.3 1 %
RMS Output Noise (% of V
OUT
)T
A
= 25°C
10Hz = ≤ f ≤ 10kHz 0.003 %
Thermal Resistance Junction-to-Case Control Circuitry/Power Transistor
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
M, T Packages 0.7/3.0 °C/W
ELECTRICAL CHARACTERISTICS
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
FULL LOAD
is 5A for –55°C ≤ T
J
< – 40°C and 7.5A for
T
J
≥ –40°C.
Note 7: 1.7V ≤ (V
IN
– V
OUT
) ≤ 25V for LT1084 at –55°C ≤ T
J
≤ –40°C.
Note 8: Dropout is 1.7V maximum for LT1084 at –55°C ≤ T
J
≤ –40°C.
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
4
LT1083/LT1084/LT1085
TYPICAL PERFORMANCE CHARACTERISTICS
UW
OUTPUT CURRENT (A)
0
MINIMUM INPUT/OUTPUT DIFFERENTIAL (V)
1
2
LT1083/4/5 ADJ 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 ADJ G02
6
4
510 20 30 35
2
0
25°C
150°C
I
FULL LOAD
GUARANTEED
–55°C
TEMPERATURE (°C)
–50
–0.20
OUTPUT VOLTAGE DEVIATION (%)
–0.15
–0.10
–0.05
0
050
100 150
LT1083/4/5 ADJ G03
0.05
0.10
–25 25 75 125
∆I = 7.5A
OUTPUT CURRENT (A)
0
0
MINIMUN INPUT/OUTPUT DIFFERENTIAL (V)
1
1234
LT1083/4/5 ADJ G04
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 ADJ G05
2
8
9
6
515 30 35
25°C
–55°C
150°C
GUARANTEED
I
FULL LOAD
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 ADJ G06
–25 25 75 125
∆I = 5A
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 ADJ G09
–25 25 75 125
∆I = 3A
INPUT/OUTPUT DIFFERENTIAL (V)
0
SHORT-CIRCUIT CURRENT (A)
4
5
6
15 25
LT1083/4/5 ADJ G08
3
2
510 20 30 35
1
0
25°C
–55°C
I
FULL LOAD
GUARANTEED
150°C
OUTPUT CURRENT (A)
0
0
MINIMUM INPUT/OUTPUT DIFFERENTIAL (V)
1
2
12
LT1083/4/5 ADJ 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
LT1085 LT1085 LT1085
Dropout Voltage Short-Circut Current Load Regulation
LT1084 LT1084 LT1084
Dropout Voltage Short-Circut Current Load Regulation
LT1083 LT1083 LT1083
Dropout Voltage Short-Circut Current Load Regulation
5
LT1083/LT1084/LT1085
TYPICAL PERFORMANCE CHARACTERISTICS
UW
Minimum Operating Current Temperature Stability Adjust Pin Current
INPUT/OUTPUT DIFFERENTIAL (V)
0
0
MINIMUM OPERATING CURRENT (mA)
1
3
4
5
10
7
10 20 25
LT1083/4/5 ADJ G10
2
8
9
6
515 30 35
T
J
= –55°C
T
J
= 150°C
T
J
= 25°C
TEMPERATURE (°C)
–50
1.27
1.26
1.25
1.24
1.23
REFERENCE VOLTAGE (V)
050
100 150
LT1083/4/5 ADJ G11
–25 25 75 125
TEMPERATURE (°C)
–50
100
90
80
70
60
50
40
30
20
10
0
ADJUST PIN CURRENT (µA)
050
100 150
LT1083/4/5 ADJ G12
–25 25 75 125
FREQUENCY (Hz)
RIPPLE REJECTION (dB)
100
90
80
70
60
50
40
30
20
10
010 1k 10k 100k
1083/4/5 ADJ G13
100
VRIPPLE
≤ 0.5VP-P
VRIPPLE ≤ 3VP-P
(VIN – VOUT) ≥ 3V
(VIN – VOUT) ≥ VDROPOUT
CADJ = 200µF AT FREQUENCIES < 60Hz
CADJ = 25µF AT FREQUENCIES > 60Hz
IOUT = 7A
OUTPUT CURRENT (A)
0
RIPPLE REJECTION (dB)
100
90
80
70
60
50
40
30
20
10
0245
1083/4/5 ADJ G14
13 678
V
OUT
= 5V
C
ADJ
= 25µF
C
OUT
= 25µF
f
R
= 120Hz
V
RIPPLE
≤ 3V
P-P
f
R
= 20kHz
V
RIPPLE
≤ 0.5V
P-P
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
LT1083 LT1083 LT1083
Ripple Rejection Ripple Rejection vs Current Maximum Power Dissipation*
LT1084 LT1084 LT1084
Ripple Rejection Ripple Rejection vs Current Maximum Power Dissipation*
FREQUENCY (Hz)
RIPPLE REJECTION (dB)
100
90
80
70
60
50
40
30
20
10
010 1k 10k 100k
1083/4/5 ADJ G16
100
VRIPPLE ≤ 0.5VP-P
VRIPPLE ≤ 3VP-P
(VIN – VOUT) ≥ 3V
(VIN – VOUT) ≥ VDROPOUT
CADJ = 200µF AT FREQUENCIES < 60Hz
CADJ = 25µF AT FREQUENCIES > 60Hz
IOUT = 5A
OUTPUT CURRENT (A)
0
RIPPLE REJECTION (dB)
100
90
80
70
60
50
40
30
20
10
0245
1083/4/5 ADJ G17
13
V
OUT
= 5V
C
ADJ
= 25µF
C
OUT
= 25µF
f
R
= 120Hz
V
RIPPLE
≤ 3V
P-P
f
R
= 20kHz
V
RIPPLE
≤ 0.5V
P-P
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
6
LT1083/LT1084/LT1085
TYPICAL PERFORMANCE CHARACTERISTICS
UW
TIME (µs)
0
OUTPUT VOLTAGE
DEVIATION (V)
LOAD CURRENT (A)
0.3
0.2
0.1
0
–0.1
–0.2
–0.3
3
2
1
050
1083/4/5 ADJ G24
100
C
ADJ
= 0
C
ADJ
= 1µF
C
IN
= 1µF
C
OUT
= 10µF TANTALUM
V
OUT
=10V
V
IN
=13V
PRELOAD=100mA
LT1085 LT1085 LT1085
Ripple Rejection Ripple Rejection vs Current Maximum Power Dissipation*
FREQUENCY (Hz)
RIPPLE REJECTION (dB)
100
90
80
70
60
50
40
30
20
10
010 1k 10k 100k
1083/4/5 ADJ G19
100
VRIPPLE
≤ 0.5VP-P
VRIPPLE ≤ 3VP-P
(VIN – VOUT) ≥ 3V
(VIN – VOUT) ≥ VDROPOUT
CADJ = 200µF AT FREQUENCIES < 60Hz
CADJ = 25µF AT FREQUENCIES > 60Hz
IOUT = 3A
OUTPUT CURRENT (A)
0
RIPPLE REJECTION (dB)
100
90
80
70
60
50
40
30
20
10
01.0 1.5 2.5 3.0
1083/4/5 ADJ G20
0.5 2.0
V
OUT
= 5V
C
ADJ
= 25µF
C
OUT
= 25µF
f
R
= 120Hz
V
RIPPLE
≤ 3V
P-P
f
R
= 20kHz
V
RIPPLE
≤ 0.5V
P-P
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
LT1083 LT1084 LT1085
Load Transient Response Load Transient Response Load Transient Response
TIME (µs)
0
OUTPUT VOLTAGE
DEVIATION (V)
LOAD CURRENT (A)
0.6
0.4
0.2
0
–0.2
–0.4
8
6
4
2
050
1083/4/5 ADJ G22
100
C
ADJ
= 0 C
ADJ
= 1µF
C
IN
= 1µF
C
OUT
= 10µF TANTALUM
V
OUT
=10V
V
IN
=13V
PRELOAD=100mA
TIME (µs)
0
OUTPUT VOLTAGE
DEVIATION (V)
LOAD CURRENT (A)
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
6
4
2
050
1083/4/5 ADJ G23
100
C
ADJ
= 0
C
ADJ
= 1µF
C
IN
= 1µF
C
OUT
= 10µF TANTALUM
V
OUT
=10V
V
IN
=13V
PRELOAD=100mA
LT1083 LT1084 LT1085
Line Transient Response Line Transient Response Line Transient Response
TIME (µs)
0
OUTPUT VOLTAGE
DEVIATION (V)
INPUT
DEVIATION (V)
60
40
20
0
–20
–40
–60
14
13
12
100
1083/4/5 ADJ G26
200
C
ADJ
= 0
C
ADJ
= 1µF
V
OUT
= 10V
I
IN
= 0.2A
C
IN
= 1µF TANTALUM
C
OUT
= 10µF TANTALUM
TIME (µs)
0
OUTPUT VOLTAGE
DEVIATION (mV)
INPUT
DEVIATION (V)
60
40
20
0
–20
–40
–60
14
13
12
100
1083/4/5 ADJ G27
200
C
ADJ
= 0
C
ADJ
= 1µF
V
OUT
= 10V
I
IN
= 0.2A
C
IN
= 1µF TANTALUM
C
OUT
= 10µF TANTALUM
TIME (µs)
0
OUTPUT VOLTAGE
DEVIATION (mV)
INPUT
DEVIATION (V)
150
100
50
0
–50
–100
–150
14
13
12
100
1083/4/5 ADJ G25
200
C
ADJ
= 0
C
ADJ
= 1µF
V
OUT
= 10V
I
IN
= 0.2A
C
IN
= 1µF TANTALUM
C
OUT
= 10µF TANTALUM
7
LT1083/LT1084/LT1085
BLOCK DIAGRAM
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APPLICATIONS INFORMATION
WUUU
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 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.
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
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.
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.
Recommended Capacitor Values
INPUT OUTPUT ADJUSTMENT
10µF10µF Tantalum, 50µF Aluminum None
10µF22µF Tantalum, 150µF Aluminum 20µF
–
+
THERMAL
LIMIT
V
ADJ
V
OUT
1083/4/5 ADJ BD
V
IN
8
LT1083/LT1084/LT1085
APPLICATIONS INFORMATION
WUUU
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, exceed-
ing the maximum input to output voltage differential
causes the internal transistors to break down and none of
the protection circuitry is functional.
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 capacitor 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 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
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. Older adjustable regulators required
protection diodes between the adjustment pin and the
output and from the output to the input to prevent over-
stressing 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 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
R1
R2
IN OUT
ADJ
V
OUT
LT1083
D1
1N4002
(OPTIONAL)
V
IN
1083/4/5 ADJ F00
C
OUT
150µF
+
C
ADJ
10µF
+
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
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.
9
LT1083/LT1084/LT1085
APPLICATIONS INFORMATION
WUUU
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
/V
REF
). For example,
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 de-
graded 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
ADJ
is very small and constant when compared
with the current through R1, it represents a small error and
can usually be ignored.
Figure 1. Basic Adjustable Regulator
R1
R2
IN OUT
I
ADJ
50µA
ADJ
V
OUT
LT1083
V
IN
1083/4/5 ADJ F01
V
REF
V
OUT
= V
REF
1 + + I
ADJ
R2
R2
R1
( )
Load Regulation
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:
RRR
RR Parasitic Line
PP
×+
=
21
1, Resistance
Figure 2. Connections for Best Load Regulation
LT1083 OUTINV
IN
ADJ
R
P
PARASITIC
LINE RESISTANCE
R1*
*CONNECT R1 TO CASE
CONNECT R2 TO LOAD
1083/4/5 ADJ F02
R
L
R2*
10
LT1083/LT1084/LT1085
APPLICATIONS INFORMATION
WUUU
Connected as shown, R
P
is not multiplied by the divider
ratio. R
P
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 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
new regulators provides a separate thermal resistance and
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.
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 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:
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.
11
LT1083/LT1084/LT1085
TYPICAL APPLICATIONS
U
7.5A Variable Regulator
15V
15V
15V
110VAC
T1
TRIAD
F-269U
–
+
–
+
++
–
+
OUTIN LT1083 OUTIN
ADJ
C30B
C30B
3
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*
LT1004-1.2
11k*
11k*
0V TO 35V
OA 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
750Ω*
2k
OUTPUT
ADJUST
2.7k
–15V
1.5k
15K
10k
2N3904
NC
8
6
7
1
LT1011
LT1011
LM301A
* 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
LT1083/4/5 ADJ TA05
12
LT1083/LT1084/LT1085
TYPICAL APPLICATIONS
U
LT1083 OUTINV
IN
ADJ
LT1083
0.015Ω
OUT
2 FEET #18 WIRE*
IN
ADJ
R1
120Ω
R2
*THE #18 WIRE ACTS
AS BALLAST RESISTANCE
INSURING CURRENT SHARING
BETWEEN BOTH DEVICES
LT1083/4/5 ADJ TA03
V
OUT
= 1.25V 1 +
I
OUT
= 0A TO 15A
R2
R1
()
Paralleling Regulators
Remote Sensing
R1
121Ω
1%
IN OUT
ADJ
R2
365Ω
1%
10µF
VOUT
5V
LT1083
VIN
1083/4/5 ADJ TA04
+
C1
25µF*
150µF
+
+
*C1 IMPROVES RIPPLE REJECTION.
XC SHOULD BE < R1 AT RIPPLE FREQUENCY
Improving Ripple Rejection
–
+
LT1083 OUTIN
V
IN
V
IN
RETURN
ADJ
R
P
(MAX DROP 300mV)
121Ω
365Ω
25Ω
10µF
5µF
100µF
1083/4/5 ADJ TA07
R
L
V
OUT
5V
RETURN
25Ω
2
6
7
1
8
100pF
3
4
+
+
+
1k
LM301A
13
LT1083/LT1084/LT1085
TYPICAL APPLICATIONS
U
High Efficiency Regulator with Switching Preregulator
+
–
+
VIN
28V
28V
470Ω240Ω
2k
28V
4N28
1N914
1N914
LT1011
10k
10k
10k
1k 1M
MR1122
1mH
10,000µF
VOUT
LT1083 OUTIN
ADJ
1083/4/5 ADJ TA06
1.2V to 15V Adjustable Regulator
5V Regulator with Shutdown*
IN
V
IN
OUT
TTL
ADJ
1k
1k
10µF
100µF
V
OUT
5V
LT1083
2N3904
1083/4/5 ADJ TA09
+
121Ω
1%
365Ω
1%
+
*OUTPUT SHUTS DOWN TO 1.3V
IN OUT
ADJ
R2
1k
C1*
10µF
V
OUT†
V
IN
LT1083
1083/4/5 ADJ TA08
+
C2
100µF
+
R1
90.9Ω
*NEEDED IF DEVICE IS FAR FROM FILTER CAPACITORS
†
V
OUT
= 1.25V 1 + R2
R1
()
14
LT1083/LT1084/LT1085
Dimension in inches (millimeters) unless otherwise noted.
PACKAGE DESCRIPTION
U
K2 (TO-3) 1098
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)
0.490 – 0.510
(12.45 – 12.95)
R
0.167 – 0.177
(4.24 – 4.49)
R
0.151 – 0.161
(3.86 – 4.09)
DIA, 2PLCS
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)
M (DD3) 1098
0.050
(1.270)
BSC
0.143+0.012
–0.020
()
3.632+0.305
–0.508
0.090 – 0.110
(2.286 – 2.794) 0.013 – 0.023
(0.330 – 0.584)
0.095 – 0.115
(2.413 – 2.921)
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
0.045 – 0.055
(1.143 – 1.397)
0.165 – 0.180
(4.191 – 4.572)
0.330 – 0.370
(8.382 – 9.398)
0.060
(1.524)
TYP
0.390 – 0.415
(9.906 – 10.541)
15° TYP
0.300
(7.620)
0.075
(1.905)
0.183
(4.648)
0.060
(1.524)
0.060
(1.524)
0.256
(6.502)
BOTTOM VIEW OF DD PAK
HATCHED AREA IS SOLDER PLATED
COPPER HEAT SINK
K Package
2-Lead TO-3 Metal Can
(LTC DWG # 05-08-1310)
M Package
3-Lead Plastic DD Pak
(LTC DWG # 05-08-1460)
15
LT1083/LT1084/LT1085
Dimension in inches (millimeters) unless otherwise noted.
PACKAGE DESCRIPTION
U
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.
0.580 – 0.6OO
(14.73 – 15.24)
0.170
(4.32)
MAX
0.325
(8.255)
0.580
(14.732)
0.560
(14.224) 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 0996
0.098
(2.489)
0.124
(3.149)
0.700
(17.780)
0.275
(6.985)
BOTTOM VIEW OF TO-3P
HATCHED AREA IS SOLDER PLATED
COPPER HEAT SINK
0.100
(2.540)
BSC 0.028 – 0.038
(0.711 – 0.965)
T3 (TO-220) 1098
0.045 – 0.055
(1.143 – 1.397)
0.165 – 0.180
(4.191 – 4.572)
0.095 – 0.115
(2.413 – 2.921)
0.013 – 0.023
(0.330 – 0.584)
0.520 – 0.570
(13.208 – 14.478)
0.980 – 1.070
(24.892 – 27.178)
0.218 – 0.252
(5.537 – 6.401)
0.050
(1.270)
TYP
0.147 – 0.155
(3.734 – 3.937)
DIA
0.390 – 0.415
(9.906 – 10.541)
0.330 – 0.370
(8.382 – 9.398)
0.460 – 0.500
(11.684 – 12.700)
0.570 – 0.620
(14.478 – 15.748)
0.230 – 0.270
(5.842 – 6.858)
T Package
3-Lead Plastic TO-220
(LTC DWG # 05-08-1420)
P Package
3-Lead Plastic TO-3P (Similar to TO-247)
(LTC DWG # 05-08-1450)
16
LT1083/LT1084/LT1085
1083fds, sn1083 LT/TP 0200 2K REV D • PRINTED IN USA
LINEAR T ECHNOLOGY C ORPORATION 1994
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear-tech.com
TYPICAL APPLICATIONS
U
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
OUT
and Adjustable
LT1581 10A Very Low Dropout Linear Regulator 0.43V Dropout at 10A, Fixed 2.5V
OUT
and Adjustable
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.
RELATED PARTS
Automatic Light Control
Protected High Current Lamp Driver
IN
V
IN
OUT
ADJ
10µF100µF
LT1083
1083/4/5 ADJ TA10
1.2k
+
OUT
TTL OR
CMOS
IN
ADJ
15V
12V
5A
LT1083
1083/4/5 ADJ TA11
10k
