LT1083/LT1084/LT1085
1
108345fg
TYPICAL APPLICATION
DESCRIPTION
7.5A, 5A, 3A Low Dropout
Positive Adjustable Regulators
The LT®1083 series of positive adjustable regulators are
designed to provide 7.5A, 5A and 3A with higher effi ciency
than currently available devices. All internal circuitry is
designed to operate down to 1V input-to-output differential
and the dropout voltage is fully specifi ed as a function of
load current. Dropout is guaranteed at a maximum of 1.5V
at maximum output current, decreasing at lower load cur-
rents. 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 3-terminal regulators. A 10μF output capacitor
is required on these new devices. However, this is included
in most regulator designs.
Unlike PNP regulators, where up to 10% of the output cur-
rent is wasted as quiescent current, the LT1083 quiescent
current fl ows into the load, increasing effi ciency.
FEATURES
APPLICATIONS
n 3-Terminal Adjustable
n Output Current of 3A, 5A or 7.5A
n Operates Down to 1V Dropout
n Guaranteed Dropout Voltage at Multiple Current Levels
n Line Regulation: 0.015%
n Load Regulation: 0.1%
n 100% Thermal Limit Functional Test
n Fixed Versions Available
n Available in 3-Lead Plastic TO-220, TO-3P and DD
Packages
n High Effi ciency Linear Regulators
n Post Regulators for Switching Supplies
n Constant Current Regulators
n Battery Chargers
DEVICE OUTPUT CURRENT*
LT1083
LT1084
LT1085
7.5A
5.0A
3.0A
*For a 1.5A low dropout regulator see the LT1086 data sheet.
, LT, LTM and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
121Ω
1%
IN OUT
ADJ
365Ω
1%
10μF
5V AT 7.5A
LT1083
VIN ≥ 6.5V
1083/4/5 ADJ TA01
+
10μF*
TANTALUM
+
*REQUIRED FOR STABILITY
5V, 7.5A Regulator
OUTPUT CURRENT
0
INPUT/OUTPUT VOLTAGE DIFFERENTIAL (V)
2
1
0
1083/4/5 ADJ TA02
I
FULL LOAD
Dropout Voltage vs Output Current
LT1083/LT1084/LT1085
2
108345fg
PRECONDITIONING
ABSOLUTE MAXIMUM RATINGS
Power Dissipation ................................Internally Limited
Input-to-Output Voltage Differential
C-Grades ..............................................................30V
I-Grades ................................................................30V
M-Grades (OBSOLETE) ......................................... 35V
Operating Junction Temperature Range (Note 9)
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: (OBSOLETE)
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.
(Note 1)
T PACKAGE
3-LEAD PLASTIC TO-220
FRONT VIEW
TAB
IS
OUTPUT
3
2
1
VIN
VOUT
ADJ
θJA = 50°C/W
VIN
VOUT
ADJ
P PACKAGE
3-LEAD PLASTIC TO-3P
FRONT VIEW
TAB IS
OUTPUT
3
2
1
θJA = 35°C/W
1
2
VIN CASE IS
OUTPUT
BOTTOM VIEW
ADJ
K PACKAGE
2-LEAD TO-3 METAL CAN
θJA = 35°C/W
OBSOLETE PACKAGE
VIN
VOUT
ADJ
3
2
1
M PACKAGE
3-LEAD PLASTIC DD
FRONT VIEW
TAB
IS
OUTPUT
3
2
1
θJA = 30°C/W*
*WITH PACKAGE SOLDERED TO 0.5IN2 COPPER AREA OVER
BACKSIDE GROUND PLANE OR INTERNAL POWER PLANE. θJA CAN VARY
FROM 20°C/W TO >40°C/W DEPENDING ON MOUNTING TECHNIQUE
PIN CONFIGURATION
LT1083/LT1084/LT1085
3
108345fg
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LT1083CP#PBF LT1083CP#TRPBF LT1083CP 3-Lead Plastic TO-3P Control: 0°C to 125°C
Power: 0°C to 150°C
LT1084CP#PBF LT1084CP#TRPBF LT1084CP 3-Lead Plastic TO-3P Control: 0°C to 125°C
Power: 0°C to 150°C
LT1084CT#PBF LT1084CT#TRPBF LT1084CT 3-Lead Plastic TO-220 Control: 0°C to 125°C
Power: 0°C to 150°C
LT1084IT#PBF LT1084IT#TRPBF LT1084IT 3-Lead Plastic TO-220 Control: –40°C to 125°C
Power: –40°C to 150°C
LT1085CT#PBF LT1085CT#TRPBF LT1085CT 3-Lead Plastic TO-220 Control: 0°C to 125°C
Power: 0°C to 150°C
LT1085IT#PBF LT1085IT#TRPBF LT1085IT 3-Lead Plastic TO-220 Control: –40°C to 125°C
Power: –40°C to 150°C
LT1085CM#PBF LT1085CM#TRPBF LT1085CM 3-Lead Plastic DD Control: 0°C to 125°C
Power: 0°C to 150°C
LT1085IM#PBF LT1085IM#TRPBF LT1085IM 3-Lead Plastic DD Control: –40°C to 125°C
Power: –40°C to 150°C
LEAD BASED FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LT1083CP LT1083CP#TR LT1083CP 3-Lead Plastic TO-3P Control: 0°C to 125°C
Power: 0°C to 150°C
LT1084CP LT1084CP#TR LT1084CP 3-Lead Plastic TO-3P Control: 0°C to 125°C
Power: 0°C to 150°C
LT1084CT LT1084CT#TR LT1084CT 3-Lead Plastic TO-220 Control: 0°C to 125°C
Power: 0°C to 150°C
LT1084IT LT1084IT#TR LT1084IT 3-Lead Plastic TO-220 Control: –40°C to 125°C
Power: –40°C to 150°C
LT1085CT LT1085CT#TR LT1085CT 3-Lead Plastic TO-220 Control: 0°C to 125°C
Power: 0°C to 150°C
LT1085IT LT1085IT#TR LT1085IT 3-Lead Plastic TO-220 Control: –40°C to 125°C
Power: –40°C to 150°C
LT1085CM LT1085CM#TR LT1085CM 3-Lead Plastic DD Control: 0°C to 125°C
Power: 0°C to 150°C
LT1085IM LT1085IM#TR LT1085IM 3-Lead Plastic DD Control: –40°C to 125°C
Power: –40°C to 150°C
LT1083CK LT1083CK#TR LT1083CK 2-Lead TO-3 Metal Can Control: 0°C to 125°C
Power: 0°C to 150°C
LT1083MK LT1083MK#TR LT1083MK 2-Lead TO-3 Metal Can Control: –55°C to 150°C
Power: –55°C to 200°C
LT1084CK LT1084CK#TR LT1084CK 2-Lead TO-3 Metal Can Control: 0°C to 125°C
Power: 0°C to 150°C
LT1084MK LT1084MK#TR LT1084MK 2-Lead TO-3 Metal Can Control: –55°C to 150°C
Power: –55°C to 200°C
LT1085CK LT1085CK#TR LT1085CK 2-Lead TO-3 Metal Can Control: 0°C to 125°C
Power: 0°C to 150°C
LT1085MK LT1085MK#TR LT1085MK 2-Lead TO-3 Metal Can Control: –55°C to 150°C
Power: –55°C to 200°C
OBSOLETE PACKAGE
Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. *The temperature grade is identifi ed by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifi cations, go to: http://www.linear.com/tapeandreel/
LT1083/LT1084/LT1085
4
108345fg
ELECTRICAL CHARACTERISTICS
The l denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at TA = 25°C.
PARAMETER CONDITIONS MIN TYP MAX UNITS
Reference Voltage IOUT = 10mA, TJ = 25°C,
(VIN – VOUT) = 3V
10mA ≤ IOUT ≤ IFULL_LOAD
1.5V ≤ (VIN – VOUT) ≤ 25V (Notes 4, 6, 7) l
1.238
1.225
1.250
1.250
1.262
1.270
V
V
Line Regulation ILOAD = 10mA, 1.5V ≤ (VIN – VOUT) ≤ 15V, TJ = 25°C (Notes 2, 3)
l
0.015
0.035
0.2
0.2
%
%
M-Grade: 15V ≤ (VIN – VOUT) ≤ 35V (Notes 2, 3) l0.05 0.5 %
C-, I-Grades: 15V ≤ (VIN – VOUT) ≤ 30V (Notes 2, 3) l0.05 0.5 %
Load Regulation (VIN – VOUT) = 3V, 10mA ≤ IOUT ≤ IFULL_LOAD, TJ = 25°C
(Notes 2, 3, 4, 6) l
0.1
0.2
0.3
0.4
%
%
Dropout Voltage ΔVREF = 1%, IOUT = IFULL_LOAD (Notes 5, 6, 8) l1.3 1.5 V
Current Limit
LT1083
LT1084
LT1085
(VIN – VOUT) = 5V
(VIN – VOUT) = 25V
(VIN – VOUT) = 5V
(VIN – VOUT) = 25V
(VIN – VOUT) = 5V
(VIN – VOUT) = 25V
l
l
l
l
l
l
8.0
0.4
5.5
0.3
3.2
0.2
9.5
1.0
6.5
0.6
4.0
0.5
A
A
A
A
A
A
Minimum Load Current (VIN – VOUT) = 25V l510 mA
Thermal Regulation
LT1083
LT1084
LT1085
TA = 25°C, 30ms Pulse
0.002
0.003
0.004
0.010
0.015
0.020
%/W
%/W
%/W
Ripple Rejection f = 120Hz, CADJ = 25μF, COUT = 25μF Tantalum
IOUT = IFULL_LOAD, (VIN – VOUT) = 3V (Notes 6, 7, 8)
l60 75 dB
Adjust Pin Current TJ = 25°C
l
55
120
μA
μA
Adjust Pin Current Change 10mA ≤ IOUT ≤ IFULL_LOAD, 1.5V ≤ (VIN – VOUT) ≤ 25V (Note 6) l0.2 5 μA
Temperature Stability l0.5 %
Long-Term Stability TA = 125°C, 1000 Hrs 0.3 1 %
RMS Output Noise (% of VOUT)T
A = 25°C, 10Hz = ≤ f ≤ 10kHz 0.003 %
LT1083/LT1084/LT1085
5
108345fg
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: See thermal regulation specifi cations 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 voltage
range.
Note 4: IFULL_LOAD is defi ned in the current limit curves. The IFULL_LOAD
curve is defi ned 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 specifi ed over the full output current range of
the device. Test points and limits are shown on the Dropout Voltage
curve.
Note 6: For LT1083 IFULL_LOAD is 5A for –55°C ≤ TJ < – 40°C and 7.5A for
TJ ≥ –40°C.
Note 7: 1.7V ≤ (VIN – VOUT) ≤ 25V for LT1084 at –55°C ≤ TJ ≤ – 40°C.
Note 8: Dropout is 1.7V maximum for LT1084 at –55°C ≤ TJ ≤ –40°C.
Note 9: The LT1083/LT1084/LT1085 regulators are tested and specifi ed
under pulse load conditions such that TJ ≅ TA. The C-grade LT1083/
LT1084/LT1085 are 100% tested at 25°C.The I-grade LT1084/LT1085 are
guaranteed over the full –40°C to 125°C operating ambient temperature
range.
ELECTRICAL CHARACTERISTICS
The l denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at TA = 25°C.
PARAMETER CONDITIONS MIN TYP MAX UNITS
Thermal Resistance Junction-to-Case
LT1083
LT1084
LT1085
Control Circuitry/Power Transistor
K Package
P Package
K Package
P Package
T Package
K Package
M, T Package
0.6/1.6
0.5/1.6
0.75/2.3
0.65/2.3
0.65/2.7
0.9/3.0
0.7/3.0
°C/W
°C/W
°C/W
°C/W
°C/W
°C/W
°C/W
LT1083/LT1084/LT1085
6
108345fg
TYPICAL PERFORMANCE CHARACTERISTICS
OUTPUT CURRENT (A)
0
MINIMUM INPUT/OUTPUT DIFFERENTIAL (V)
1
2
LT1083/4/5 ADJ G01
012345678910
INDICATES GUARANTEED TEST POINT
–40°C ≤ TJ ≤ 150°C
0°C ≤ TJ ≤ 125°C
TJ = 150°C
TJ = 25°C
TJ = –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
ΔI = 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 ≤ TJ ≤ 150°C
0°C ≤ TJ ≤ 125°C
TJ = 150°C
TJ = –55°C
TJ = 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
IFULL 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
ΔI = 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
ΔI = 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
LT1083
Dropout Voltage
LT1083
Short-Circut Current
LT1083
Load Regulation
LT1084
Dropout Voltage
LT1084
Short-Circut Current
LT1084
Load Regulation
LT1085
Dropout Voltage
LT1085
Short-Circuit Current
LT1085
Load Regulation
LT1083/LT1084/LT1085
7
108345fg
TYPICAL PERFORMANCE CHARACTERISTICS
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
TJ = –55°C
TJ = 150°C
TJ = 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
0
245
1083/4/5 ADJ G14
13 678
VOUT = 5V
CADJ = 25μF
COUT = 25μF
fR = 120Hz
VRIPPLE ≤ 3VP-P
fR = 20kHz
VRIPPLE ≤ 0.5VP-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
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
0
245
1083/4/5 ADJ G17
13
VOUT = 5V
CADJ = 25μF
COUT = 25μF
fR = 120Hz
VRIPPLE ≤ 3VP-P
fR = 20kHz
VRIPPLE ≤ 0.5VP-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
Minimum Operating Current Temperature Stability Adjust Pin Current
LT1083
Ripple Rejection
LT1083
Ripple Rejection vs Current
LT1083
Maximum Power Dissipation*
LT1084
Maximum Power Dissipation*
LT1084
Ripple Rejection vs Current
LT1084
Ripple Rejection
LT1083/LT1084/LT1085
8
108345fg
TYPICAL PERFORMANCE CHARACTERISTICS
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
0
50
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
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
0
1.0 1.5 2.5 3.0
1083/4/5 ADJ G20
0.5 2.0
VOUT = 5V
CADJ = 25μF
COUT = 25μF
fR = 120Hz
VRIPPLE ≤ 3VP-P
fR = 20kHz
VRIPPLE ≤ 0.5VP-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
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
0
50
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
0
50
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
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 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
LT1085
Ripple Rejection
LT1085
Ripple Rejection vs Current
LT1085
Maximum Power Dissipation*
LT1083
Load Transient Response
LT1084
Load Transient Response
LT1085
Load Transient Response
LT1083
Line Transient Response
LT1084
Line Transient Response
LT1085
Line Transient Response
LT1083/LT1084/LT1085
9
108345fg
BLOCK DIAGRAM
APPLICATIONS INFORMATION
–
+
THERMAL
LIMIT
VADJ
VOUT
1083/4/5 ADJ BD
VIN
The LT1083 family of 3-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 3-terminal
adjustable devices, offer lower dropout voltage and more
precise reference tolerance. Further, the reference stability
with temperature is improved over older types of regula-
tors. 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
a 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
capacitors 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
10μF
10μF
10μF Tantalum, 50μF Aluminum
22μF Tantalum, 150μF Aluminum
None
20μF
LT1083/LT1084/LT1085
10
108345fg
APPLICATIONS INFORMATION
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 deg-
radation. 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.
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 volt-
age 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 un-
stable. 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 re-
quired 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 cur-
rents of 50A to 100A. Even with large output capacitances,
it is very diffi cult 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 input
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 fi rst 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.
LT1083/LT1084/LT1085
11
108345fg
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 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
The typical curves for ripple rejection refl ect 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 (VOUT/VREF). 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 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 fl ow through R1 and down
through R2 to set the overall output voltage. Normally this
current is the specifi ed minimum load current of 10mA.
Because IADJ is very small and constant when compared
with the current through R1, it represents a small error
and can usually be ignored.
Load Regulation
Because the LT1083 is a 3-terminal device, it is not pos-
sible 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 specifi cation 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 resis-
tor 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 between the regulator
and the load would be:
RRR
RR Parasitic Line
PP
•,
21
1
+
⎛
⎝
⎜⎞
⎠
⎟=Resistannce
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
( )
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*
LT1083/LT1084/LT1085
12
108345fg
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 im-
portant 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 specifi cations have been developed to
more accurately refl ect 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 specifi cation,
used an average of the two values provided here and there-
fore 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 specifi ed from the
IC junction to the bottom of the case directly below the
die. This is the lowest resistance path for heat fl ow. Proper
mounting is required to ensure the best possible thermal
fl ow 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, VOUT = 5V, IOUT = 6A,
T
A = 75°C, θHEAT SINK = 1°C/W,
θCASE-TO-HEAT SINK = 0.2°C/W for K package with
thermal compound.
Power dissipation under these conditions is equal to:
P
D = (VIN – VOUT )(IOUT) = 24W
Junction temperature will be equal to:
T
J = TA + PD (θHEAT SINK + θCASE-TO-HEAT SINK + θJC)
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 = TJMAX (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 = TJMAX (Power Transistor
Commercial Range)
In both cases the junction temperature is below the maxi-
mum rating for the respective sections, ensuring reliable
operation.
LT1083/LT1084/LT1085
13
108345fg
TYPICAL APPLICATION
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
560Ω
16k*
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
LT1083/LT1084/LT1085
14
108345fg
TYPICAL APPLICATION
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
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
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
+
+
LT1083/LT1084/LT1085
15
108345fg
TYPICAL APPLICATION
High Effi ciency Regulator with Switching Preregulator
–
+
V
IN
28V
28V
470Ω
240Ω
2k
28V
4N28
1N914
1N914
LT1011
10k
10k
10k
1k 1M
MR1122
1mH
10,000μF
V
OUT
LT1083 OUTIN
ADJ
1083/4/5 ADJ TA06
+
1.2V to 15V Adjustable Regulator
5V Regulator with Shutdown*
IN
VIN OUT
TTL
ADJ
1k
1k
10μF
100μF
VOUT
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
()
LT1083/LT1084/LT1085
16
108345fg
PACKAGE DESCRIPTION
OBSOLETE PACKAGE
.050
(1.270)
.143 +.012
–.020
()
3.632 +0.305
–0.508
.100
(2.54)
BSC
.013 – .023
(0.330 – 0.584)
.095 – .115
(2.413 – 2.921)
.004 +.008
–.004
()
0.102 +0.203
–0.102
.050 ± .012
(1.270 ± 0.305)
.059
(1.499)
.045 – .055
(1.143 – 1.397)
.165 – .180
(4.191 – 4.572)
.330 – .370
(8.382 – 9.398)
.060
(1.524)
TYP
.390 – .415
(9.906 – 10.541)
15°
.300
(7.620)
.075
(1.905)
.183
(4.648)
.060
(1.524)
.060
(1.524)
.256
(6.502)
BOTTOM VIEW OF DD PAK
HATCHED AREA IS SOLDER PLATED
COPPER HEAT SINK
M (DD3) 0204
.420
.350
.565
.090
.070
.100
.420
.276
.325
.205
.080
.565
.090
.070
.100
RECOMMENDED SOLDER PAD LAYOUT
FOR THICKER SOLDER PASTE APPLICATIONS
RECOMMENDED SOLDER PAD LAYOUT
NOTE:
1. DIMENSIONS IN INCH/(MILLIMETER)
2. DRAWING NOT TO SCALE
.320
K2 (TO-3) 080
.038 – .043
(0.965 – 1.09)
.060 – .135
(1.524 – 3.429)
.320 – .350
(8.13 – 8.89)
.420 – .480
(10.67 – 12.19)
.760 – .775
(19.30 – 19.69)
.490 – .510
(12.45 – 12.95)
R
.167 – .177
(4.24 – 4.49)
R
.151 – .161
(3.86 – 4.09)
DIA, 2PLCS
1.177 – 1.197
(29.90 – 30.40)
.655 – .675
(16.64 – 17.15)
.067 – .077
(1.70 – 1.96)
.210 – .220
(5.33 – 5.59)
.425 – .435
(10.80 – 11.05)
K Package
2-Lead TO-3 Metal Can
(Reference LTC DWG # 05-08-1310)
M Package
3-Lead Plastic DD Pak
(Reference LTC DWG # 05-08-1460)
LT1083/LT1084/LT1085
17
108345fg
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
PACKAGE DESCRIPTION
.170
(4.32)
MAX
.325
(8.255)
.580
(14.732)
.560
(14.224)
.170 – .2OO
(4.32 – 5.08)
MOUNTING HOLE
.115 – .145
(2.92 – 3.68)
DIA
.580 – .6OO
(14.73 – 15.24)
.830 – .870
(21.08 – 22.10)
.780 – .800
(19.81 – 20.32)
.620 – .64O
(15.75 – 16.26)
.215
(5.46)
BSC
.113 – .123
(2.87 – 3.12)
.042 – .052
(1.07 – 1.32)
.074 – .084
(1.88 – 2.13)
.187 – .207
(4.75 – 5.26)
.060 – .080
(1.52 – 2.03)
18° – 22°
3° – 7°
.087 – .102
(2.21 – 2.59)
.020 – .040
(0.51 – 1.02)
EJECTOR PIN MARKS
.105 – .125
(2.67 – 3.18)
DIA
P3 0801
.098
(2.489)
.124
(3.149)
.700
(17.780)
.275
(6.985)
BOTTOM VIEW OF TO-3P
HATCHED AREA IS SOLDER PLATED
COPPER HEAT SINK
.100
(2.540)
BSC .028 – .038
(0.711 – 0.965)
T3 (TO-220) 0801
.045 – .055
(1.143 – 1.397)
.165 – .180
(4.191 – 4.572)
.095 – .115
(2.413 – 2.921)
.013 – .023
(0.330 – 0.584)
.520 – .570
(13.208 – 14.478)
.980 – 1.070
(24.892 – 27.178)
.218 – .252
(5.537 – 6.401)
.050
(1.270)
TYP
.147 – .155
(3.734 – 3.937)
DIA
.390 – .415
(9.906 – 10.541)
.330 – .370
(8.382 – 9.398)
.460 – .500
(11.684 – 12.700)
.570 – .620
(14.478 – 15.748)
.230 – .270
(5.842 – 6.858)
P Package
3-Lead Plastic TO-3P (Similar to TO-247)
(Reference LTC DWG # 05-08-1450)
T Package
3-Lead Plastic TO-220
(Reference LTC DWG # 05-08-1420)
LT1083/LT1084/LT1085
18
108345fg
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 1994
LT 0409 REV G • PRINTED IN USA
RELATED PARTS
TYPICAL APPLICATIONS
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 2.5VOUT and Adjustable
LT1581 10A Very Low Dropout Linear Regulator 0.43V Dropout at 10A, Fixed 2.5VOUT and Adjustable
LT1430 High Power Step-Down Switching Regulator 5V to 3.3V at 10A, >90% Effi ciency
LT1575 UltraFast™ 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.
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