1
LT1083/LT1084/LT1085 Fixed
1083ffd
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 LT
®
1083 series of positive adjustable regulators are
designed to provide 3A, 5A and 7.5A with higher efficiency
than currently available devices. All internal circuitry is
designed to operate down to 1V input to output differential
and the dropout voltage is fully specified as a function of
load current. Dropout is guaranteed at a maximum of 1.5V
at maximum output current, decreasing at lower load
currents. On-chip trimming adjusts the output voltage to
1%. Current limit is also trimmed, minimizing the stress
on both the regulator and power source circuitry under
overload conditions.
The LT1083 series devices are pin compatible with older
three-terminal regulators. A 10μF output capacitor is
required on these new devices; however, this is usually
included in most regulator designs.
Unlike PNP regulators, where up to 10% of the output
current is wasted as quiescent current, the LT1083 quies-
cent current flows into the load, increasing efficiency.
3A, 5A, 7.5A Low Dropout
Positive Fixed Regulators
■
High Efficiency Linear Regulators
■
Post Regulators for Switching Supplies
■
Constant Current Regulators
■
Battery Chargers
5V, 7.5A Regulator Dropout Voltage vs Output Current
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
VIN ≥ 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
IFULLLOAD/2 IFULLLOAD
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
2
LT1083/LT1084/LT1085 Fixed
1083ffd
TAB IS
OUTPUT
T PACKAGE
3-LEAD PLASTIC TO-220
V
IN
V
OUT
GND
FRONT VIEW
3
2
1
Power Dissipation.............................. Internally Limited
Input Voltage* ........................................................ 30V
Operating Input Voltage
3.3V, 3.6V Devices ........................................... 20V
5V Devices ....................................................... 20V
12V Devices ..................................................... 25V
Operating Junction Temperature Range
“C” Grades
Control Section .............................. 0°C to 125°C
Power Transistor ............................ 0°C to 150°C
“M” Grades
Control Section .......................... –55°C to 150°C
Power Transistor ........................ –55°C to 200°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
100% Thermal Limit Functional Test.
*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.
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
LT1084CT-3.3
LT1084CT-5
LT1084CT-12
LT1085CT-3.3
LT1085CT-3.6
LT1085CT-5
LT1085CT-12
LT1085CM-3.3
LT1085CM-3.6
LT1085IM-3.6
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.
ABSOLUTE AXI U RATI GS
WWWU
(Note 1)
PRECO DITIO I G
U
UU
PACKAGE/ORDER I FOR ATIO
UU
W
1
2
V
IN
CASE IS
OUTPUT
GND
K PACKAGE
2-LEAD TO-3 METAL CAN
VIN
VOUT
GND
P PACKAGE
3-LEAD TO-3P PLASTIC
FRONT VIEW
TAB IS
OUTPUT
3
2
1
ORDER PART NUMBER
TAB IS
OUTPUT
M PACKAGE
3-LEAD PLASTIC DD
FRONT VIEW
VIN
VOUT
GND
3
2
1
OBSOLETE NOT RECOMMENDED
FOR NEW DESIGNS
Consult factory for parts specified with wider operating temperature ranges.
3
LT1083/LT1084/LT1085 Fixed
1083ffd
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
4.8V ≤ V
IN
≤ 15V, 0 ≤ I
OUT
≤ I
FULLOAD
(Notes 3, 4, 9) ●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
≤ I
FULLOAD
(Notes 3, 4, 9) ●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
≤ I
FULLOAD
(Note 9) ●3.500 3.672 V
5V ≤ V
IN
≤ 15V, 0 ≤ I
OUT
≤ I
FULLOAD
, TJ ≥ 0°C (Notes 3, 4, 9) 3.528 3.672 V
LT1085-3.6 5V ≤ V
IN
≤ 15V, 0 ≤ I
OUT
≤ 2.5A (Notes 3, 4, 9) ●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 4, 6, 7, 9) 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 4, 6, 7, 9) 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 2, 3) 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 2, 3) 1.0 25 mV
●2.0 25 mV
Load Regulation LT1084-3.3 V
IN
= 5V, 0 ≤ I
OUT
≤ 5A, T
J
= 25°C315mV
●720 mV
LT1085-3.3 V
IN
= 5V, 0 ≤ I
OUT
≤ 3A, T
J
= 25°C315mV
●720 mV
LT1085-3.6 V
IN
= 5.25V, 0 ≤ I
OUT
≤ 3A, T
J
= 25°C315mV
●720 mV
LT1083/4/5-5 V
IN
= 8V, 0 ≤ I
OUT
≤ I
FULLLOAD,
T
J
= 25°C (Notes 2, 3, 4, 6) 5 20 mV
●10 35 mV
LT1083/4/5-12 V
IN
= 15V, 0 ≤ I
OUT
≤ I
FULLLOAD,
T
J
= 25°C (Notes 2, 3, 4, 6) 12 36 mV
●24 72 mV
Dropout Voltage LT1084/5-3.3 ΔV
OUT
= 33mV, I
OUT
= I
FULL LOAD
(Notes 5, 6) ●1.3 1.5 V
LT1085-3.6 ΔV
OUT
= 36mV, I
OUT
= I
FULL LOAD
(Notes 5, 6) ●1.3 1.5 V
LT1083/4/5-5 ΔV
OUT
= 50mV, I
OUT
= I
FULL LOAD
(Notes 5, 6) ●1.3 1.5 V
LT1083/4/5-12 ΔV
OUT
= 120mV, I
OUT
= I
FULL LOAD
(Notes 5, 6) ●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
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
4
LT1083/LT1084/LT1085 Fixed
1083ffd
PARAMETER CONDITIONS MIN TYP MAX UNITS
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
(Note 4)
LT1084-3.3 f = 120Hz, C
OUT
= 25μF Tantalum, I
OUT
= 5A, V
IN
= 6.3V ●60 72 dB
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 6) ●60 68 dB
LT1083/4/5-12 V
IN
= 15V (Note 6) ●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
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 voltage 1.7V maximum for LT1084 at
–55°C ≤ T
J
≤ –40°C.
Note 9: Full load current is not available at all input-output voltages.
See Notes 3, 4, 6.
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 specifications for changes in output voltage
due to heating effects. Load and line regulation are measured at a constant
junction temperature by low duty cycle pulse testing.
Note 3: Line and load regulation are guaranteed up to the maximum power
dissipation (60W for the LT1083, 45W for the LT1084 (K, P), 30W for the
LT1084 (T) and 30W for the LT1085). Power dissipation is determined by
the input/output differential and the output current. Guaranteed maximum
power dissipation will not be available over the full input/output range.
Note 4: I
FULL LOAD
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.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
5
LT1083/LT1084/LT1085 Fixed
1083ffd
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 ≤ 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 FIXED 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 FIXED G06
–25 25 75 125
ΔI = 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
TJ = 150°C
TJ = 25°C
–55°C ≤ TJ ≤ 150°C
TJ = –55°C
0°C ≤ TJ ≤ 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
ΔI = 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
–55°C
I
FULL LOAD
GUARANTEED
150°C
LT1085 Short-Circuit Current
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
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 FIXED G03
0.05
0.10
–25 25 75 125
ΔI = 7.5A
LT1083 Dropout Voltage LT1083 Load Regulation
LT1083 Short-Circuit Current
TYPICAL PERFOR A CE CHARACTERISTICS
UW
6
LT1083/LT1084/LT1085 Fixed
1083ffd
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
FULLLOAD
LT1083/4/5-12 Ripple Rejection
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
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
FULLLOAD
)
0
RIPPLE REJECTION (dB)
100
90
80
70
60
50
40
30
20
10
0
0.4 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
LT1083/4/5-5 Ripple Rejection
vs CurrentLT1083/4/5-5 Ripple Rejection
OUTPUT CURRENT (0 TO I
FULLLOAD
)
0
RIPPLE REJECTION (dB)
100
90
80
70
60
50
40
30
20
10
0
0.4 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
VRIPPLE
≤ 0.5VP-P
VRIPPLE ≤ 3VP-P
(VIN – VOUT) ≥ 3V
(VIN – VOUT) ≥ VDROPOUT
IOUT = IFULLLOAD
TYPICAL PERFOR A CE CHARACTERISTICS
UW
7
LT1083/LT1084/LT1085 Fixed
1083ffd
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
monolithic IC regulators is current limit oscillations.
These can occur because in current limit the safe area
protection exhibits a negative impedance. The safe area
protection decreases the current limit as the input-to-
output voltage increases.That is the equivalent of having
a negitive resistance since increasing voltage causes
current to decrease. Negitive resistance during current
limit is not unique to the LT1083 series and has been
present on all power IC regulators. The value of negative
resistance is a function of how fast the current limit is
THERMAL
LIMIT
GND
VOUT
LT1083/4/5 BD
VIN
–
+
BLOCK DIAGRA
W
APPLICATIO S I FOR ATIO
WUUU
8
LT1083/LT1084/LT1085 Fixed
1083ffd
up into very heavy loads. During the start-up, as the input
voltage is rising, the input-to-output voltage differential
remains small allowing the regulator to supply large
output currents. With high input voltage a problem can
occur wherein removal of an output short will not allow the
output voltage to recover. Older regulators such as the
7800 series, also exhibited this phenomenon so it is not
unique to the LT1083.
The problem occurs with a heavy output load when the
input voltage is high and the output voltage is low, such as
immediately after a removal of a short. The load line for
such a load may intersect the output current curve at two
points. If this happens there are two stable output 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,
folded back as input-to-
output voltage increases. This
negative resistance can react with capacitors or inductors
on the input to cause oscillations during current limiting.
Depending on the value of series resistance, the overall
circuitry may end up unstable. Since this is a system
problem, it is not necessarily easy to solve; however it
does not cause any problems with the IC regulator and can
usually be ignored.
Protection Diodes
In normal operation the LT1083 family does not need any
protection diodes, The internal diode between the input
and the output pins of the LT1083 family can handle
microsecond surge currents of 50A to 100A. Even with
large output capacitances it is very difficult to get those
values of surge current in normal operation. Only with high
value output capacitors, such as 1000μF to 5000μF and
with the input pin instantaneously shorted to ground, can
damage occur. A crowbar circuit at the input of the LT1083
can generate those kinds of currents and a diode from
output-to-input is then recommended. Normal power sup-
ply cycling or even plugging and unplugging in the system
will not generate currents large enough to do any damage.
IN OUT
ADJ
VOUT
LT1083
D1
1N4002
(OPTIONAL)
VIN
1083/4/5 AI01
COUT
150μF
+
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
APPLICATIO S I FOR ATIO
WUUU
9
LT1083/LT1084/LT1085 Fixed
1083ffd
case-
to-heat sink interface, and heat sink resistance itself.
New thermal resistance specifications have been devel-
oped to more accurately reflect device temperature and
ensure safe operating temperatures. The data section for
these new regulators provides a separate thermal resis-
tance and maximum junction temperature for both the
Control Section
and the
Power Section
. Previous regula-
tors, with a single junction-to-case thermal resistance
specification, used an average of the two values provided
here and therefore could allow excessive junction tem-
peratures under certain conditions of ambient tempera-
ture 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 LT1083-5CP (TO-3P, 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 P 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 + 0.5°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.
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
+
APPLICATIO S I FOR ATIO
WUUU
TYPICAL APPLICATIO S
U
Paralleling Regulators
LT1083-5 OUTINVIN
VOUT = 5V
IOUT = 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
10
LT1083/LT1084/LT1085 Fixed
1083ffd
T Package
3-Lead Plastic TO-220
(LTC DWG # 05-08-1420)
K Package
2-Lead TO-3 Metal Can
(LTC DWG # 05-08-1310)
K2 (TO-3) 0801
.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)
.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)
7.5A Regulator
15V
15V
15V
110VAC
T1
TRIAD
F-269U
–
+
–
+
++
–
+
OUTIN LT1083-12 OUTIN
GND
C30B
C30B
34
20Ω
20Ω
12
L
1MH
T2
1N4003
1N4148
1N4003
1N914
C1
50,000μF100μF
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
TYPICAL APPLICATIO S
U
U
PACKAGE DESCRIPTIO
OBSOLETE PACKAGE
11
LT1083/LT1084/LT1085 Fixed
1083ffd
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.
U
PACKAGE DESCRIPTIO
P Package
3-Lead Plastic TO-3P (Similar to TO-247)
(LTC DWG # 05-08-1450)
.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
M Package
3-Lead Plastic DD Pak
(LTC DWG # 05-08-1460)
.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
12
LT1083/LT1084/LT1085 Fixed
1083ffd
© LINEAR TECHNOLOGY CORPORATION 1994
LT 1007 REV D • PRINTED IN USA
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
VIN > 11.5V
5VOUT
LT1085-5
LT1029
LT1083/4/5 TA07
10V
10μF100μF
++
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
VIN > 12V LT1085-5
LT1083/4/5 TA06
5V to 10V
10μF
*OPTIONAL IMPROVES RIPPLE REJECTION
10μF* 1k
100μF
+
+
+
TYPICAL APPLICATIO S
U
RELATED PARTS
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UltraFast and OPTI-LOOP are trademarks of Linear Technology Corporation.
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear.com
