ETC 508589A

LT1083/LT1084/LT1085
7.5A, 5A, 3A Low Dropout
Positive Adjustable Regulators
U
DESCRIPTIO
FEATURES
■
■
■
■
■
■
■
■
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
U
APPLICATIO S
■
■
■
■
High Efficiency Linear Regulators
Post Regulators for Switching Supplies
Constant Current Regulators
Battery Chargers
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 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 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 capacitor is required on these new devices. However, this is
included in most regulator designs.
DEVICE
OUTPUT CURRENT*
LT1083
LT1084
LT1085
7.5A
5.0A
3.0A
Unlike PNP regulators, where up to 10% of the output
current is wasted as quiescent current, the LT1083 quiescent current flows into the load, increasing efficiency.
, LTC and LT are registered trademarks of Linear Technology Corporation.
*For a 1.5A low dropout regulator see the LT1086 data sheet.
U
TYPICAL APPLICATIO
5V, 7.5A Regulator
IN
LT1083
ADJ
+
5V AT 7.5A
OUT
121Ω
1%
10µF
+
10µF*
TANTALUM
365Ω
1%
*REQUIRED FOR STABILITY
1083/4/5 ADJ TA01
INPUT/OUTPUT VOLTAGE DIFFERENTIAL (V)
VIN ≥ 6.5V
Dropout Voltage vs Output Current
2
1
0
0
IFULL LOAD
OUTPUT CURRENT
1083/4/5 ADJ TA02
1
LT1083/LT1084/LT1085
(Note 1)
“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
U
W
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
UU
W W
U
ABSOLUTE MAXIMUM RATINGS
PRECO DITIO I G
100% thermal shutdown functional test.
W
U
U
PACKAGE/ORDER INFORMATION
FRONT VIEW
TAB
IS
OUTPUT
3
VIN
2
VOUT
1
ADJ
T PACKAGE
3-LEAD PLASTIC TO-220
ORDER PART
NUMBER
TAB IS
OUTPUT
LT1084CT
LT1084IT
LT1085CT
LT1085IT
CASE IS
OUTPUT
1
VIN
2
VOUT
1
ADJ
LT1083CP
LT1084CP
θJA = 35°C/W
BOTTOM VIEW
2
3
P PACKAGE
3-LEAD PLASTIC TO-3P
θJA = 50°C/W
VIN
ORDER PART
NUMBER
FRONT VIEW
LT1083CK
LT1083MK
LT1084CK
LT1084MK
LT1085CK
LT1085MK
FRONT VIEW
TAB
IS
OUTPUT
3
VIN
2
VOUT
1
ADJ
LT1085CM
M PACKAGE
3-LEAD PLASTIC DD
ADJ
θJA = 30°C/W*
K PACKAGE
2-LEAD TO-3 METAL CAN
*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.
θJA = 35°C/W
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
PARAMETER
Reference Voltage
Line Regulation
CONDITIONS
IOUT = 10mA, TJ = 25°C,
(VIN – VOUT) = 3V
10mA ≤ IOUT ≤ IFULL LOAD
1.5V ≤ (VIN – VOUT) ≤ 25V (Notes 4, 6, 7)
ILOAD = 10mA, 1.5V ≤ (VIN – VOUT) ≤ 15V, TJ = 25°C (Notes 2, 3)
●
●
M Grade: 15V ≤ (VIN – VOUT) ≤ 35V (Notes 2, 3)
C, I Grades: 15V ≤ (VIN – VOUT) ≤ 30V (Notes 2, 3)
2
●
●
MIN
TYP
MAX
UNITS
1.238
1.250
1.262
V
1.225
1.250
0.015
0.035
0.05
0.05
1.270
0.2
0.2
0.5
0.5
V
%
%
%
%
LT1083/LT1084/LT1085
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
PARAMETER
Load Regulation
CONDITIONS
(VIN – VOUT) = 3V
10mA ≤ IOUT ≤ IFULL LOAD
TJ = 25°C (Notes 2, 3, 4, 6)
MIN
●
Dropout Voltage
Current Limit
LT1083
LT1084
LT1085
Minimum Load Current
Thermal Regulation
LT1083
LT1084
LT1085
Ripple Rejection
Adjust Pin Current
∆VREF = 1%, IOUT = IFULLLOAD (Notes 5, 6, 8)
●
(VIN – VOUT) = 5V
(VIN – VOUT) = 25V
(VIN – VOUT) = 5V
(VIN – VOUT) = 25V
(VIN – VOUT) = 5V
(VIN – VOUT) = 25V
(VIN – VOUT) = 25V
TA = 25°C, 30ms Pulse
●
●
●
●
●
●
8.0
0.4
5.5
0.3
3.2
0.2
●
f = 120Hz, CADJ = 25µF, COUT = 25µF Tantalum
IOUT = IFULL LOAD, (VIN – VOUT) = 3V (Notes 6, 7, 8)
TJ = 25°C
●
60
TYP
MAX
UNITS
0.1
0.2
1.3
0.3
0.4
1.5
%
%
V
9.5
1.0
6.5
0.6
4.0
0.5
5
10
A
A
A
A
A
A
mA
0.002
0.003
0.004
0.010
0.015
0.020
%/W
%/W
%/W
75
55
120
●
Adjust Pin Current Change
Temperature Stability
Long Term Stability
RMS Output Noise (% of VOUT)
Thermal Resistance Junction-to-Case
LT1083
LT1084
LT1085
10mA ≤ IOUT ≤ IFULL LOAD
1.5V ≤ (VIN – VOUT) ≤ 25V (Note 6)
●
●
TA = 125°C, 1000 Hrs
TA = 25°C
10Hz = ≤ f ≤ 10kHz
Control Circuitry/Power Transistor
K Package
P Package
K Package
P Package
T Package
K Package
M, T Packages
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.
0.2
0.5
0.3
5
1
0.003
dB
µA
µA
µA
%
%
%
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
Note 4: IFULL LOAD is defined in the current limit curves. The IFULLLOAD
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 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.
3
LT1083/LT1084/LT1085
U W
TYPICAL PERFORMANCE CHARACTERISTICS
LT1083
Dropout Voltage
LT1083
Short-Circut Current
12
MINIMUM INPUT/OUTPUT DIFFERENTIAL (V)
2
0.10
INDICATES GUARANTEED TEST POINT
SHORT-CIRCUIT CURRENT (A)
0°C ≤ TJ ≤ 125°C
1
TJ = 150°C
TJ = 25°C
TJ = –55°C
OUTPUT VOLTAGE DEVIATION (%)
∆I = 7.5A
–40°C ≤ TJ ≤ 150°C
25°C
10
150°C
8
6
–55°C
4
2
IFULL LOAD
GUARANTEED
0
0
1
2
3 4 5 6 7 8
OUTPUT CURRENT (A)
9
0
10
20
30
15
25
5
10
INPUT/OUTPUT DIFFERENTIAL (V)
LT1084
Dropout Voltage
INDICATES GUARANTEED TEST POINT
SHORT-CIRCUIT CURRENT (A)
0°C ≤ TJ ≤ 125°C
1
TJ = –55°C
TJ = 25°C
0
25 50 75 100 125 150
TEMPERATURE (°C)
LT1083/4/5 ADJ G03
LT1084
Load Regulation
∆I = 5A
8
7
150°C
25°C
6
–55°C
5
4
3
2
IFULL LOAD
GUARANTEED
0
0
5
–0.15
0.10
1
3
4
2
OUTPUT CURRENT (A)
–0.10
9
–55°C ≤ TJ ≤ 150°C
1
–0.05
LT1084
Short-Circut Current
10
2
0
0
LT1083/4/5 ADJ G02
LT1083/4/5 ADJ G01
TJ = 150°C
0.05
–0.20
–50 –25
35
OUTPUT VOLTAGE DEVIATION (%)
0
MINIMUN INPUT/OUTPUT DIFFERENTIAL (V)
LT1083
Load Regulation
0
6
20
15
10
25
30
5
INPUT/OUTPUT DIFFERENTIAL (V)
0.05
0
–0.05
–0.10
–0.15
–0.20
–50 –25
35
0
25 50 75 100 125 150
TEMPERATURE (°C)
LT1083/4/5 ADJ G05
LT1083/4/5 ADJ G06
LT1083/4/5 ADJ G04
LT1085
Short-Circut Current
LT1085
Load Regulation
6
2
0.10
INDICATES GUARANTEED TEST POINT
–55°C ≤ TJ ≤ 150°C
0°C ≤ TJ ≤ 125°C
1
TJ = –55°C
TJ = 25°C
TJ = 150°C
5
25°C
4
150°C
3
–55°C
2
IFULL LOAD
GUARANTEED
1
0
0
0
3
2
1
OUTPUT CURRENT (A)
4
LT1083/4/5 ADJ G07
4
OUTPUT VOLTAGE DEVIATION (%)
∆I = 3A
SHORT-CIRCUIT CURRENT (A)
MINIMUM INPUT/OUTPUT DIFFERENTIAL (V)
LT1085
Dropout Voltage
0
20
30
15
25
5
10
INPUT/OUTPUT DIFFERENTIAL (V)
35
LT1083/4/5 ADJ G08
0.05
0
–0.05
–0.10
–0.15
–0.20
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
LT1083/4/5 ADJ G09
LT1083/LT1084/LT1085
U W
TYPICAL PERFORMANCE CHARACTERISTICS
Minimum Operating Current
Temperature Stability
100
9
7
6
5
TJ = 150°C
4
TJ = 25°C
3
ADJUST PIN CURRENT (µA)
90
8
1.26
1.25
1.24
2
TJ = –55°C
0
20
15
10
25
30
5
INPUT/OUTPUT DIFFERENTIAL (V)
35
0
40
30
CADJ = 200µF AT FREQUENCIES < 60Hz
CADJ = 25µF AT FREQUENCIES > 60Hz
IOUT = 7A
20
10
100
1k
10k
FREQUENCY (Hz)
60
70
50
40
VOUT = 5V
CADJ = 25µF
COUT = 25µF
10
7
6
4
3
2
5
OUTPUT CURRENT (A)
1
LT1083/4/5 ADJ G15
LT1084
Maximum Power Dissipation*
60
100
30
CADJ = 200µF AT FREQUENCIES < 60Hz
CADJ = 25µF AT FREQUENCIES > 60Hz
IOUT = 5A
10
10
100
1k
10k
FREQUENCY (Hz)
60
1083/4/5 ADJ G16
40
50
40
30
LT1084CT
LT1084CP
20
30
VOUT = 5V
CADJ = 25µF
COUT = 25µF
10
100k
LT1084MK
fR = 20kHz
VRIPPLE ≤ 0.5VP-P
70
20
0
50
POWER (W)
RIPPLE REJECTION (dB)
40
20
fR = 120Hz
VRIPPLE ≤ 3VP-P
90
80
(VIN – VOUT) ≥ VDROPOUT
50
LT1083CK
50 60 70 80 90 100 110 120 130 140 150
CASE TEMPERATURE (°C)
* AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE
8
LT1084
Ripple Rejection vs Current
(VIN – VOUT) ≥ 3V
LT1083CP
10
1083/4/5 ADJ G14
VRIPPLE ≤ 3VP-P VRIPPLE ≤ 0.5VP-P
60
40
0
0
100
70
50
20
0
100k
LT1083MK
60
30
30
LT1084
Ripple Rejection
80
25 50 75 100 125 150
TEMPERATURE (°C)
80
1083/4/5 ADJ G13
90
0
90
fR = 20kHz
VRIPPLE ≤ 0.5VP-P
70
20
0
10
20
100
80
(VIN – VOUT) ≥ VDROPOUT
50
30
LT1083
Maximum Power Dissipation*
fR = 120Hz
VRIPPLE ≤ 3VP-P
90
RIPPLE REJECTION (dB)
RIPPLE REJECTION (dB)
60
40
LT1083/4/5 ADJ G12
100
VRIPPLE
≤ 0.5VP-P
(VIN – VOUT) ≥ 3V
70
50
LT1083
Ripple Rejection vs Current
VRIPPLE ≤ 3VP-P
80
60
LT1083/4/5 ADJ G11
LT1083
Ripple Rejection
90
70
0
–50 –25
25 50 75 100 125 150
TEMPERATURE (°C)
LT1083/4/5 ADJ G10
100
80
10
1.23
–50 –25
POWER (W)
1
0
RIPPLE REJECTION (dB)
Adjust Pin Current
1.27
REFERENCE VOLTAGE (V)
MINIMUM OPERATING CURRENT (mA)
10
10
LT1084CK
0
0
0
1
4
3
2
OUTPUT CURRENT (A)
5
1083/4/5 ADJ G17
50 60 70 80 90 100 110 120 130 140 150
CASE TEMPERATURE (°C)
* AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE
LT1083/4/5 ADJ G18
5
LT1083/LT1084/LT1085
U W
TYPICAL PERFORMANCE CHARACTERISTICS
LT1085
Ripple Rejection
90
80
70
60
(VIN – VOUT) ≥ VDROPOUT
50
40
30
CADJ = 200µF AT FREQUENCIES < 60Hz
CADJ = 25µF AT FREQUENCIES > 60Hz
IOUT = 3A
100
1k
10k
FREQUENCY (Hz)
50
40
10
VOUT = 5V
CADJ = 25µF
COUT = 25µF
LT1085CK
0
0
0
0.5
2.5
2.0
1.0
1.5
OUTPUT CURRENT (A)
1083/4/5 ADJ G19
0.4
OUTPUT VOLTAGE
DEVIATION (V)
0.4
CADJ = 1µF
0
CIN = 1µF
COUT = 10µF TANTALUM
LOAD CURRENT (A)
–0.4
8
VOUT =10V
VIN =13V
PRELOAD=100mA
6
4
2
0
0
50
TIME (µs)
100
0.3
CADJ = 1µF
0.2
0
–0.2
CIN = 1µF
COUT = 10µF TANTALUM
–0.4
6
VOUT = 10V
VIN = 13V
PRELOAD=100mA
4
2
0
0
50
TIME (µs)
OUTPUT VOLTAGE
DEVIATION (V)
CADJ = 1µF
50
0
–50
–100
VOUT = 10V
IIN = 0.2A
CIN = 1µF TANTALUM
COUT = 10µF TANTALUM
14
13
12
0
100
TIME (µs)
–0.1
200
1083/4/5 ADJ G25
CIN = 1µF
COUT = 10µF TANTALUM
–0.2
–0.3
3
VOUT = 10V
VIN = 13V
PRELOAD=100mA
2
1
0
0
50
TIME (µs)
100
LT1085
Line Transient Response
60
CADJ = 0
40
CADJ = 1µF
20
0
–20
–40
VOUT = 10V
IIN = 0.2A
CIN = 1µF TANTALUM
COUT = 10µF TANTALUM
–60
INPUT
DEVIATION (V)
–150
0
1083/4/5 ADJ G24
60
CADJ = 0
100
CADJ = 1µF
0.1
LT1084
Line Transient Response
150
OUTPUT VOLTAGE
DEVIATION (mV)
100
CADJ = 0
0.2
1083/4/5 ADJ G23
LT1083
Line Transient Response
INPUT
DEVIATION (V)
LT1085
Load Transient Response
CADJ = 0
1083/4/5 ADJ G22
6
LT1083/4/5 ADJ G21
–0.6
LOAD CURRENT (A)
OUTPUT VOLTAGE
DEVIATION (V)
0.6
–0.2
50 60 70 80 90 100 110 120 130 140 150
CASE TEMPERATURE (°C)
* AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE
LT1084
Load Transient Response
0.6
0.2
3.0
1083/4/5 ADJ G20
LT1083
Load Transient Response
CADJ = 0
20
LT1085CT
10
100k
LT1085MK
30
30
20
0
10
fR = 20kHz
VRIPPLE ≤ 0.5VP-P
OUTPUT VOLTAGE
DEVIATION (mV)
10
60
14
13
12
0
100
TIME (µs)
CADJ = 0
40
CADJ = 1µF
20
0
–20
–40
VOUT = 10V
IIN = 0.2A
CIN = 1µF TANTALUM
COUT = 10µF TANTALUM
–60
INPUT
DEVIATION (V)
20
40
fR = 120Hz
VRIPPLE ≤ 3VP-P
70
POWER (W)
(VIN – VOUT) ≥ 3V
RIPPLE REJECTION (dB)
RIPPLE REJECTION (dB)
80
50
100
VRIPPLE
≤ 0.5VP-P
OUTPUT VOLTAGE
DEVIATION (V)
VRIPPLE ≤ 3VP-P
90
LT1085
Maximum Power Dissipation*
LOAD CURRENT (A)
100
LT1085
Ripple Rejection vs Current
200
1083/4/5 ADJ G26
14
13
12
0
100
TIME (µs)
200
1083/4/5 ADJ G27
LT1083/LT1084/LT1085
W
BLOCK DIAGRAM
VIN
+
–
THERMAL
LIMIT
VOUT
1083/4/5 ADJ BD
VADJ
U
W
U
U
APPLICATIONS INFORMATION
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 threeterminal adjustable devices, offer lower dropout voltage
and more precise reference tolerance. Further, the reference stability with temperature is improved over older
types of regulators. The only circuit difference between
using the LT1083 family and older regulators is that 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 characteristics are available. These capacitors differ in capacitor
tolerance (sometimes ranging up to ±100%), equivalent
series resistance, and capacitance temperature coefficient. The 150µF or 22µF values given will ensure stability.
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
10µF
10µF
OUTPUT
10µF Tantalum, 50µF Aluminum
22µF Tantalum, 150µF Aluminum
ADJUSTMENT
None
20µF
7
LT1083/LT1084/LT1085
U
W
U
U
APPLICATIONS INFORMATION
Normally, capacitor values on the order of 100µF are used
in the output of many regulators to ensure good transient
response with heavy load current changes. Output capacitance can be increased without limit and larger values of
output capacitor further improve stability and transient
response of the LT1083 regulators.
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.
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 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 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.
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, exceeding the maximum input to output voltage differential
causes the internal transistors to break down and none of
the protection circuitry is functional.
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 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
currents of 50A to 100A. Even with large output capacitances, 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
8
D1
1N4002
(OPTIONAL)
VIN
IN
LT1083
OUT
ADJ
+
R1
CADJ
10µF
+
VOUT
COUT
150µF
R2
1083/4/5 ADJ F00
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.
LT1083/LT1084/LT1085
U
W
U
U
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 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.
IN
VIN
OUT
LT1083
ADJ
VOUT
VREF
R1
IADJ
50µA
(
VOUT = VREF 1 + R2
R1
)
R2
+ IADJ R2
1083/4/5 ADJ F01
Figure 1. Basic Adjustable Regulator
Ripple Rejection
Load Regulation
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.
Because the LT1083 is a three-terminal device, it is not
possible 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 specification
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 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 between the regulator and the load would be:
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 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 IADJ is very small and constant when compared
with the current through R1, it represents a small error and
can usually be ignored.
 R2 + R1
RP × 
 , RP = Parasitic Line Resistance
 R1 
RP
PARASITIC
LINE RESISTANCE
VIN
IN
LT1083
OUT
ADJ
R1*
RL
R2*
*CONNECT R1 TO CASE
CONNECT R2 TO LOAD
1083/4/5 ADJ F02
Figure 2. Connections for Best Load Regulation
9
LT1083/LT1084/LT1085
U
W
U
U
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
important to keep the positive lead between regulator and
load as short as possible and use large wire or PC board
traces.
compound at the case-to-heat sink interface is strongly
recommended. If the case of the device must be electrically 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.
Thermal Considerations
For example, using an LT1083CK (TO-3, Commercial) and
assuming:
The LT1083 series of regulators have internal power and
thermal limiting circuitry designed to protect the device
under overload conditions. For continuous normal load
conditions however, maximum junction temperature ratings must not be exceeded. It is important to give careful
consideration to all sources of thermal resistance from
junction to ambient. This includes junction-to-case, caseto-heat sink interface, and heat sink resistance itself. New
thermal resistance specifications have been developed to
more accurately reflect device temperature and ensure
safe operating temperatures. The data section for these
new regulators provides a separate thermal resistance and
maximum junction temperature for both the Control Section 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
10
VIN (max continuous) = 9V, VOUT = 5V, IOUT = 6A,
TA = 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:
PD = (VIN – VOUT )(IOUT) = 24W
Junction temperature will be equal to:
TJ = TA + PD (θHEAT SINK + θCASE-TO-HEAT SINK + θJC)
For the Control Section:
TJ = 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:
TJ = 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
maximum rating for the respective sections, ensuring
reliable operation.
LT1083/LT1084/LT1085
U
TYPICAL APPLICATIONS
7.5A Variable Regulator
T1
TRIAD
F-269U
L
1MH
C30B
IN
20Ω
3
110VAC
20Ω
T2
1
+
750Ω*
100µF
50,000µF
2
1N914
2k
OUTPUT
ADJUST
1N4003
1µF
16k*
560Ω
15V
82k
15k
–15V
8
2
+
3
10k
LT1004-1.2
16k*
200k
11k*
7
–15V
0.1µF
–
1
1N4148
NC
15V
100pF
2N3904
8
–15V
4
7
2.7k
4
LT1011
* 1% FILM RESISTOR
L: DALE TO-5 TYPE
T2: STANCOR 11Z-2003
1.5k
0V TO 35V
OA TO 7.5A
LT1004-1.2
C30B
1N4003
OUT
ADJ
+ C1
1N4003
LT1083
–
3
1
8
LT1011
+
10k
2
6
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
3
–
2
LM301A
1
15K
+
7
15V
4
–15V
11k*
15V
1µF
LT1083/4/5 ADJ TA05
11
LT1083/LT1084/LT1085
U
TYPICAL APPLICATIONS
Paralleling Regulators
VIN
IN
LT1083
2 FEET #18 WIRE*
OUT
( )
ADJ
VOUT = 1.25V 1 + R2
R1
IOUT = 0A TO 15A
0.015Ω
IN
LT1083
OUT
*THE #18 WIRE ACTS
AS BALLAST RESISTANCE
INSURING CURRENT SHARING
BETWEEN BOTH DEVICES
ADJ
R1
120Ω
LT1083/4/5 ADJ TA03
R2
Improving Ripple Rejection
VIN
IN
LT1083
R1
121Ω
1%
ADJ
+
VOUT
5V
OUT
10µF
+
150µF
R2
365Ω
1%
+
C1
25µF*
*C1 IMPROVES RIPPLE REJECTION.
XC SHOULD BE < R1 AT RIPPLE FREQUENCY
1083/4/5 ADJ TA04
Remote Sensing
RP
(MAX DROP 300mV)
VIN
IN
LT1083
+
ADJ
10µF
VIN
100µF
25Ω
+
VOUT
5V
OUT
121Ω
7
6
–
LM301A
1
+
3
100pF
1k
RL
8
4
365Ω
2
5µF
+
25Ω
RETURN
RETURN
1083/4/5 ADJ TA07
12
LT1083/LT1084/LT1085
U
TYPICAL APPLICATIONS
High Efficiency Regulator with Switching Preregulator
1mH
VIN
28V
IN
+
LT1083
ADJ
10,000µF
MR1122
VOUT
OUT
240Ω
470Ω
10k
1N914
28V
1k
1M
2k
4N28
10k
+
1083/4/5 ADJ TA06
LT1011
10k
–
28V
1N914
1.2V to 15V Adjustable Regulator
VIN
IN
LT1083
R1
90.9Ω
ADJ
+
C1*
10µF
VOUT†
OUT
+
C2
100µF
R2
1k
*NEEDED IF DEVICE IS FAR FROM FILTER CAPACITORS
R2
OUT = 1.25V 1 +
R1
(
†V
)
1083/4/5 ADJ TA08
5V Regulator with Shutdown*
VIN
IN
LT1083
ADJ
+
VOUT
5V
OUT
121Ω
1%
+
10µF
100µF
1k
2N3904
TTL
365Ω
1%
1k
1083/4/5 ADJ TA09
*OUTPUT SHUTS DOWN TO 1.3V
13
LT1083/LT1084/LT1085
U
PACKAGE DESCRIPTION
Dimension in inches (millimeters) unless otherwise noted.
K Package
2-Lead TO-3 Metal Can
(LTC DWG # 05-08-1310)
0.760 – 0.775
(19.30 – 19.69)
0.320 – 0.350
(8.13 – 8.89)
0.060 – 0.135
(1.524 – 3.429)
0.420 – 0.480
(10.67 – 12.19)
0.038 – 0.043
(0.965 – 1.09)
1.177 – 1.197
(29.90 – 30.40)
0.655 – 0.675
(16.64 – 17.15)
0.210 – 0.220
(5.33 – 5.59)
0.151 – 0.161
(3.86 – 4.09)
DIA, 2PLCS
0.167 – 0.177
(4.24 – 4.49)
R
0.425 – 0.435
(10.80 – 11.05)
0.067 – 0.077
(1.70 – 1.96)
0.490 – 0.510
(12.45 – 12.95)
R
K2 (TO-3) 1098
M Package
3-Lead Plastic DD Pak
(LTC DWG # 05-08-1460)
0.256
(6.502)
0.060
(1.524)
0.060
(1.524)
TYP
0.390 – 0.415
(9.906 – 10.541)
0.165 – 0.180
(4.191 – 4.572)
15° TYP
0.060
(1.524)
0.183
(4.648)
0.059
(1.499)
TYP
0.330 – 0.370
(8.382 – 9.398)
BOTTOM VIEW OF DD PAK
HATCHED AREA IS SOLDER PLATED
COPPER HEAT SINK
14
(
+0.008
0.004 –0.004
+0.203
0.102 –0.102
)
0.095 – 0.115
(2.413 – 2.921)
0.075
(1.905)
0.300
(7.620)
0.045 – 0.055
(1.143 – 1.397)
(
+0.012
0.143 – 0.020
+0.305
3.632 –0.508
)
0.090 – 0.110
(2.286 – 2.794)
0.050
(1.270)
BSC
0.013 – 0.023
(0.330 – 0.584)
0.050 ± 0.012
(1.270 ± 0.305)
M (DD3) 1098
LT1083/LT1084/LT1085
U
PACKAGE DESCRIPTION
Dimension in inches (millimeters) unless otherwise noted.
P Package
3-Lead Plastic TO-3P (Similar to TO-247)
(LTC DWG # 05-08-1450)
0.560
(14.224)
0.325
(8.255)
0.187 – 0.207
(4.75 – 5.26)
0.620 – 0.64O
(15.75 – 16.26)
0.275
(6.985)
0.580
(14.732)
0.830 – 0.870
(21.08 – 22.10)
0.700
(17.780)
0.060 – 0.080
(1.52 – 2.03)
0.170 – 0.2OO
(4.32 – 5.08)
EJECTOR PIN MARKS
0.105 – 0.125
(2.67 – 3.18)
DIA
0.580 – 0.6OO
(14.73 – 15.24)
0.098
(2.489)
0.124
(3.149)
MOUNTING HOLE
18° – 22°
0.115 – 0.145
(2.92 – 3.68)
DIA
3° – 7°
0.170
(4.32)
MAX
0.780 – 0.800
(19.81 – 20.32)
0.042 – 0.052
(1.07 – 1.32)
BOTTOM VIEW OF TO-3P
HATCHED AREA IS SOLDER PLATED
COPPER HEAT SINK
0.215
(5.46)
BSC
0.074 – 0.084
(1.88 – 2.13)
0.087 – 0.102
(2.21 – 2.59)
0.020 – 0.040
(0.51 – 1.02)
0.113 – 0.123
(2.87 – 3.12)
P3 0996
T Package
3-Lead Plastic TO-220
(LTC DWG # 05-08-1420)
0.147 – 0.155
(3.734 – 3.937)
DIA
0.390 – 0.415
(9.906 – 10.541)
0.165 – 0.180
(4.191 – 4.572)
0.045 – 0.055
(1.143 – 1.397)
0.230 – 0.270
(5.842 – 6.858)
0.460 – 0.500
(11.684 – 12.700)
0.570 – 0.620
(14.478 – 15.748)
0.330 – 0.370
(8.382 – 9.398)
0.980 – 1.070
(24.892 – 27.178)
0.520 – 0.570
(13.208 – 14.478)
0.100
(2.540)
BSC
0.218 – 0.252
(5.537 – 6.401)
0.013 – 0.023
(0.330 – 0.584)
0.028 – 0.038
(0.711 – 0.965)
0.050
(1.270)
TYP
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
0.095 – 0.115
(2.413 – 2.921)
T3 (TO-220) 1098
15
LT1083/LT1084/LT1085
U
TYPICAL APPLICATIONS
Automatic Light Control
VIN
IN
LT1083
OUT
ADJ
+
1.2k
100µF
10µF
1083/4/5 ADJ TA10
Protected High Current Lamp Driver
12V
5A
OUT
LT1083
IN
15V
ADJ
TTL OR
CMOS
1083/4/5 ADJ TA11
10k
RELATED PARTS
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% 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.
16
Linear Technology Corporation
108345fd LT/TP 0200 2K REV D • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com
 LINEAR TECHNOLOGY CORPORATION 1994