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PDF LT1085 Data sheet ( Hoja de datos )
| Número de pieza | LT1085 | |
| Descripción | Low Dropout Positive Adjustable Regulators | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LT1085 (archivo pdf) en la parte inferior de esta página. Total 22 Páginas | ||
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LT1083/LT1084/LT1085
7.5A, 5A, 3A Low Dropout
Positive Adjustable Regulators
Features
nn 3-Terminal Adjustable
nn Output Current of 3A, 5A or 7.5A
nn Operates Down to 1V Dropout
nn Guaranteed Dropout Voltage at Multiple Current Levels
nn Line Regulation: 0.015%
nn Load Regulation: 0.1%
nn 100% Thermal Limit Functional Test
nn Fixed Versions Available
nn Available in 3-Lead Plastic TO-220 and DD Packages
Applications
nn High Efficiency Linear Regulators
nn Post Regulators for Switching Supplies
nn Constant Current Regulators
nn 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.
Description
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 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 flows into the load, increasing efficiency.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
UltraFast and ThinSOT are trademarks of Linear Technology Corporation. All other trademarks
are the property of their respective owners.
Typical Application
5V, 7.5A Regulator
VIN ≥ 6.5V
+
IN
10µF
LT1083 OUT
ADJ
*REQUIRED FOR STABILITY
121Ω
1% +
365Ω
1%
5V AT 7.5A
10µF*
TANTALUM
1083/4/5 ADJ TA01
Dropout Voltage vs Output Current
2
1
0
0 IFULL LOAD
OUTPUT CURRENT
1083/4/5 ADJ TA02
For more information www.linear.com/LT1083
108345fh
1
1 page  
LT1083/LT1084/LT1085
Electrical Characteristics The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
PARAMETER
CONDITIONS
MIN TYP MAX
Reference Voltage
Line Regulation
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)
1.238
l 1.225
l
1.250
1.250
0.015
0.035
1.262
1.270
0.2
0.2
Load Regulation
M-Grade: 15V ≤ (VIN – VOUT) ≤ 35V (Notes 2, 3)
l 0.05 0.5
C-, I-Grades: 15V ≤ (VIN – VOUT) ≤ 30V (Notes 2, 3)
l 0.05 0.5
(VIN – VOUT) = 3V, 10mA ≤ IOUT ≤ IFULL_LOAD, TJ = 25°C
(Notes 2, 3, 4, 6)
l
0.1 0.3
0.2 0.4
Dropout Voltage
Current Limit
LT1083
LT1084
LT1085
Minimum Load Current
Thermal Regulation
LT1083
LT1084
LT1085
∆VREF = 1%, IOUT = IFULL_LOAD (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
l
l 8.0
l 0.4
l 5.5
l 0.3
l
l
3.2
0.2
l
1.3 1.5
9.5
1.0
6.5
0.6
4.0
0.5
5 10
0.002
0.003
0.004
0.010
0.015
0.020
Ripple Rejection
Adjust Pin Current
f = 120Hz, CADJ = 25µF, COUT = 25µF Tantalum
IOUT = IFULL_LOAD, (VIN – VOUT) = 3V (Notes 6, 7, 8)
TJ = 25°C
l 60
l
75
55
120
Adjust Pin Current Change
Temperature Stability
10mA ≤ IOUT ≤ IFULL_LOAD, 1.5V ≤ (VIN – VOUT) ≤ 25V (Note 6)
l
l
0.2 5
0.5
Long-Term Stability
RMS Output Noise (% of VOUT)
Thermal Resistance Junction-to-Case
LT1083
LT1084
LT1085
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 Package
0.3
0.003
1
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
UNITS
V
V
%
%
%
%
%
%
V
A
A
A
A
A
A
mA
%/W
%/W
%/W
dB
µA
µA
µA
%
%
%
°C/W
°C/W
°C/W
°C/W
°C/W
°C/W
°C/W
For more information www.linear.com/LT1083
108345fh
5
5 Page 
LT1083/LT1084/LT1085
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 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 resis-
tance can react with capacitors or inductors on the input
to cause oscillation during current limiting. Depending
on the value of series resistance, the overall circuitry may
end up unstable. Since this is a system problem, it is not
necessarily easy to solve; however, it does not cause any
problems with the IC regulator and can usually be ignored.
Protection Diodes
In normal operation, the LT1083 family does not need
any protection diodes. Older adjustable regulators 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 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 input
pin instantaneously shorted to ground, can damage occur.
A crowbar circuit at the input of the LT1083 can generate
those kinds of currents, and a diode from output to input is
then recommended. Normal power supply cycling or even
plugging and unplugging in the system will not generate
current large enough to do any damage.
The adjustment pin can be driven on a transient basis
± 25V, with respect to the output without any device 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.
D1
1N4002
(OPTIONAL)
VIN
IN LT1083 OUT
ADJ
R1
+
VOUT
COUT
150µF
+ CADJ
10µF
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.
For more information www.linear.com/LT1083
108345fh
11
11 Page | ||
| Páginas | Total 22 Páginas | |
| PDF Descargar | [ Datasheet LT1085.PDF ] | |
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