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PDF LT1521CS8-3.3 Data sheet ( Hoja de datos )
| Número de pieza | LT1521CS8-3.3 | |
| Descripción | 300mA Low Dropout Regulators with Micropower Quiescent Current and Shutdown | |
| Fabricantes | Linear Technology | |
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LT1521/LT1521-3
LT1521-3.3/LT1521-5
300mA Low Dropout
Regulators with Micropower
Quiescent Current and Shutdown
FEATURES
s Dropout Voltage: 0.5V
s Output Current: 300mA
s Quiescent Current: 12µA
s No Protection Diodes Needed
s Adjustable Output from 3.8V to 20V
s Fixed Output Voltages: 3V, 3.3V, 5V
s Controlled Quiescent Current in Dropout
s Shutdown IQ = 6µA
s Reverse Battery Protection
s No Reverse Current
s Thermal Limiting
U
APPLICATIONS
s Low Current Regulator
s Regulator for Battery-Powered Systems
s Post Regulator for Switching Supplies
DESCRIPTION
The LT®1521/LT1521-3/LT1521-3.3/LT1521-5 are low
dropout regulators with micropower quiescent current
and shutdown. These devices are capable of supplying
300mA of output current with a dropout voltage of 0.5V.
Designed for use in battery-powered systems, the low
quiescent current, 12µA operating and 6µA in
shutdown, makes them an ideal choice. The quiescent
current is well controlled; it does not rise in dropout as it
does with many other low dropout PNP regulators.
Other features of the LT1521/LT1521-3/LT1521-3.3/
LT1521-5 include the ability to operate with very small
output capacitors. They are stable with only 1.5µF on the
output while most older devices require between 10µF and
100µF for stability. Small ceramic capacitors can be used,
enhancing manufacturability. Also, the input may be con-
nected to voltages lower than the output voltage, including
negative voltages, without reverse current flow from out-
put to input. This makes the LT1521 series ideal for backup
power situations where the output is held high and the
input is low or reversed. Under these conditions only 5µA
will flow from the output pin to ground.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
5V Battery-Powered Supply with Shutdown
8 IN
OUT 1
6V 1µF
LT1521-5
5 SHDN
SENSE 2
GND
3
5V
300mA
+
1.5µF
VSHDN (PIN 5) OUTPUT
<0.25
OFF
>2.80
ON
NC ON
LT1521 • TA01
Dropout Voltage
0.6
0.5
0.4
0.3
0.2
0.1
0
0 50 100 150 200 250 300
OUTPUT CURRENT (mA)
LT1521 • TA02
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LT1521/LT1521-3
LT1521-3.3/LT1521-5
LT1521-3
Output Voltage
3.08
3.06
3.04
3.02
3.00
2.98
2.96
2.94
2.92
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
LT1521 • TPC04
LT1521
Adjust Pin Voltage
3.83
ILOAD = 1mA
3.81
3.79
3.77
3.75
3.73
3.71
3.69
3.67
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
LT1521 • TPC07
LT1521-5
Quiescent Current
50
45
TJ = 25°C
RL = ∞
40
35
30
25
20
15 VSHDN = OPEN
10
5 VSHDN = 0V
0
0 1 2 3 4 5 6 7 8 9 10
INPUT VOLTAGE (V)
LT1521 • TPC10
LT1521-3.3
Output Voltage
3.38
3.36 IOUT = 1mA
3.34
3.32
3.30
3.28
3.26
3.24
3.22
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
LT1521 • TPC05
LT1521-3
Quiescent Current
50
45
TJ = 25°C
RL = ∞
40
35
30
25
20
15 VSHDN = OPEN
10
5 VSHDN = 0V
0
0 1 2 3 4 5 6 7 8 9 10
INPUT VOLTAGE (V)
LT1521 • TPC08
LT1521
Quiescent Current
50
45
TJ = 25°C
RL = ∞
40
35
30
25
20
15
VSHDN = OPEN
10
5 VSHDN = 0V
0
0 1 2 3 4 5 6 7 8 9 10
INPUT VOLTAGE (V)
LT1521 • TPC11
LT1521-5
Output Voltage
5.08
5.06
5.04
5.02
5.00
4.98
4.96
4.94
4.92
–50 –25
0 25 50 75 100 125
TEMPERATURE (°C)
LT1521 • TPC06
LT1521-3.3
Quiescent Current
50
45
40
TJ = 25°C
RL = ∞
35
30
25
20
15
10
5
0
0 1 2 3 4 5 6 7 8 9 10
INPUT VOLTAGE (V)
LT1521 • TPC09
LT1521-3
Ground Pin Current
1000
900
800
700
TJ = 25°C
*FOR VOUT = 3V
RLOAD = 60Ω
ILOAD = 50mA*
600
500
RLOAD = 120Ω
ILOAD = 25mA*
400
RLOAD = 300Ω
300 ILOAD = 10mA*
200
RLOAD = 3k
100 ILOAD = 1mA*
0
0 1 2 3 4 5 6 7 8 9 10
INPUT VOLTAGE (V)
LT1521 • TPC12
5
5 Page 
LT1521/LT1521-3
LT1521-3.3/LT1521-5
APPLICATIONS INFORMATION
Table 3. SOT-223 Package
(Thermal Resistance Junction-to-Tab 20°C/W)
COPPER AREA
THERMAL RESISTANCE
TOPSIDE* BACKSIDE BOARD AREA (JUNCTION-TO-AMBIENT)
2500mm2 2500mm2 2500mm2
50°C/W
1000mm2 2500mm2 2500mm2
50°C/W
225mm2 2500mm2 2500mm2
58°C/W
100mm2 2500mm2 2500mm2
64°C/W
1000mm2 1000mm2 1000mm2
57°C/W
1000mm2
0
1000mm2
60°C/W
* Tab of device attached to topside copper.
Calculating Junction Temperature
Example: Given an output voltage of 3.3V, an input voltage
range of 4.5V to 7V, an output current range of 0mA to
150mA and a maximum ambient temperature of 50°C,
what will the maximum junction temperature be?
The power dissipated by the device will be equal to:
IOUT(MAX)(VIN(MAX) – VOUT) + IGND(VIN(MAX))
Where,
IOUT(MAX) = 150mA
VIN(MAX) = 7V
IGND at (IOUT = 150mA, VIN = 7V) = 2.1mA
So,
P = 150mA(7V – 3.3V) + (2.1mA)(7V) = 0.57W
If we use a SOT-223 package, then the thermal resistance
will be in the range of 50°C/W to 65°C/W depending on the
copper area. So the junction temperature rise above
ambient will be approximately equal to:
0.57W(60°C/W) = 34.2°C
The maximum junction temperature will then be equal to the
maximum junction temperature rise above ambient plus the
maximum ambient temperature or:
TJMAX = 50°C + 34.2°C = 84.2°C
Output Capacitance and Transient Performance
The LT1521 is designed to be stable with a wide range of
output capacitors. A minimum output capacitor of 1.5µF
is required to prevent oscillations. The LT1521 is a
micropower device and output transient response will be
a function of output capacitance. See the Transient
Response curves in the Typical Performance Characteris-
tics. Larger values of output capacitance will decrease the
peak deviations and provide improved output transient
response for larger load current deltas. Bypass capaci-
tors, used to decouple individual components powered by
the LT1521, will increase the effective value of the output
capacitor.
Protection Features
The LT1521 incorporates several protection features which
make it ideal for use in battery-powered circuits. In
addition to the normal protection features associated with
monolithic regulators, such as current limiting and ther-
mal limiting, the device is protected against reverse input
voltages, reverse output voltages and reverse voltages
from output to input.
Current limit protection and thermal overload protection
are intended to protect the device against current overload
conditions at the output of the device. For normal opera-
tion, the junction temperatures should not exceed 125°C.
The input of the device will withstand reverse voltages of
20V. Current flow into the device will be limited to less
than 1mA (typically less than 100µA) and no negative
voltage will appear at the output. The device will protect
both itself and the load. This provides protection against
batteries that can be plugged in backward.
For fixed voltage versions of the device, the output can be
pulled below ground without damaging the device. If the
input is left open circuit or grounded, the output can be
pulled below ground by 20V. The output will act like an
open circuit, no current will flow out of the pin. If the input
is powered by voltage source, the output will source the
short-circuit current of the device and will protect itself by
thermal limiting. For the adjustable version of the device,
the output pin is internally clamped at one diode drop
below ground. Reverse current for the adjustable device
must be limited to 5mA.
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LT1521CS8-3.3.PDF ] | |
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