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LT1528
1
1528fb
TYPICAL APPLICATION
DESCRIPTION
3A Low Dropout Regulator
for Microprocessor Applications
FEATURES
APPLICATIONS
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Dropout Voltage: 0.6V at I
OUT
= 3A
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Fast Transient Response
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Output Current: 3A
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Quiescent Current: 400μA
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No Protection Diodes Needed
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Fixed Output Voltage: 3.3V
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Controlled Quiescent Current in Dropout
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Shutdown I
Q
= 125μA
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Stable with 3.3μF Output Capacitor
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Reverse Battery Protection
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No Reverse Output Current
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Thermal Limiting
The LT
®
1528 is a 3A low dropout regulator optimized to
handle the large load current transients associated with
the current generation of microprocessors. This device has
the fastest transient response of currently available PNP
regulators and is very tolerant of variations in capacitor
ESR. Dropout voltage is 75mV at 10mA, rising to 300mV
at 1A and 600mV at 3A. The device has a quiescent cur-
rent of 400μA. Quiescent current is well controlled; it does
not increase signifi cantly as the device enters dropout.
The regulator can operate with output capacitors as small
as 3.3μF, although larger capacitors will be needed to
achieve the performance required in most microprocessor
applications. The LT1528 is available with a fi xed output
voltage of 3.3V. An external SENSE pin allows adjustment
to output voltages greater than 3.3V, using a simple resis-
tive divider. This allows the device to be adjusted over a
wide range of output voltages, including the 3.3V to 4.2V
range required by a variety of processors from Intel, IBM,
AMD, and Cyrix.
The LT1528 has both reverse input and reverse output
protection and includes a shutdown feature. Quiescent
current drops to 125μA in shutdown. The LT1528 is avail-
able in 5-lead TO-220 and 5-lead DD-PAK packages.
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Microprocessor Applications
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Post Regulator for Switching Supplies
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5V to 3.3V Logic Regulator
Microprocessor Supply with Shutdown
OUTPUT CURRENT (mA)
0
0
DROPOUT VOLTAGE (V)
0.1
0.2
0.3
0.4
0.6
0.5
1.0 1.5 2.0
1528 TA02
2.5 3.0
0.5
Dropout Voltage
5
4
1
2
3
+
V
IN
=5V
4 × 47μF*
SOLID TANTALUM
V
OUT
V
SHDN
(PIN 4) OUTPUT
<0.25 OFF
>2.80 ON
NC ON
SHORTING V
OUT
J1 3.30
J2 3.45
J3 4.00
1528 TA01
GND
IN
SHDN
OUT
SENSE
J1 J2 J3
15Ω 68Ω
330Ω
LT1528
*CHOOSE CAPACITORS
TO MEET PROCESSOR
REQUIREMENTS
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
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