Datasheet

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LT1528

1528fa

■

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

= 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 capaci-

tor ESR. Dropout voltage is 75mV at 10mA, rising to

300mV at 1A and 600mV at 3A. The device has a quiescent

current of 400µA. Quiescent current is well controlled; it

does not increase significantly as the device enters drop-

out. 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 microproces-

sor applications. The LT1528 is available with a fixed

output voltage of 3.3V. An external SENSE pin allows

adjustment to output voltages greater than 3.3V, using a

simple resistive 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

available in 5-lead TO-220 and 5-lead DD packages.

3A Low Dropout Regulator

for Microprocessor Applications

Microprocessor Supply with Shutdown

OUTPUT CURRENT (mA)

DROPOUT VOLTAGE (V)

0.1

0.2

0.3

0.4

0.6

0.5

1.0 1.5 2.0

LT1528 • TA02

2.5 3.0

0.5

Dropout Voltage

, LTC and LT are registered trademarks of Linear Technology Corporation.

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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

=5V

4 × 47µF*

SOLID TANTALUM

OUT

SHDN

(PIN 4) OUTPUT

<0.25 OFF

>2.80 ON

NC ON

SHORTING V

OUT

J1 3.30

J2 3.45

J3 4.00

LT1528 • TA01

GND

SHDN

OUT

SENSE

J1 J2 J3

15Ω 68Ω

330Ω

LT1528

*CHOOSE CAPACITORS

TO MEET PROCESSOR

REQUIREMENTS

DESCRIPTIO

FEATURES

APPLICATIO S

TYPICAL APPLICATIO

Summary of content (12 pages)

PAGE 1
LT1528 3A Low Dropout Regulator for Microprocessor Applications U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO 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.
PAGE 2
LT1528 W W W AXI U U ABSOLUTE RATI GS (Note 1) Input Voltage ....................................................... ±15V* OUTPUT Pin Reverse Current ............................... 10mA SENSE Pin Current ............................................... 10mA SHDN Pin Input Voltage (Note 2) ................ 6.5V, – 0.3V SHDN Pin Input Current (Note 2) ........................... 5mA Output Short-Circuit Duration .......................... Indefinite Storage Temperature Range .................
PAGE 3
LT1528 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25°C. PARAMETER CONDITIONS TYP MAX UNITS GND Pin Current (Note 6) ILOAD = 0mA ILOAD = 0mA, TJ = 125°C (Note 7) MIN 450 1.9 750 µA mA ILOAD = 100mA ILOAD = 100mA, TJ = 125°C (Note 7) ILOAD = 300mA ILOAD = 300mA, TJ = 125°C (Note 7) 1.2 2.7 2.5 mA mA 2.6 4.1 4.0 mA mA ILOAD = 700mA ILOAD = 700mA, TJ = 125°C (Note 7) ILOAD = 1.5A 7.
PAGE 4
LT1528 U W TYPICAL PERFOR A CE CHARACTERISTICS Guaranteed Dropout Voltage = TEST POINTS 0.9 0.7 DROPOUT VOLTAGE (V) DROPOUT VOLTAGE (V) 0.8 TJ ≤ 125°C 0.6 0.5 TJ ≤ 25°C 0.4 0.3 0.2 Quiescent Current 0.8 2.00 0.7 1.75 ILOAD = 3A 0.6 0.5 ILOAD = 1.5A 0.4 ILOAD = 700mA 0.3 0.2 ILOAD = 300mA 0.1 0.1 0 0 0.5 1.5 2.0 1.0 OUTPUT CURRENT (A) ILOAD = 10mA 0 –50 3.0 2.5 QUIESCENT CURRENT (mA) 1.0 Dropout Voltage –25 75 50 25 TEMPERATURE (°C) 0 100 VIN = 4.3V RL = ∞ 1.50 1.25 1.
PAGE 5
LT1528 U W TYPICAL PERFOR A CE CHARACTERISTICS 1.8 90 ILOAD = 3A 1.4 1.2 ILOAD = 1mA 1.0 0.8 0.6 80 70 60 50 40 30 0.4 20 0.
PAGE 6
LT1528 U W TYPICAL PERFOR A CE CHARACTERISTICS Ripple Rejection Load Regulation 80 0 VIN = VOUT(NOMINAL) + 1V ∆ILOAD = 1mA TO 3A 70 60 50 LOAD REGULATION (mV) RIPPLE REJECTION (dB) –5 COUT = 4 × 47µF SOLID TANTALUM 40 COUT = 47µF SOLID TANTALUM 30 20 0 10 100 1k 10k FREQUENCY (Hz) –15 –20 –25 IOUT = 1.
PAGE 7
LT1528 U U U PI FU CTIO S SHDN (Pin 4): This pin is used to put the device into shutdown. In shutdown the output of the device is turned off. This pin is active low. The device will be shut down if the SHDN pin is actively pulled low. The SHDN pin current with the pin pulled to ground will be 60µA. The SHDN pin is internally clamped to 7V and – 0.6V (one VBE). This allows the SHDN pin to be driven directly by 5V logic or by open collector logic with a pull-up resistor.
PAGE 8
LT1528 U W U U APPLICATIO S I FOR ATIO The LT1528 is specified with the SENSE pin tied to the OUTPUT pin. This sets the output voltage to 3.3V. Specifications for output voltage greater than 3.3V will be proportional to the ratio of the desired output voltage to 3.3V (VOUT/3.3V). For example, load regulation for an output current change of 1mA to 1.5A is – 5mV (typical) at VOUT = 3.3V. At VOUT = 12V, load regulation would be: (12V/3.
PAGE 9
LT1528 U W U U APPLICATIO S I FOR ATIO The maximum junction temperature will be equal to the maximum junction temperature rise above ambient plus the maximum ambient temperature or: different processors. This application allows the output voltage to be jumper selectable. Protection Features TJMAX = 50°C + 31.4°C = 81.4°C Output Capacitance and Transient Performance The LT1528 is designed to be stable with a wide range of output capacitors. The minimum recommended value is 3.
PAGE 10
LT1528 U W U U APPLICATIO S I FOR ATIO The reverse output current will follow the curve in Figure 3 when the input is pulled to ground. This current flows through the OUTPUT pin to ground. The state of the SHDN pin will have no effect on output current when the input pin is pulled to ground. In some applications it may be necessary to leave the input on the LT1528 unconnected when the output is held high. This can happen when the LT1528 is powered from a rectified AC source.
PAGE 11
LT1528 U PACKAGE DESCRIPTIO Q Package 5-Lead Plastic DD Pak (Reference LTC DWG # 05-08-1461) 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 ( +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.
PAGE 12
LT1528 U PACKAGE DESCRIPTIO T Package 5-Lead Plastic TO-220 (Standard) (Reference LTC DWG # 05-08-1421) 0.165 – 0.180 (4.191 – 4.572) 0.147 – 0.155 (3.734 – 3.937) DIA 0.390 – 0.415 (9.906 – 10.541) 0.045 – 0.055 (1.143 – 1.397) 0.230 – 0.270 (5.842 – 6.858) 0.570 – 0.620 (14.478 – 15.748) 0.460 – 0.500 (11.684 – 12.700) 0.620 (15.75) TYP 0.330 – 0.370 (8.382 – 9.398) 0.700 – 0.728 (17.78 – 18.491) 0.095 – 0.115 (2.413 – 2.921) SEATING PLANE 0.152 – 0.202 0.260 – 0.320 (3.861 – 5.131) (6.