LP3891

0.8A Fast-Response Ultra Low Dropout Linear

Regulators

General Description

The LP3891 is a high current, fast response regulator which

can maintain output voltage regulation with minimum input to

output voltage drop. Fabricated on a CMOS process, the

device operates from two input voltages: Vbias provides

voltage to drive the gate of the N-MOS power transistor,

while Vin is the input voltage which supplies power to the

load. The use of an external bias rail allows the part to

operate from ultra low Vin voltages. Unlike bipolar regula-

tors, the CMOS architectutre consumes extremely low qui-

escent current at any output load current. The use of an

N-MOS power transistor results in wide bandwidth, yet mini-

mum external capacitance is required to maintain loop sta-

bility.

The fast transient response of these devices makes them

suitable for use in powering DSP, Microcontroller Core volt-

ages and Switch Mode Power Supply post regulators. The

parts are available in TO-220 and TO-263 packages.

Ground Pin Current: 3 mA (typ) at full load.

Shutdown Current: 60 nA (typ) when S/D pin is low.

Precision Output Voltage: 1.5% room temperature accu-

racy.

Features

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Low ground pin current

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Load regulation of 0.04%/A

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60 nA typical quiescent current in shutdown

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1.5% output accuracy (25˚C)

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TO-220, TO-263 packages

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Over temperature/over current protection

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−40˚C to +125˚C junction temperature range

Applications

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DSP Power Supplies

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Server Core and I/O Supplies

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PC Add-in-Cards

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Local Regulators in Set-Top Boxes

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Microcontroller Power Supplies

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High Efficiency Power Supplies

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SMPS Post-Regulators

Typical Application Circuit

20069501

At least 10 µF of input and output capacitance is required for stability.

*Tantalum capacitors are recommended. Aluminum electrolytic capacitors may be used for restricted temperature range. See application hints.

Connection Diagrams

20069502

TO-220, Top View

20069503

TO-263, Top View

September 2003

© 2003 National Semiconductor Corporation

DS200695

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