AAT3258ITS-2.8-R-T1 datasheet(10/16 Pages) ANALOGICTECH

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AAT3258

300mA LDO Linear Regulator with µP Reset

3258.2006.03.1.6

Functional Description

The AAT3258 is intended for LDO regulator applica-

tions where output current load requirements range

from no load to 300mA.

The advanced circuit design of the AAT3258 has

been specifically optimized for very fast start-up and

shutdown timing. This proprietary CMOS LDO has

also been tailored for superior transient response

characteristics. These traits are particularly impor-

tant for applications that require fast power supply

timing, such as GSM cellular telephone handsets.

The high-speed turn-on capability is enabled

through the implementation of a fast start control cir-

cuit, which accelerates the power-up behavior of

fundamental control and feedback circuits within the

LDO regulator.

Fast turn-off response time is achieved by an active

output pull-down circuit, which is enabled when the

LDO regulator is placed in the shutdown mode. This

active fast shutdown circuit has no adverse effect on

normal device operation.

The AAT3258 has very fast transient response char-

acteristics, which is an important feature for applica-

tions where fast line and load transient response is

required. This rapid transient response behavior is

accomplished through the implementation of an

active error amplifier feedback control. This propri-

etary circuit design is unique to this MicroPower

LDO regulator.

The LDO regulator output has been specifically opti-

mized to function with low-cost, low-ESR ceramic

capacitors; however, the design will allow for opera-

tion over a wide range of capacitor types.

A bypass pin has been provided to allow the addition

of an optional voltage reference bypass capacitor to

reduce output self noise and increase power supply

ripple rejection. Device self noise and PSRR will be

improved by the addition of a small ceramic capaci-

tor in this pin. However, increased values of C

BYPASS

may slow down the LDO regulator turn-on time.

This LDO regulator has complete short-circuit and

thermal protection.

The integral combination of

these two internal protection circuits gives the

AAT3258 a comprehensive safety system to guard

against extreme adverse operating conditions.

Device power dissipation is limited to the package

type and thermal dissipation properties. Refer to the

Thermal Considerations section of this datasheet for

details on device operation at maximum output cur-

rent loads.

Functional Block Diagram

Oscillator

Voltage

Reference

VDET

RESET

GND

Error

Amplifier

Over-Current

Protection

Over-

Temperature

Protection

Voltage

Reference

VIN

SHDN

BYP

OUT

Reset Generator

and Timer

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