AAT3238IJS-2.5-T1(2006) 데이터 시트보기 (PDF) - Advanced Analogic Technologies

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AAT3238IJS-2.5-T1
(Rev.:2006)

300mA MicroPower™ High Performance LDO Linear Regulator

Advanced Analogic Technologies 

AAT3238

300mA MicroPower™

High Performance LDO Linear Regulator

Applications Information

To assure the maximum possible performance is

obtained from the AAT3238, please refer to the fol-

lowing application recommendations.

Input Capacitor

Typically, a 1µF or larger capacitor is recommend-

ed for CIN in most applications. A CIN capacitor is

not required for basic LDO regulator operation.

However, if the AAT3238 is physically located more

than three centimeters from an input power source,

a CIN capacitor will be needed for stable operation.

CIN should be located as closely to the device VIN

pin as practically possible. CIN values greater than

1µF will offer superior input line transient response

and will assist in maximizing the highest possible

power supply ripple rejection.

Ceramic, tantalum, or aluminum electrolytic capac-

itors may be selected for CIN. There is no specific

capacitor ESR requirement for CIN. However, for

300mA LDO regulator output operation, ceramic

capacitors are recommended for CIN due to their

inherent capability over tantalum capacitors to with-

stand input current surges from low impedance

sources such as batteries in portable devices.

Output Capacitor

For proper load voltage regulation and operational

stability, a capacitor is required between pins VOUT

and GND. The COUT capacitor connection to

the LDO regulator ground pin should be made as

direct as practically possible for maximum device

performance.

The AAT3238 has been specifically designed to func-

tion with very low ESR ceramic capacitors. For best

performance, ceramic capacitors are recommended.

Typical output capacitor values for maximum out-

put current conditions range from 1µF to 10µF.

Applications utilizing the exceptionally low output

noise and optimum power supply ripple rejection

characteristics of the AAT3238 should use 2.2µF or

greater for COUT. If desired, COUT may be

increased without limit.

In low output current applications where output

load is less than 10mA, the minimum value for

COUT can be as low as 0.47µF.

Bypass Capacitor and Low Noise

Applications

A bypass capacitor pin is provided to enhance the

low noise characteristics of the AAT3238 LDO reg-

ulator. The bypass capacitor is not necessary for

operation of the AAT3238. However, for best

device performance, a small ceramic capacitor

should be placed between the bypass pin (BYP)

and the device ground pin (GND). The value of

CBYP may range from 470pF to 10nF. For lowest

noise and best possible power supply ripple rejec-

tion performance, a 10nF capacitor should be

used. To practically realize the highest power sup-

ply ripple rejection and lowest output noise per-

formance, it is critical that the capacitor connection

between the BYP pin and GND pin be direct and

PCB traces should be as short as possible. Refer

to the PCB Layout Recommendations section of

this document for examples.

There is a relationship between the bypass capac-

itor value and the LDO regulator turn-on and turn-

off time. In applications where fast device turn-on

and turn-off time are desired, the value of CBYP

should be reduced.

In applications where low noise performance and/

or ripple rejection are less of a concern, the bypass

capacitor may be omitted. The fastest device turn-

on time will be realized when no bypass capacitor

is used.

DC leakage on this pin can affect the LDO regula-

tor output noise and voltage regulation perform-

ance. For this reason, the use of a low leakage,

high quality ceramic (NPO or C0G type) or film

capacitor is highly recommended.

Capacitor Characteristics

Ceramic composition capacitors are highly recom-

mended over all other types of capacitors for use

with the AAT3238. Ceramic capacitors offer many

advantages over their tantalum and aluminum elec-

trolytic counterparts. A ceramic capacitor typically

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