AAT3237 Datasheet, PDF(9/13 Page) Advanced Analogic Technologies

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AAT3237 Datasheet, PDF (9/13 Pages) Advanced Analogic Technologies – 300mA MicroPower™ LDO with PowerOK

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AAT3237

300mA MicroPowerâ¢ LDO with PowerOK

Applications Information

To assure the maximum possible performance is

obtained from the AAT3237, please refer to the fol-

lowing application recommendations.

Input Capacitor

Typically, a 1ÂµF 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 AAT3237 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

1ÂµF 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 AAT3237 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 output

current conditions range from 1ÂµF to 10ÂµF.

Applications utilizing the exceptionally low output

noise and optimum power supply ripple rejection

characteristics of the AAT3237 should use 2.2ÂµF 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 0.47ÂµF.

3237.2006.01.1.4

Capacitor Characteristics

Ceramic composition capacitors are highly recom-

mended over all other types of capacitors for use

with the AAT3237. Ceramic capacitors offer many

advantages over their tantalum and aluminum elec-

trolytic counterparts. A ceramic capacitor typically

has very low ESR, is lower cost, has a smaller PCB

footprint, and is non-polarized. Line and load tran-

sient response of the LDO regulator is improved by

using low ESR ceramic capacitors. Since ceramic

capacitors are non-polarized, they are not prone to

incorrect connection damage.

Equivalent Series Resistance: ESR is a very

important characteristic to consider when selecting a

capacitor. ESR is the internal series resistance asso-

ciated with a capacitor that includes lead resistance,

internal connections, size and area, material compo-

sition, and ambient temperature. Typically, capacitor

ESR is measured in milliohms for ceramic capacitors

and can range to more than several ohms for tanta-

lum or aluminum electrolytic capacitors.

Ceramic Capacitor Materials: Ceramic capaci-

tors less than 0.1ÂµF are typically made from NPO

or C0G materials. NPO and C0G materials gener-

ally have tight tolerance and are very stable over

temperature. Larger capacitor values are usually

composed of X7R, X5R, Z5U, or Y5V dielectric

materials. These two material types are not recom-

mended for use with LDO regulators since the

capacitor tolerance can vary more than Â±50% over

the operating temperature range of the device. A

2.2ÂµF Y5V capacitor could be reduced to 1ÂµF over

temperature; this could cause problems for circuit

operation. X7R and X5R dielectrics are much more

desirable. The temperature tolerance of X7R

dielectric is better than Â±15%.

Capacitor area is another contributor to ESR.

Capacitors that are physically large in size will have

a lower ESR when compared to a smaller sized

capacitor of an equivalent material and capacitance

value. These larger devices can improve circuit tran-

sient response when compared to an equal value

capacitor in a smaller package size.

Consult capacitor vendor datasheets carefully

when selecting capacitors for LDO regulators.

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