AAT3220 Datasheet, PDF(9/16 Page) Advanced Analogic Technologies

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AAT3220 Datasheet, PDF (9/16 Pages) Advanced Analogic Technologies – 150mA NanoPower™ LDO Linear Regulator

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AAT3220

150mA NanoPowerâ¢ LDO Linear Regulator

Applications Information

To assure the maximum possible performance is

obtained from the AAT3220, please refer to the fol-

lowing application recommendations.

Input Capacitor

Typically a 1ÂµF or larger capacitor is recommended

for CIN in most applications. A CIN capacitor is not

required for basic LDO regulator operation.

However, if the AAT3220 is physically located any

distance more than a centimeter or two from the

input power source, a CIN capacitor will be needed

for stable operation. CIN should be located as close

to the device VIN pin as practically possible. CIN val-

ues 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 capaci-

tors may be selected for CIN. There is no specific

capacitor ESR requirement for CIN. For 150mA

LDO regulator output operation, ceramic capacitors

are recommended for CIN due to their inherent

capability over tantalum capacitors to withstand

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 per-

formance. The AAT3220 has been specifically

designed to function with very low ESR ceramic

capacitors. Although the device is intended to oper-

ate with low ESR capacitors, it is stable over a very

wide range of capacitor ESR, thus it will also work

with some higher ESR tantalum or aluminum elec-

trolytic capacitors. However, for best performance,

ceramic capacitors are recommended.

The value of COUT typically ranges from 0.47ÂµF to

10ÂµF, however 1ÂµF is sufficient for most operating

conditions.

If large output current steps are required by an

application, then an increased value for COUT

should be considered. The amount of capacitance

needed can be calculated from the step size of the

change in the output load current expected and the

voltage excursion that the load can tolerate.

3220.2001.09.1.0

The total output capacitance required can be cal-

culated using the following formula:

COUT

âI

âV

15ÂµF

Where:

âI = maximum step in output current

âV = maximum excursion in voltage that the load

can tolerate

Note that use of this equation results in capacitor

values approximately two to four times the typical

value needed for an AAT3220 at room temperature.

The increased capacitor value is recommended if

tight output tolerances must be maintained over

extreme operating conditions and maximum opera-

tional temperature excursions. If tantalum or alu-

minum electrolytic capacitors are used, the capaci-

tor value should be increased to compensate for the

substantial ESR inherent to these capacitor types.

Capacitor Characteristics

Ceramic composition capacitors are highly recom-

mended over all other types of capacitors for use

with the AAT3220. 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 less prone

to damage if connected incorrectly.

Equivalent Series Resistance (ESR): ESR is a

very important characteristic to consider when

selecting a capacitor. ESR is the internal series

resistance associated with a capacitor, which

includes lead resistance, internal connections,

capacitor size and area, material composition and

ambient temperature. Typically capacitor ESR is

measured in milliohms for ceramic capacitors and

can range to more than several ohms for tantalum

or aluminum electrolytic capacitors.

Ceramic Capacitor Materials: Ceramic capacitors

less than 0.1ÂµF are typically made from NPO or

COG materials. NPO and COG materials are typi-

cally tight tolerance and very stable over tempera-

ture. Larger capacitor values are typically composed

of X7R, X5R, Z5U or Y5V dielectric materials. Large

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