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AAT3221

150mA NanoPower™ LDO Linear Regulator

Advanced Analogic Technologies 

PowerLinearTM

PRODUCT DATASHEET

AAT3221/2

150mA NanoPower™ LDO Linear Regulator

Applications Information

To ensure that the maximum possible performance is

obtained from the AAT3221/2, please refer to the follow-

ing application recommendations.

Input Capacitor

A 1μF or larger capacitor is typically recommended for

CIN in most applications. A CIN capacitor is not required

for basic LDO regulator operation. However, if the

AAT3221/2 is physically located any distance more than

one or two centimeters from the 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 power supply ripple rejection.

Ceramic, tantalum, or aluminum electrolytic capacitors

may be selected for CIN, as there is no specific capacitor

ESR requirement. 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 sta-

bility, 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 pos-

sible for maximum device performance. The AAT3221/2

has been specifically designed to function with very low

ESR ceramic capacitors. Although the device is intended

to operate with these low ESR capacitors, it is stable

over a wide range of capacitor ESR, thus it will also work

with some higher ESR tantalum or aluminum electrolytic

capacitors. However, for best performance, ceramic

capacitors are recommended.

The value of COUT typically ranges from 0.47μF to 10μF;

however, 1μF is sufficient for most operating conditions.

If large output current steps are required by an applica-

tion, then an increased value for COUT should be consid-

ered. The amount of capacitance needed can be calcu-

lated from the step size of the change in output load

current expected and the voltage excursion that the load

can tolerate.

The total output capacitance required can be calculated

using the following formula:

ΔI

COUT = ΔV · 15µF

Where:

ΔI = maximum step in output current

ΔV = 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 AAT3221/2 at room temperature. The increased

capacitor value is recommended if tight output toler-

ances must be maintained over extreme operating con-

ditions and maximum operational temperature excur-

sions. If tantalum or aluminum electrolytic capacitors

are used, the capacitor value should be increased to

compensate for the substantial ESR inherent to these

capacitor types.

Capacitor Characteristics

Ceramic composition capacitors are highly recommend-

ed over all other types of capacitors for use with the

AAT3221/2. Ceramic capacitors offer many advantages

over their tantalum and aluminum electrolytic counter-

parts. A ceramic capacitor typically has very low ESR, is

lower cost, has a smaller PCB footprint, and is non-

polarized. Line and load transient response of the LDO

regulator is improved by using low-ESR ceramic capaci-

tors. Since ceramic capacitors are non-polarized, they

are less prone to damage if incorrectly connected.

Equivalent Series Resistance (ESR)

ESR is a very important characteristic to consider when

selecting a capacitor. ESR is the internal series resis-

tance 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 0.1μF are typically made

from NPO or C0G materials. NPO and C0G materials are

typically tight tolerance and very stable over tempera-

ture. Larger capacitor values are typically composed of

3221.2007.11.1.12

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