AAT3223
250mA NanoPower™ LDO
Linear Regulator with Power-OK
needed can be calculated from the step size of the
change in output load current expected and the
voltage excursion that the load can tolerate.
Applications Information
To assure the maximum possible performance is
obtained from the AAT3223, please refer to the fol-
lowing application recommendations.
The total output capacitance required can be cal-
culated using the following formula:
Input Capacitor
∆I
COUT
=
× 15µF
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 AAT3223 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 pos-
sible. CIN values greater than 1µF will offer superi-
or input line transient response and will assist in
maximizing the power supply ripple rejection.
∆V
Where:
∆I = maximum step in output current
∆V = 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 AAT3223 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.
Ceramic, tantalum, or aluminum electrolytic capac-
itors may be selected for CIN, as there is no specif-
ic capacitor ESR requirement. For 250mA LDO
regulator output operation, ceramic capacitors are
recommended for CIN due to their inherent capabil-
ity over tantalum capacitors to withstand input cur-
rent surges from low impedance sources, such as
batteries in portable devices.
Capacitor Characteristics
Output Capacitor
Ceramic composition capacitors are highly recom-
mended over all other types of capacitors for use
with the AAT3223. 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 incorrectly connected.
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 AAT3223 has been specifically
designed to function with very low ESR ceramic
capacitors. Although the device is intended to oper-
ate 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 elec-
trolytic capacitors. However, for best performance,
ceramic capacitors are recommended.
Equivalent Series Resistance: ESR is a very
important characteristic to consider when selecting
a capacitor. ESR is the internal series resistance
associated with a capacitor that includes lead
resistance, internal connections, capacitor size and
area, material composition, and ambient tempera-
ture. Typically, capacitor ESR is measured in mil-
liohms for ceramic capacitors and can range to
more than several ohms for tantalum or aluminum
electrolytic capacitors.
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
application, then an increased value for COUT
should be considered. The amount of capacitance
10
3223.2006.03.1.5
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
