AAT3223_06 Datasheet, PDF (10/17 Pages) Advanced Analogic Technologies – 250mA NanoPower™ LDO Linear Regulator with Power-OK

Applications Information
To assure the maximum possible performance is
obtained from the AAT3223, please refer to the fol-
lowing application recommendations.
Input Capacitor
Typically, a 1µF or larger capacitor is recommend-
ed for C_IN in most applications. A C_IN 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 C_IN capacitor will be
needed for stable operation. C_IN should be located
as closely to the device V_IN pin as practically pos-
sible. C_IN values greater than 1µF will offer superi-
or input line transient response and will assist in
maximizing the power supply ripple rejection.
Ceramic, tantalum, or aluminum electrolytic capac-
itors may be selected for C_IN, as there is no specif-
ic capacitor ESR requirement. For 250mA LDO
regulator output operation, ceramic capacitors are
recommended for C_IN 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.
Output Capacitor
For proper load voltage regulation and operational
stability, a capacitor is required between pins V_OUT
and GND. The C_OUT 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.
The value of C_OUT 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 C_OUT
should be considered. The amount of capacitance
10
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.
The total output capacitance required can be cal-
culated using the following formula:
C_OUT =
∆I
∆V
× 15µF
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.
Capacitor Characteristics
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.
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.
3223.2006.03.1.5