PRODUCT DATASHEET
AAT3221/2
PowerLinearTM
150mA NanoPower™ LDO Linear Regulator
X7R, X5R, Z5U, and Y5V dielectric materials. Large
ceramic capacitors, typically greater than 2.2μF, are often
available in low-cost Y5V and Z5U dielectrics. These two
material types are not recommended for use with LDO
regulators since the capacitor tolerance can vary more
than ±50% over the operating temperature range of the
device. A 2.2μF Y5V capacitor could be reduced to 1μF
over the full operating temperature range. This can cause
problems for circuit operation and stability. X7R and X5R
dielectrics are much more desirable. The temperature
tolerance of X7R dielectric is better than ±15%.
rapidly increase. Once the regulator’s power dissipation
capacity has been exceeded and the internal die tem-
perature reaches approximately 140°C, the system ther-
mal protection circuit will become active. The internal
thermal protection circuit will actively turn off the LDO
regulator output pass device to prevent the possibility of
over-temperature damage. The LDO regulator output will
remain in a shutdown state until the internal die tem-
perature falls back below the 140°C trip point.
The interaction between the short-circuit and thermal
protection systems allows the LDO regulator to with-
stand indefinite short-circuit conditions without sustain-
ing permanent damage.
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 equiva-
lent material and capacitance value. These larger devic-
es can also improve circuit transient response when
compared to an equal value capacitor in a smaller pack-
age size.
No-Load Stability
The AAT3221/2 is designed to maintain output voltage
regulation and stability under operational no-load condi-
tions. This is an important characteristic for applications
where the output current may drop to zero. An output
capacitor is required for stability under no-load operating
conditions. Refer to the output capacitor considerations
section of this document for recommended typical out-
put capacitor values.
Consult capacitor vendor datasheets carefully when
selecting capacitors for use with LDO regulators.
Enable Function
The AAT3221/2 features an LDO regulator enable / dis-
able function. This pin (EN) is compatible with CMOS
logic. Active high or active low options are available (see
Ordering Information). For a logic high signal, the EN
control level must be greater than 2.4 volts. A logic low
signal is asserted when the voltage on the EN pin falls
below 0.6 volts. For example, the active high version
AAT3221/2 will turn on when a logic high is applied to
the EN pin. If the enable function is not needed in a spe-
cific application, it may be tied to the respective voltage
level to keep the LDO regulator in a continuously on
state; e.g., the active high version AAT3221/2 will tie VIN
to EN to remain on.
Thermal Considerations and High Output
Current Applications
The AAT3221/2 is designed to deliver a continuous out-
put load current of 150mA under normal operating con-
ditions. The limiting characteristic for the maximum
output load safe operating area is essentially package
power dissipation and the internal preset thermal limit of
the device. In order to obtain high operating currents,
careful device layout and circuit operating conditions
need to be taken into account. The following discussions
will assume the LDO regulator is mounted on a printed
circuit board utilizing the minimum recommended foot-
print and the printed circuit board is 0.062-inch thick
FR4 material with one ounce copper.
Short-Circuit Protection and Thermal
Protection
The AAT3221/2 is protected by both current limit and
over-temperature protection circuitry. The internal short-
circuit current limit is designed to activate when the
output load demand exceeds the maximum rated output.
If a short-circuit condition were to continually draw more
than the current limit threshold, the LDO regulator’s out-
put voltage will drop to a level necessary to supply the
current demanded by the load. Under short-circuit or
other over-current operating conditions, the output volt-
age will drop and the AAT3221/2 die temperature will
At any given ambient temperature (TA), the maximum
package power dissipation can be determined by the fol-
lowing equation:
TJ(MAX) - TA
θJA
PD(MAX)
=
Constants for the AAT3221/2 are TJ(MAX), the maximum
junction temperature for the device which is 125°C and
ΘJA = 150°C/W, the package thermal resistance. Typically,
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3221.2007.11.1.12
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