AAT3201
150mA OmniPower™ LDO Linear Regulator
Ceramic Capacitor Materials: Ceramic capacitors
to continually draw more than the current limit
threshold, the LDO regulator's output voltage would
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 would drop and the AAT3201's die temperature
would rapidly increase. Once the regulator's power
dissipation capacity has been exceeded and the
internal die temperature reaches approximately
140°C the system thermal protection circuit will
become active. The internal thermal protection cir-
cuit will actively turn off the LDO regulator output
pass device to prevent the possibility of over-tem-
perature damage. The LDO regulator output will
remain in a shutdown state until the internal die
temperature falls back below the 140°C trip point.
less than 0.1µF are typically made from NPO or
C0G materials. NPO and C0G materials generally
have tight tolerance and are very stable over tem-
perature. Larger capacitor values are usually com-
posed of X7R, X5R, Z5U, or Y5V dielectric materi-
als. Large ceramic capacitors (i.e., greater than
2.2µF) are often available in low-cost Y5V and Z5U
dielectrics. These two material types are not recom-
mended for use with LDO regulators since the capac-
itor 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 prob-
lems for circuit operation and stability. X7R and X5R
dielectrics are much more desirable. The tempera-
ture tolerance of X7R dielectric is better than ±15%.
The interaction between the short-circuit and ther-
mal protection systems allows the LDO regulator to
withstand indefinite short-circuit conditions without
sustaining 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 equivalent material and capacitance
value. These larger devices can also improve cir-
cuit transient response when compared to an equal
value capacitor in a smaller package size.
No-Load Stability
The AAT3201 is designed to maintain output volt-
age regulation and stability under operational no-
load conditions. 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 section of this datasheet for rec-
ommended typical output capacitor values.
Consult capacitor vendor datasheets carefully when
selecting capacitors for use with LDO regulators.
Enable Function
The AAT3201 features an LDO regulator enable /
disable function. This pin (EN) is active high and is
compatible with CMOS logic. To assure the LDO
regulator will switch on, the EN turn-on control level
must be greater than 2.4V. The LDO regulator will
go into the disable shutdown mode when the volt-
age on the EN pin falls below 0.6V. If the enable
function is not needed in a specific application, it
may be tied to VIN to keep the LDO regulator in a
continuously on state.
Thermal Considerations and High
Output Current Applications
The AAT3201 is designed to deliver a continuous
output load current of 150mA under normal operat-
ing conditions. The limiting characteristic for the
maximum output load safe operating area is essen-
tially package power dissipation and the internal pre-
set 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 reg-
ulator is mounted on a printed circuit board utilizing
the minimum recommended footprint and the print-
ed circuit board is 0.062-inch thick FR4 material with
one ounce copper.
Short-Circuit and Thermal Protection
The AAT3201 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 maxi-
mum rated output. If a short-circuit condition were
10
3201.2006.01.1.2
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