AAT3220
150mA NanoPower™ LDO Linear Regulator
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.
Ceramic Capacitor Materials:
Ceramic capacitors
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 rec-
ommended for use with LDO regulators since the
capacitor tolerance can vary by 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%.
Capacitor area is another contributor to ESR.
Capacitors, which are physically large in size will
have a lower ESR when compared to a smaller
sized capacitor of equivalent material and capaci-
tance value. These larger devices can also improve
circuit transient response when compared to an
equal value capacitor in a smaller package size.
Consult capacitor vendor datasheets carefully when
selecting capacitors for use with LDO regulators.
rent demanded by the load. Under short-circuit or
other over-current operating conditions, the output
voltage would drop and the AAT3220's die temper-
ature would increase rapidly. Once the regulator's
power dissipation capacity has been exceeded and
the internal die temperature reaches approximate-
ly 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.
The combination and interaction between the short-
circuit and thermal protection systems allows the
LDO regulator to withstand indefinite short-circuit
conditions without sustaining permanent damage.
No-Load Stability
The AAT3220 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.
Thermal Considerations and High
Output Current Applications
The AAT3220 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 AAT3220 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
to continually draw more than the current limit
threshold, the LDO regulator's output voltage
would drop to a level necessary to supply the cur-
10
3220.2006.01.1.4
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
