AAT3215
150mA CMOS High Performance LDO
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 not prone to
incorrect connection damage.
age on the EN pin falls below 0.6 volts. If the
enable function is not needed in a specific applica-
tion, it may be tied to VIN to keep the LDO regula-
tor in a continuously on state.
When the LDO regulator is in shutdown mode, an
internal 1.5kΩ resistor is connected between VOUT
and GND. This is intended to discharge COUT when
the LDO regulator is disabled. The internal 1.5kΩ
has no adverse effect on device turn-on time.
Equivalent Series Resistance: ESR is a very
important characteristic to consider when selecting a
capacitor. ESR is the internal series resistance asso-
ciated with a capacitor that includes lead resistance,
internal connections, size and area, material compo-
sition, and ambient temperature. Typically, capacitor
ESR is measured in milliohms for ceramic capacitors
and can range to more than several ohms for tanta-
lum or aluminum electrolytic capacitors.
Short-Circuit Protection
The AAT3215 contains an internal short-circuit pro-
tection circuit that will trigger when the output load
current exceeds the internal threshold limit. Under
short-circuit conditions, the output of the LDO reg-
ulator will be current limited until the short-circuit
condition is removed from the output or LDO regu-
lator package power dissipation exceeds the
device thermal limit.
Ceramic Capacitor Materials: Ceramic capaci-
tors less than 0.1µF are typically made from NPO
or C0G materials. NPO and C0G materials gener-
ally have tight tolerance and are very stable over
temperature. Larger capacitor values are usually
composed of X7R, X5R, Z5U, or Y5V dielectric
materials. 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
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 temperature; this could cause problems for cir-
cuit operation. X7R and X5R dielectrics are much
more desirable. The temperature tolerance of X7R
dielectric is better than ±15%.
Thermal Protection
The AAT3215 has an internal thermal protection cir-
cuit which will turn on when the device die temper-
ature exceeds 150°C. The internal thermal protec-
tion 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
temperature falls back below the 150°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.
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 an equivalent material and capacitance
value. These larger devices can improve circuit tran-
sient response when compared to an equal value
capacitor in a smaller package size.
No-Load Stability
The AAT3215 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.
Consult capacitor vendor datasheets carefully
when selecting capacitors for LDO regulators.
Enable Function
The AAT3215 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 2.0V. The LDO regulator will
go into the disable shutdown mode when the volt-
Reverse Output-to-Input Voltage
Conditions and Protection
Under normal operating conditions, a parasitic
diode exists between the output and input of the
LDO regulator. The input voltage should always
remain greater than the output load voltage, main-
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3215.2006.05.1.6
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
