AAT3242
300mA/150mA Dual CMOS LDO Linear Regulator
of X7R dielectric is better than ±15%. Capacitor
tion is removed from the output or LDO regulator
package power dissipation exceeds the device
thermal limit.
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 an equivalent material and capacitance value.
These larger devices can improve circuit transient
response when compared to an equal value capac-
itor in a smaller package size. Consult capacitor
vendor datasheets carefully when selecting capac-
itors for LDO regulators.
Thermal Protection
The AAT3242 has an internal thermal protection cir-
cuit which will turn on when the device die temper-
ature exceeds 145°C. The LDO regulator output will
remain in a shutdown state until the internal die
temperature falls back below the 145°C trip point.
The combination and interaction between the short-
circuit and thermal protection systems allows the
LDO regulators to withstand indefinite short-circuit
conditions without sustaining permanent damage.
POK Output
The AAT3242 features integrated Power OK com-
parators which can be used as an error flag. The
POK open drain output goes low when output volt-
age is 6% (typ) below its nominal regulation volt-
age. Additionally, any time one of the regulators is
in shutdown, the respective POK output is pulled
low. Connect a pull-up resistor from POKA to
OUTA, and POKB to OUTB.
No-Load Stability
The AAT3242 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.
Enable Function
The AAT3242 features an LDO regulator enable/dis-
able function. Each LDO has its own dedicated
enable pin. These pins (EN) are active high and are
compatible with CMOS logic. To assure the LDO
regulators will switch on, ENA/B must be greater
than 1.6V. The LDO regulators will shut down when
the voltage on the ENA/B pins falls below 0.6V. In
shutdown, the AAT3242 will consume less than
1.0µA of current. If the enable function is not need-
ed in a specific application, it may be tied to VIN to
keep the LDO regulator in a continuously on state.
Reverse Output-to-Input Voltage
Conditions and Protection
Under normal operating conditions, a parasitic diode
exists between the output and input of the LDO reg-
ulator. The input voltage should always remain
greater than the output load voltage maintaining a
reverse bias on the internal parasitic diode.
Conditions where VOUT might exceed VIN should be
avoided since this would forward bias the internal
parasitic diode and allow excessive current flow into
the VOUT pin, possibly damaging the LDO regulator.
In applications where there is a possibility of VOUT
exceeding VIN for brief amounts of time during nor-
mal operation, the use of a larger value CIN capaci-
tor is highly recommended. A larger value of CIN with
respect to COUT will effect a slower CIN decay rate
during shutdown, thus preventing VOUT from
exceeding VIN. In applications where there is a
greater danger of VOUT exceeding VIN for extended
periods of time, it is recommended to place a
Schottky diode across VIN to VOUT (connecting the
cathode to VIN and anode to VOUT). The Schottky
diode forward voltage should be less than 0.45V.
When the LDO regulators are in shutdown mode,
an internal 20Ω resistor is connected between
VOUT and GND. This is intended to discharge COUT
when the LDO regulators are disabled. The internal
20Ω has no adverse effects on device turn-on time.
Short-Circuit Protection
The AAT3242 contains internal short-circuit protec-
tion that will trigger when the output load current
exceeds the internal threshold limit. Under short-
circuit conditions, the output of the LDO regulator
will be current limited until the short-circuit condi-
3242.2006.04.1.10
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AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
