AAT2503
Adjustable 3-Channel Regulator
POK Output
No-Load Stability
LDOA of the AAT2503 features an integrated
Power OK comparator which can be used as an
error flag. The POK open drain output goes low
when output voltage is 6ꢀ (typ) below its nominal
regulation voltage. Additionally, any time LDOA is
in shutdown, the POK output is pulled low. Connect
a pull-up resistor from POK to OUTA.
The LDOs in the AAT2503 are designed to main-
tain output voltage regulation and stability under
operational no-load conditions. This is an important
characteristic for applications where the output cur-
rent may drop to zero.
Reverse Output-to-Input Voltage
Conditions and Protection
Enable Function
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.
The AAT2503 features an LDO regulator enable/dis-
able function. Each LDO has its own dedicated
enable pin. These pins (ENA, ENB) are active high
and are compatible with CMOS logic. To assure the
LDO regulators will switch on, ENA/B must be
greater than 1.4V. The LDO regulators will shut
down when the voltage on the ENA/B pins falls
below 0.6V. In shutdown, the LDO regulators will
consume less than 1.0µA of current. 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.
Short-Circuit Protection
The AAT2503 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-
tion is removed from the output or LDO regulator
package power dissipation exceeds the device
thermal limit.
Thermal Considerations and High
Output Current Applications
The LDOs of the AAT2503 are designed to deliver
continuous output load currents of 150mA each
under normal operation. This is desirable for circuit
applications where there might be a brief high in-
rush current during a power-on event.
Thermal Protection
Each of the two LDOs of the AAT2503 has an inter-
nal thermal protection circuit which will turn on when
the device die temperature exceeds 140°C. The
LDO regulator outputs will remain in a shutdown
state until the internal die temperature falls back
below the ~125°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.
The limiting characteristic for the maximum output
load current 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.
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2503.2007.04.1.1
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
