AAT2503
Adjustable 3-Channel Regulator
For overload conditions, the peak input current is
limited. As load impedance decreases and the out-
put voltage falls closer to zero, more power gets
internally dissipated, raising the device tempera-
ture. Thermal protection completely disables
switching when internal dissipation becomes
excessive, protecting the device from damage.
The junction over-temperature threshold is 140°C
with 15°C of hysteresis.
The step-down converter and the two LDOs have
independent enable pins. When pulled low, the
enable input forces the LDO into shutdown mode
and forces the step-down converter into a low-
power, non-switching state. The input current dur-
ing shutdown is less than 1µA.
Linear Regulators
The two linear regulators are high performance
LDOs where each LDO can source up to 150mA of
current. For added flexibility, both regulators have
independent input voltages operating from 2.8V to
5.5V. An external feedback pin for each LDO allows
programming the output voltage from VIN to 0.6V.
The regulators have short-circuit and thermal pro-
tection in case of adverse operating conditions.
Control Loop
The AAT2503 includes a peak current mode step-
down converter. The current through the P-channel
MOSFET (high side) is sensed for current loop
control, as well as short-circuit and overload pro-
tection. A fixed slope compensation signal is added
to the sensed current to maintain stability for duty
cycles greater than 50ꢀ. The peak current mode
loop appears as a voltage-programmed current
source in parallel with the output capacitor.
LDOA features an integrated Power-OK compara-
tor which indicates when the output is out of regu-
lation. The POK is an open drain output and it is
held low when the AAT2503 is in shutdown mode.
The output of the voltage error amplifier programs
the current mode loop for the necessary peak
switch current to force a constant output voltage for
all load and line conditions. Internal loop compen-
sation terminates the transconductance voltage
error amplifier output. For fixed voltage versions,
the error amplifier reference voltage is internally set
to program the converter output voltage. For the
adjustable output, the error amplifier reference is
fixed at 0.9V.
Under-Voltage Lockout
Internal bias of all circuits is controlled via the VIN
pin. Under-voltage lockout guarantees sufficient
VIN bias and proper operation of all internal circuits
prior to activation.
Over-Temperature Protection
Thermal protection completely disables switching
when internal dissipation becomes excessive. The
junction over-temperature threshold is 140°C with
15°C of hysteresis. Once an over-temperature or
over-current fault conditions is removed, the output
voltage automatically recovers.
Soft Start / Enable
Soft start limits the current surge seen at the input
and eliminates output voltage overshoot in the
step-down converter.
2503.2007.04.1.1
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