PRODUCT DATASHEET
AAT2503178
SystemPowerTM
Adjustable 3-Channel Regulator
tained between 1MHz and 3MHz. It consumes 30μA of
typical no load quiescent current, making it also ideal for
light load applications. The oscillator operates at 2MHz,
minimizing the cost and size of external components.
Soft Start / Enable
Soft start limits the current surge seen at the input and
eliminates output voltage overshoot in the step-down
converter.
A logic low on the EN pin shuts the converter down and
makes it consume less than 1μA of current.
The step-down converter and the two LDOs have inde-
pendent 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 during shutdown is less than 1μA.
Soft start increases the inductor current limit point in
discrete steps when the input voltage or enable input is
applied. It limits the current surge seen at the input and
eliminates output voltage overshoot.
Linear Regulators
For overload conditions, the peak input current is limit-
ed. As load impedance decreases and the output voltage
falls closer to zero, more power gets internally dissipat-
ed, raising the device temperature. 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 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 feed-
back pin for each LDO allows programming the output
voltage from VIN to 0.6V. The regulators have thermal
protection in case of adverse operating conditions.
LDOA features an integrated Power-OK comparator
which indicates when the output is out of regulation. The
POK is an open drain output and it is held low when the
AAT2503 is in shutdown mode.
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 protection. A fixed slope com-
pensation signal is added to the sensed current to main-
tain stability for duty cycles greater than 50%. The peak
current mode loop appears as a voltage-programmed
current source in parallel with the output capacitor.
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.
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 compensation terminates the
transconductance voltage error amplifier output. For
fixed voltage versions, the error amplifier reference volt-
age is internally set to program the converter output
voltage. For the adjustable output, the error amplifier
reference is fixed at 0.9V.
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 hys-
teresis. Once an over-temperature or over-current fault
conditions is removed, the output voltage automatically
recovers.
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ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
