AAT2504
Adjustable 3-Channel Regulator
Functional Block Diagram
FB
VIN
VP
Voltage
Reference
DH
Err.
Amp.
LX
MODE/SYNC
Logic
Control
Logic
DL
PGND
OUTA
EN
VLDOA
ENB
Over-Current
Protection
VLDOB
ENA
FBA
Err.
Amp.
Voltage
Reference
90%
VREF
POK
OUTB
AGND
FBB
operation maintains high efficiency under light load
conditions (typically <50mA) when MODE/SYNC is
grounded. The MODE/SYNC pin tied high allows
optional "PWM Only" operation. This maintains con-
stant frequency and low output ripple across all load
conditions. Alternatively, by connecting an external
clock to the AAT2504's MODE/SYNC pin, the inter-
nal clock is disabled. The external synchronization
must stay between 1MHz and 3MHz.
Functional Description
The AAT2504 is a high performance power man-
agement IC comprised of a step-down converter
and two linear regulators. The step-down convert-
er operates in both fixed and variable frequency
modes for high efficiency performance. The switch-
ing frequency is 2MHz, minimizing the size of the
inductor. The converter requires only three external
power components (CIN, COUT, and L). Each LDO
can deliver up to 300mA. Each regulator has inde-
pendent input voltage and enable pins and oper-
ates with ceramic capacitors.
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
compensation signal is added to the sensed current
to maintain 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.
Switch-Mode Step-Down Converter
The switching regulator is a monolithic step-down
converter operating with input voltage range of 2.7V
to 5.5V. Power devices are sized for 800mA current
capability and achieves over 95% efficiency. The
internal oscillator operates at 2MHz, minimizing the
cost and size of external components. Light Load
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-
2504.2007.06.1.0
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