AAT2749 Datasheet, PDF (9/17 Pages) Skyworks Solutions Inc. – 3.0MHz Step-Down Converter and Low-V in LDO

Functional Block Diagram
IN_BUCK
CE
MODE
Control
DATA SHEET
AAT2749
3.0MHz Step-Down Converter and Low-V_IN LDO
VP
EN _DC-DC
REF ^Converter
VP EN
REF LDO
GND
LX
GND
OUT_BUCK
IN_LDO
OUT_LDO
Functional Description
The AAT2749 is a two channel power converter that
operates from a 2.3V to 5.5V power supply. The AAT2749
step-down converters can deliver up to 600mA while the
LDO regulator can deliver up to 300mA. The typical no
load quiescent current is 100μA for both the step-down
converter and LDO regulator.
Step-Down Regulator
The AAT2749 contains a high performance 600mA,
3.0MHz monolithic step-down converter. Typically, a
2.2μH inductor and a 4.7μF ceramic capacitor are recom-
mended (see table of values).
At dropout, the converter duty cycle increases to 100%
and the output voltage tracks the input voltage minus
the R_DS(ON) drop of the P-channel high-side MOSFET. The
input voltage range is 2.3V to 5.5V. The converter effi-
ciency has been optimized for all load conditions, ranging
from no load to 600mA.
The internal error amplifier and compensation provides
excellent transient response, load, and line regulation.
Soft start eliminates any output voltage overshoot when
the enable or the input voltage is applied.
Mode Pin
To ensure high efficiency across the load range, the
AAT2749 will automatically shift out of PWM mode in
light load conditions. This mode of operation maintains
high efficiency under light load conditions (typically
<150mA). The MODE pin allows optional fixed frequency
PWM mode for improved noise performance. This main-
tains constant frequency and low output ripple across all
load conditions.
Control Loop
The AAT2749 step down converter is 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.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
202037A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012
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