AAT1121
1.5MHz, 250mA Step-Down Converter
Functional Block Diagram
FB
VIN
VP
Err
Amp
DH
Voltage
Reference
LX
Logic
INPUT
EN
DL
PGND
GND
90% efficiency at full load. Light load efficiency is
maintained at greater than 80% down to 1mA of
load current.
Functional Description
The AAT1121 is a high performance 250mA,
1.5MHz monolithic step-down converter designed
to operate with an input voltage range of 2.7V to
5.5V. The converter operates at 1.5MHz, which
minimizes the size of external components. Typical
values are 3.3µH for the output inductor and 4.7µF
for the ceramic output capacitor.
At dropout, the converter duty cycle increases to
100% and the output voltage tracks the input volt-
age minus the RDS(ON) drop of the P-channel high-
side MOSFET.
A high-DC gain error amplifier with internal com-
pensation controls the output. It provides excellent
transient response and load/line regulation. Soft
start eliminates any output voltage overshoot when
the enable or the input voltage is applied.
The device is designed to operate with an output
voltage as low as 0.6V. Power devices are sized for
250mA current capability while maintaining over
1121.2007.03.1.2
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ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
