500mA Step-Down Converter
Functional Block Diagram
FB
VIN
VP
AAT1120
Err
Amp
DH
Voltage
Reference
Logic
LX
EN
INPUT
DL
PGND
GND
Functional Description
The AAT1120 is a high performance 500mA,
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.
The device is designed to operate with an output
voltage as low as 0.6V. Power devices are sized for
500mA current capability while maintaining over
90% efficiency at full load. Light load efficiency is
maintained at greater than 80% down to 1mA of
load current.
At dropout, the converter duty cycle increases to
100% and the output voltage tracks the input volt-
age minus the R
DS(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.
1120.2007.01.1.0
9
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
