PRODUCT DATASHEET
AAT1
149A
SwitchReg
TM
Functional Block Diagram
FB
IN
2.2MHz Fast Transient 400mA Step-Down Converter
Err
Amp
.
DH
Voltage
Reference
Logic
LX
EN
INPUT
DL
PGND
AGND
Functional Description
The AAT1149A is a high performance 400mA 2.2MHz
monolithic step-down converter. It minimizes external
component size, enabling the use of a tiny 0603 inductor
that is only 1mm tall, and is optimized for low noise.
Apart from the small bypass input capacitor, only a small
L-C filter is required at the output. Typically, a 1.8μH
inductor and a 4.7μF ceramic capacitor are recommend-
ed (see table of values).
Only three external power components (C
IN
, C
OUT
, and L)
are required. Output voltage is fixed internally.
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 2.2V to 5.5V. The converter
efficiency has been optimized for all load conditions,
ranging from no load to 400mA.
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.
8
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1149A.2008.08.1.1
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