PRODUCT DATASHEET
AAT1149
SwitchRegTM
3MHz FastTransient 400mA Step-Down Converter
Functional Block Diagram
IN
FB
Err
Amp
.
DH
LX
Voltage
Logic
Reference
DL
INPUT
EN
PGND
AGND
added to the external feedback to provide improved
transient response (see Figure 4).
Functional Description
The AAT1149 is a high performance 400mA 3.0MHz
monolithic step-down converter. It minimizes external
component size, enabling the use of a tiny 0603 inductor
that is only 1mm tall, and optimizes efficiency over the
complete load range. 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 recommended (see table of values).
At dropout, the converter duty cycle increases to 100%
and the output voltage tracks the input voltage minus
the RDS(ON) drop of the P-channel high-side MOSFET.
The input voltage range is 2.7V 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.
Only three external power components (CIN, COUT, and L)
are required. Output voltage is programmed with exter-
nal feedback resistors, ranging from 1.0V to the input
voltage. An additional feed-forward capacitor can also be
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