PRODUCT DATASHEET
AAT1140
SwitchReg
TM
Functional Block Diagram
OUT
IN
Fast Transient 600mA Step-Down Converter
See note
Err
Amp
.
DH
Voltage
Reference
Logic
LX
EN
INPUT
DL
GND
Note: For adjustable version, the internal feedback divider is omitted and the OUT pin is tied directly
to the internal error amplifier.
Functional Description
The AAT1140 is a high performance 600mA 1.4MHz
monolithic step-down converter. It has been designed
with the goal of minimizing external component size and
optimizing 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 4.7μH
inductor and a 4.7μF ceramic capacitor are recommend-
ed (see table of values).
The fixed output version requires only three external
power components (C
IN
, C
OUT
, and L). The adjustable ver-
sion can be programmed with external feedback to any
voltage, ranging from 0.6V to the input voltage. An addi-
tional feed-forward capacitor can also be added to the
external feedback to provide improved transient response
(see Figure 1).
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 2.7V to 5.5V. The converter
efficiency 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.
1140.2007.12.1.1
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