AAT1143
1MHz 400mA Step-Down Converter
Functional Block Diagram
OUT
VIN
See note
Err
Amp
.
DH
LX
Voltage
Logic
Reference
DL
INPUT
EN
PGND
AGND
Note: For adjustable version, the internal feedback divider is omitted and the FB pin is tied directly
to the internal error amplifier.
input voltage. An additional feed-forward capacitor
can also be added to the external feedback to pro-
vide improved transient response (see Figure 1).
Functional Description
The AAT1143 is a high performance 400mA 1MHz
monolithic step-down converter. It has been
designed with the goal of minimizing external com-
ponent size and optimizing efficiency over the com-
plete 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 recommended (see table of
values).
At dropout, the converter duty cycle increases to
100% and the output voltage tracks the input volt-
age minus the RDSON drop of the P-channel high-
side MOSFET.
The input voltage range is 2.7V to 5.5V. The con-
verter efficiency has been optimized for all load
conditions, ranging from no load to 400mA.
The internal error amplifier and compensation pro-
vides excellent transient response, load, and line
regulation. Soft start eliminates any output voltage
overshoot when the enable or the input voltage is
applied.
The fixed output version requires only three external
power components (CIN, COUT, and L). The
adjustable version can be programmed with external
feedback to any voltage, ranging from 0.6V to the
8
1143.2005.09.1.7
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
