1MHz Step-Down Converter
Functional Block Diagram
OUT
VIN
AAT1123
See note
Err
Amp
.
DH
Voltage
Reference
Logic
LX
DL
EN
INPUT
PGND
AGND
Note: For adjustable version, the internal feedback divider is omitted and the FB pin is tied directly
to the internal error amplifier.
Functional Description
The AAT1123 is a high performance 600mA 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 out-
put. Typically, a 4.7µH inductor and a 22µF ceramic
capacitor are recommended (see Table of Values).
The fixed output version requires only three external
power components (C
IN
, C
OUT
, and L). The
adjustable version can be programmed with external
feedback to any voltage, ranging from 0.6V to the
input voltage. An additional feed-forward capacitor
can also be added to the external feedback to pro-
vide improved transient response (see Figure 1).
At dropout, the converter duty cycle increases to
100% and the output voltage tracks the input volt-
age minus the R
DSON
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 heavy load.
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.
8
1123.2006.05.1.5
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
