AAT1123 Datasheet, PDF (8/20 Pages) Advanced Analogic Technologies – 1MHz Step-Down Converter

Functional Block Diagram
OUT
AAT1123
1MHz Step-Down Converter
VIN
See note
Err
Am. p
Voltage
Reference
EN
INPUT
DH
Logic
DL
LX
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.
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1123.2006.05.1.5