AAT1149 Datasheet, PDF (10/20 Pages) Advanced Analogic Technologies – 3MHz Fast Transient 400mA Step-Down Converter

Functional Block Diagram
FB
AAT1149
3MHz Fast Transient
400mA Step-Down Converter
IN
Err
Am. p
Voltage
Reference
EN
INPUT
DH
Logic
DL
LX
PGND
AGND
Functional Description
The AAT1149 is a high performance 400mA 3.0MHz
monolithic step-down converter. It minimizes exter-
nal component size, enabling the use of a tiny 0603
inductor that is only 1mm tall, and optimizes effi-
ciency 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).
Only three external power components (C_IN, C_OUT,
and L) are required. Output voltage is programmed
with external feedback resistors, ranging from 1.0V
to the input voltage. An additional feed-forward
capacitor can also be added to the external feed-
back to provide improved transient response (see
Figure 4).
At dropout, the converter duty cycle increases to
100% and the output voltage tracks the input volt-
age minus the R_DS(ON) 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.
10
1149.2006.11.1.0