AAT2148 Datasheet, PDF (9/18 Pages) Skyworks Solutions Inc. – Low-Noise, Fast Transient 1A Step-Down Converter

Functional Block Diagram
DATA SHEET
AAT2148
Low-Noise, Fast Transient 1A Step-Down Converter
VCC
VP
0.6V REF
FB
OP. AMP
CMP
DH
LOGIC
1MΩ
DL
Temp.
Sensing
OSC
PGND
EN
LX
PGND
Functional Description
The AAT2148 is a high performance 1A 2MHz mono-
lithic step-down converter. It has been designed with
the goal of minimizing external component size and
optimizing efficiency over the complete load range, and
produces reduced ripple and spectral noise. 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).
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_DSON 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 1A.
The internal error amplifier and compensation provides
excellent transient response, load, and line regulation.
Soft start eliminates any output voltage overshoot and
input inrush current when the enable or the input volt-
age is applied.
Control Loop
The AAT2148 is a peak current mode step-down con-
verter. The current through the P-channel MOSFET (high
side) is sensed for current loop control, as well as short
circuit and overload protection. A fixed slope compensa-
tion signal is added to the sensed current to maintain
stability for duty cycles greater than 50%. The peak cur-
rent mode loop appears as a voltage-programmed cur-
rent source in parallel with the output capacitor.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
202009A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
9