AAT1153 Datasheet, PDF (9/19 Pages) Advanced Analogic Technologies – 2A Step-Down Converter

Functional Block Diagram
DATA SHEET
AAT1153
2A Step-Down Converter
FB/OUT
EN
0.6V Softstart
OSC
I
COMP
SLOPE
COMP
SET
ISENSE
AMP
RESET
PWM
LOGIC
NON-OVERLAP
CONTROL
Over-Temperature
and Short-Circuit
Protection
R1*
OVDET
0.65V
R2*
0.6V
REF
SHUTDOWN
IZERO
COMP
IN
V_IN 2.5V to 5.5V
LX
L1
C_OUT
PGND
V_OUT
R1*
R2*
AIN AGND
*The resistor divider R1 + R2 is internally set for the fixed output versions, and is externally set for the adjustable output versions.
Functional Description
The AAT1153 is a high output current monolithic switch-
mode step-down DC-DC converter. The device operates
at a fixed 1.2MHz switching frequency, and uses a slope
compensated current mode architecture. This step-down
DC-DC converter can supply up to 2A output current at
V_IN = 3V and has an input voltage range from 2.5V to
5.5V. It minimizes external component size and opti-
mizes efficiency at the heavy load range. The slope com-
pensation allows the device to remain stable over a
wider range of inductor values so that smaller values
(1μH to 4.7μH) with lower DCR can be used to achieve
higher efficiency. Apart from the small bypass input
capacitor, only a small L-C filter is required at the output.
The device can be programmed with external feedback
to any voltage, ranging from 0.6V to near the input volt-
age. It uses internal MOSFETs to achieve high efficiency
and can generate very low output voltages by using an
internal reference of 0.6V. At dropout, the converter duty
cycle increases to 100% and the output voltage tracks
the input voltage minus the low R_DS(ON) drop of the
P-channel high-side MOSFET and the inductor DCR. The
internal error amplifier and compensation provides
excellent transient response, load and line regulation.
Internal soft start eliminates any output voltage over-
shoot when the enable or the input voltage is applied.
Current Mode PWM Control
Slope compensated current mode PWM control provides
stable switching and cycle-by-cycle current limit for
excellent load and line response with protection of the
internal main switch (P-channel MOSFET) and synchro-
nous rectifier (N-channel MOSFET). During normal
operation, the internal P-channel MOSFET is turned on
for a specified time to ramp the inductor current at each
rising edge of the internal oscillator, and switched off
when the peak inductor current is above the error volt-
age. The current comparator, I_COMP, limits the peak induc-
tor current. When the main switch is off, the synchro-
nous rectifier turns on immediately and stays on until
either the inductor current starts to reverse, as indicated
by the current reversal comparator, I_ZERO, or the begin-
ning of the next clock cycle.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
201992B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
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