AAT1112
1.5A, 1.4MHz Step-Down Converter
Functional Block Diagram
VP
FB
VIN
Err.
Amp
DH
VREF
LX
Logic
EN
Input
DL
MODE/SYNC
PGND
GND
during 100% duty cycle operation. This is advan-
tageous in applications requiring high output volt-
ages (typically > 2.5V) at low input voltages.
Functional Description
The AAT1112 is a high performance 1.5A monolith-
ic step-down converter operating at 1.4MHz switch-
ing frequency. It minimizes external component
size and optimizes efficiency 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 3.3µH inductor and a 22µF
ceramic capacitor are recommended for a 3.3V
output (see table of recommended values).
The integrated low-loss MOSFET switches can
provide greater than 95% efficiency at full load.
PFM operation maintains high efficiency under light
load conditions (typically <150mA). The MODE/
SYNC pin allows optional "PWM only" mode. This
maintains constant frequency and low output ripple
across all load conditions. Alternatively, the IC can
be synchronized to an external clock via the
MODE/ SYNC input. External synchronization is
maintained between 0.6MHz and 3.0MHz.
At dropout, the converter duty cycle increases to
100% and the output voltage tracks the input volt-
age minus the RDS(ON) drop of the P-channel high-
side MOSFET (plus the DC drop of the external
inductor). The device integrates extremely low
RDS(ON) MOSFETs to achieve low dropout voltage
In battery-powered applications, as VIN decreases,
the converter dynamically adjusts the operating fre-
quency prior to dropout to maintain the required duty
cycle and provide accurate output regulation.
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1112.2007.01.1.1
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
