PRODUCT DATASHEET
AAT1276
SwitchRegTM
Boost Converter with USB Power Switch
Functional Block Diagram
LIN
SW
OUT1
IN
Boost Regulator Control
VCC
FB
EN
OUT2
Load Switch Control
SET
FLT
GND
open-drain fault reporting signal (FLT). The fault report-
ing signal has a 4ms turn-on delay.
Functional Description
The AAT1276 is a 500mA synchronous boost converter
with a current-limited load switch targeted for single-cell
Lithium-ion/polymer devices acting as a portable host
for USB power.
Control Scheme
The control circuit uses hysteretic current mode control
with internal inductor current sensing for very high effi-
ciency over a wide output current range. For heavy load,
the boost converter operates in continuous conduction
mode (CCM). This minimizes the RMS current and opti-
mizes the efficiency at load conditions where the losses
are dominated by the power MOSFET RDS(ON). This also
keeps the ripple current to a minimum and minimizes
the output voltage ripple and the output capacitor size.
A zero current comparator senses the inductor current
and prevents reverse current flow for optimum light load
efficiency.
The AAT1276 has integrated control and synchronous
MOSFETs, minimizing the cost and the number of exter-
nal components. Additional features include a soft-start
function which allows the load voltage to ramp up in a
controlled manner, eliminating output voltage overshoot
and minimizing inrush current. Typical soft-start time
for the boost converter is approximately 300μs.
The AAT1276 also has a load switch with user-program-
mable current limiting. The load switch reports over-
current and over-temperature conditions through an
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ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
