AAT1276 Datasheet, PDF (9/18 Pages) Advanced Analogic Technologies – Boost Converter with USB Power Switch

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Functional Block Diagram
LIN
PRODUCT DATASHEET
AAT1276
Boost Converter with USB Power Switch
SW
IN
VCC
Boost Regulator Control
OUT1
EN
SET
FLT
Load Switch Control
FB
OUT2
GND
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.
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
open-drain fault reporting signal (FLT). The fault report-
ing signal has a 4ms turn-on delay.
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 R_DS(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.
1276.2007.11.1.1
www.analogictech.com
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