AAT1138 Datasheet, PDF (12/21 Pages) Skyworks Solutions Inc. – 2A Step-Down Converter with Adjustable Input Current Limit

DATA SHEET
AAT1138
2A Step-Down Converter with Adjustable Input Current Limit
Functional Block Diagram
SET
ENSYS
FB
ENBUCK
1.2V
Ref .
Current
Limit
VP
Load Switch
Control
EN
Current
Limit
600mV
Reference
VP
Step-Down
Converter
EN
SYSOUT
GND
SVIN
PVIN
SW
PGND
Functional Description
The AAT1138 is a high performance 2A 1.2MHz synchro-
nous step-down converter with a programmable current
limited P-channel load switch. It is designed with the
goal of high performance with precise input current con-
trol under up to 2A load pulse on the step-down con-
verter output.
The P-channel load switch is adopted to limit the system
input current. The current limit value is programmed by
external resistor between SET and GND. Its fast tran-
sient response time make it protect the system input
power ideally.
The 2A step-down converter employs internal error
amplifier and compensation. It provides excellent tran-
sient response, load and line regulation. Its output volt-
age is programmed by an external resistor divider from
0.6V to converter input voltage. Soft start eliminates any
output voltage overshoot when the enable or input volt-
age is applied. Dropout mode makes the converter
increase the switch duty cycle to 100% and the output
voltage tracks the input voltage minus the R_DS(ON) drop of
the P-channel high-side MOSFET of the converter.
The AAT1138's input voltage range is 2.5V to 5.5V. Two
independent enable pins control the load switch and
step-down converter separately. The converter efficiency
has been optimized for all load conditions, ranging from
no load to 2A.
Step-Down Converter Control Loop
The internal DC-DC converter of the AAT1138 is a peak
current mode synchronous step-down converter. The
current through the P-channel MOSFET (high side) is
sensed for current loop control, as well as short circuit
and overload protection. A slope compensation signal is
added to the sensed current to maintain stability for duty
cycles greater than 50%. The peak current mode loop
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
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201978B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013