PRODUCT DATASHEET
AAT1
161
SwitchReg
TM
Functional Block Diagram
LDO
Internal
Power
Current
Sense Amp
AIN
IN
13.2V Input, 3A Step-Down Converter
FB
*
LDO
Err
Amp
Voltage
Reference
Comp
DH
Control
Logic
LX
PGND
EN
Input
DGND
AGND
COMP
* For fixed output voltage versions, FB is connected to the error amplifier through the resistive voltage divider shown.
Functional Description
The AAT1161 is a current-mode step-down DC/DC con-
verter that operates over a wide 4V to 13.2V input voltage
range and is capable of supplying up to 3A to the load
with the output voltage regulated as low as 0.6V. The
P-channel power switch is internal, reducing the number
of external components required. An external Schottky
diode is used for the low side rectifier. The output voltage
is adjusted by an external resistor divider; fixed output
voltage versions are available upon request. The regula-
tion system is externally compensated, allowing the cir-
cuit to be optimized for each application. The AAT1161
includes cycle-by-cycle current limiting, frequency fold-
back for improved short-circuit performance, and thermal
overload protection to prevent damage in the event of an
external fault condition.
Control Loop
The AAT1161 regulates the output voltage using con-
stant frequency current mode control. The AAT1161
monitors current through the high-side P-channel
MOSFET and uses that signal to regulate the output volt-
age. This provides improved transient response and
eases compensation. Internal slope compensation is
included to ensure the current “inside loop” stability.
High efficiency is maintained under light load conditions
by automatically switching to variable frequency Light
Load control. In this condition, transition losses are
reduced by operating at a lower frequency at light loads.
The AAT1161 uses an external Schottky rectifier diode to
minimize cost.
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