PRODUCT DATASHEET
AAT1157
SwitchReg
TM
General Description
The AAT1157 SwitchReg™ is a step-down switching con-
verter, ideal for applications where fixed frequency and
low ripple are required over the full range of load condi-
tions. The 2.7V to 5.5V input voltage range makes the
AAT1157 ideal for single-cell lithium-ion/polymer battery
applications. Capable of up to 1.2A with internal
MOSFETs, the current-mode controlled IC provides high
efficiency over a wide operating range. Fully integrated
compensation simplifies system design and lowers exter-
nal parts count. The device operates at a fixed 1MHz
switching frequency across all load conditions.
The AAT1157 is available in the Pb-free, 16-pin 3x3mm
QFN package and is rated over the -40°C to +85°C tem-
perature range.
1MHz 1.2A Buck DC/DC Converter
Features
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V
IN
Range: 2.7V to 5.5V
Up to 95% Efficiency
110 mΩ R
DS(ON)
Internal Switches
<1μA Shutdown Current
1MHz Buck Switching Frequency
Fixed or Adjustable V
OUT
≥
0.8V
Integrated Power Switches
Current Mode Operation
Internal Compensation
Stable with Ceramic Capacitors
Constant PWM Operation for Low Output Ripple
Internal Soft Start
Over-Temperature Protection
Current Limit Protection
16-Pin QFN 3x3mm Package
-40°C to +85°C Temperature Range
Applications
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HDD MP3 Players
Notebook Computers
PDAs
Point-of-Load Regulation
Set Top Boxes
Smart Phones
Wireless Notebook Adapters
Typical Application
3.3V
12
11
10
7
9
6
U1
AAT1157
VP
VP
VP
EN
VCC
N/C
N/C
FB
LX
LX
LX
N/C
PGND
PGND
4
15
14
13
16
3
2
1
2.5V
R3
187k
L1
3.0μH
R1
100
C1
10μF
R4
59k
C3-C4
2x 22μF
C2
0.1μF
8
5
SGND PGND
1157.2009.04.1.6
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