SwitchReg
TM
AAT1155
1MHz 2.5A Step-Down DC/DC Converter
1155.2005.11.1.6
1
General Description
The AAT1155 SwitchRegTM is a member of
AnalogicTech's Total Power Management ICTM
(TPMICTM) product family. The step-down switch-
ing converter is ideal for applications where high
efficiency, small size, and low ripple are critical.
Able to deliver 2.5A with an internal power MOS-
FET, the current-mode controlled IC provides high
efficiency. Fully internally compensated, the
AAT1155 simplifies system design and lowers
external parts count.
The AAT1155 is available in a Pb-free MSOP-8
package and is rated over the -40C to +85C tem-
perature range.
Features
5.5V Max Supply Input
Fixed or Adjustable V
OUT
: 1.0V to 4.2V
2.5A Output Current
Up to 95% Efficiency
Integrated Low On Resistance Power
Switches
Internally Compensated Current Mode Control
1MHz Switching Frequency
Constant PWM Mode
Low Output Ripple With Light Load
Internal Soft Start
Current Limit Protection
Over-Temperature Protection
MSOP-8 Package
-40C to +85C Temperature Range
Applications
Cable/DSL Modems
Computer Peripherals
High Efficiency Conversion from 5V or 3.3V
Supply
Network Cards
Set-Top Boxes
Typical Application
OUTPUT
1.5
H
120
F
LX
LX
VP
FB
GND
AAT1155
VCC
ENABLE
10
F
0.1
F
100
INPUT
AAT1155
1MHz 2.5A Step-Down DC/DC Converter
2
1155.2005.11.1.6
Pin Descriptions
Pin Configuration
MSOP-8
1
2
LX
VP
LX
VP
FB
GND
EN
VCC
1
2
3
4
8
7
6
5
Pin #
Symbol
Function
1
FB
Feedback input pin.
2
GND
Signal ground.
3
EN
Converter enable pin.
4
VCC
Small signal filtered bias supply.
5, 8
VP
Input supply for converter power stage.
6, 7
LX
Inductor connection pin.
AAT1155
1MHz 2.5A Step-Down DC/DC Converter
1155.2005.11.1.6
3
Absolute Maximum Ratings
1
T
A
= 25C, unless otherwise noted.
Thermal Characteristics
3
Recommended Operating Conditions
Symbol
Description
Rating
Units
T
Ambient Temperature Range
-40 to +85
C
Symbol
Description
Value
Units
JA
Maximum Thermal Resistance
150
C/W
P
D
Maximum Power Dissipation
833
mW
Symbol
Description
Value
Units
V
CC
, V
P
V
CC
, V
P
to GND
6
V
V
LX
LX to GND
-0.3 to V
P
+0.3
V
V
FB
FB to GND
-0.3 to V
CC
+0.3
V
V
EN
EN to GND
-0.3 to V
CC
+0.3
V
T
J
Operating Junction Temperature Range
-40 to 150
C
T
LEAD
Maximum Soldering Temperature (at leads, 10 sec)
300
C
V
ESD
ESD Rating
2
- HBM
3000
V
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at condi-
tions other than the operating conditions specified is not implied. Only one Absolute Maximum Rating should be applied at any one time.
2. Human body model is a 100pF capacitor discharged through a 1.5k
resistor into each pin.
3. Mounted on a demo board (FR4, in still air).
Electrical Characteristics
V
IN
= V
CC
= V
P
= 5V, T
A
= -40C to +85C, unless otherwise noted. Typical values are T
A
= 25C.
Symbol
Description
Conditions
Min Typ Max Units
V
IN
Input Voltage Range
2.7
5.5
V
V
OUT
Output Voltage Tolerance
V
IN
= V
OUT
+ 0.2 to 5.5V,
-2.5
2.5
%
I
OUT
= 0.5A
V
IL
Input Low Voltage
0.6
V
V
IH
Input High Voltage
1.4
V
V
UVLO
Under-Voltage Lockout
V
IN
Rising
2.5
V
V
IN
Falling
1.2
V
UVLO(HYS)
Under-Voltage Lockout Hysteresis
250
mV
I
Q
Quiescent Supply Current
No Load, V
FB
= 0V
630 1000
A
I
SHDN
Shutdown Current
V
EN
= 0V, V
IN
= 5.5V
1.0
A
I
LIM
Current Limit
T
A
= 25C
4.4
A
R
DS(ON)L
High Side Switch On Resistance
T
A
= 25C
60
m
Efficiency
I
OUT
= 1.0A
92
%
V
OUT
(V
OUT
*
V
IN
) Load Regulation
I
LOAD
= 0A to 2.5A
2.3
%
V
OUT
/V
OUT
Line Regulation
V
IN
= 2.7V to 5.5V
0.75
%/V
F
OSC
Oscillator Frequency
T
A
= 25C
1
MHz
T
SD
Over-Temperature Shutdown
140
C
Threshold
T
HYS
Over-Temperature Shutdown
15
C
Hysteresis
AAT1155
1MHz 2.5A Step-Down DC/DC Converter
4
1155.2005.11.1.6
Typical Characteristics
Output Voltage Variation vs. Temperature
(I
OUT
= 2A; V
O
= 3.3V)
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
-20
0
20
40
60
80
100
Temperature (
C)
Variation (%)
Enable Threshold vs. Input Voltage
0.6
0.7
0.8
0.9
1
1.1
1.2
2.5
3
3.5
4
4.5
5
5.5
Input Voltage (V)
Enable Threshold (V)
EN(H)
EN(L)
Oscillator Frequency Variation vs. Temperature
(V
IN
= 5V)
-4
-3
-2
-1
0
1
-20
0
20
40
60
80
100
Temperature (
C)
Variation (%)
R
DS(ON)
vs. Input Voltage
(I
DS
= 1A)
40
45
50
55
60
65
70
75
80
2.5
3
3.5
4
4.5
5
5.5
Input Voltage (V)
R
DS(ON)
(m
)
Oscillator Frequency Variation
vs. Input Voltage
(V
OUT
= 3.3V)
-0.5
-0.25
0
0.25
0.5
3.5
4
4.5
5
5.5
Input Voltage (V)
Variation (%)
R
DS(ON)
vs. Temperature
40
50
60
70
80
90
-20
0
20
40
60
80
100
120
Temperature (
C)
R
DS(ON)
(m
)
2.7V
3.6V
4.2V
5.0V
5.5V
AAT1155
1MHz 2.5A Step-Down DC/DC Converter
1155.2005.11.1.6
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