1MHz 2.5A Step-Down DC/DC Converter
General Description
The AAT1155 SwitchReg is a step-down switching
converter ideal for applications where high efficien-
cy, small size, and low ripple are critical. Able to
deliver 2.5A with an internal power MOSFET, the
current-mode controlled IC provides high efficien-
cy. Fully internally compensated, the AAT1155 sim-
plifies system design and lowers external parts
count.
The AAT1155 is available in a Pb-free MSOP-8
package and is rated over the -40°C to +85°C tem-
perature range.
AAT1155
Features
•
•
•
•
•
•
•
•
•
•
•
•
•
•
SwitchReg
™
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 Pulse Width Modulation (PWM)
Mode
Low Output Ripple with Light Load
Internal Soft Start
Current Limit Protection
Over-Temperature Protection
MSOP-8 Package
-40°C to +85°C Temperature Range
Applications
•
•
•
•
•
Cable/DSL Modems
Computer Peripherals
High Efficiency Conversion from 5V or 3.3V
Supply
Network Cards
Set-Top Boxes
Typical Application
INPUT
10μF
VP
FB
AAT1155
EN
100Ω
VCC
LX
LX
1.5μH
OUTPUT
GND
0.1μF
120μF
1155.2006.09.1.7
1
1MHz 2.5A Step-Down DC/DC Converter
Pin Descriptions
Pin #
1
2
3
4
5, 8
6, 7
AAT1155
Symbol
FB
GND
EN
VCC
VP
LX
Function
Feedback input pin.
Signal ground.
Converter enable pin.
Small signal filtered bias supply.
Input supply for converter power stage.
Inductor connection pin.
Pin Configuration
MSOP-8
FB
GND
EN
VCC
1
8
VP
LX
LX
VP
1
2
2
7
3
6
4
5
2
1155.2006.09.1.7
1MHz 2.5A Step-Down DC/DC Converter
Absolute Maximum Ratings
1
T
A
= 25°C, unless otherwise noted.
Symbol
V
CC
, V
P
V
LX
V
FB
V
EN
T
J
T
LEAD
V
ESD
AAT1155
Description
VCC, VP to GND
LX to GND
FB to GND
EN to GND
Operating Junction Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
ESD Rating
2
- HBM
Value
6
-0.3 to V
P
+0.3
-0.3 to V
CC
+0.3
-0.3 to V
CC
+0.3
-40 to 150
300
3000
Units
V
V
V
V
°C
°C
V
Thermal Characteristics
3
Symbol
Θ
JA
P
D
Description
Maximum Thermal Resistance
Maximum Power Dissipation
Value
150
833
Units
°C/W
mW
Recommended Operating Conditions
Symbol
T
Description
Ambient Temperature Range
Rating
-40 to +85
Units
°C
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 1.5kΩ resistor into each pin.
3. Mounted on a demo board (FR4, in still air).
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3
1MHz 2.5A Step-Down DC/DC Converter
Electrical Characteristics
V
IN
= V
CC
= V
P
= 5V, T
A
= -40°C to +85°C, unless otherwise noted. Typical values are T
A
= 25°C.
Symbol
V
IN
V
OUT
V
IL
V
IH
V
UVLO
V
UVLO(HYS)
I
Q
I
SHDN
I
LIM
R
DS(ON)H
η
ΔV
OUT
(V
OUT
*ΔV
IN
)
ΔV
OUT
/V
OUT
F
OSC
T
SD
T
HYS
AAT1155
Description
Input Voltage Range
Output Voltage Tolerance
Input Low Voltage
Input High Voltage
Under-Voltage Lockout
Under-Voltage Lockout Hysteresis
Quiescent Supply Current
Shutdown Current
Current Limit
High Side Switch On Resistance
Efficiency
Load Regulation
Line Regulation
Oscillator Frequency
Over-Temperature Shutdown
Threshold
Over-Temperature Shutdown
Hysteresis
Conditions
V
IN
= V
OUT
+ 0.2 to 5.5V,
I
OUT
= 0.5A
Min Typ Max Units
2.7
-2.5
5.5
2.5
0.6
1.4
V
%
V
V
V
V
IN
Rising
V
IN
Falling
No Load, V
FB
= 0V
V
EN
= 0V, V
IN
= 5.5V
T
A
= 25°C
T
A
= 25°C
I
OUT
= 1.0A
I
LOAD
= 0A to 2.5A
V
IN
= 2.7V to 5.5V
T
A
= 25°C
2.5
1.2
250
630
4.4
mV
1000 µA
1.0
µA
A
60
mΩ
92
%
±2.3
%
0.75
%/V
1
MHz
140
°C
15
°C
4
1155.2006.09.1.7
1MHz 2.5A Step-Down DC/DC Converter
Typical Characteristics
Efficiency vs. Load Current
(V
IN
= 5.0V; V
OUT
= 3.3V)
100
95
90
80
AAT1155
R
DS(ON)
vs. Temperature
2.7V
3.6V
4.2V
Efficiency (%)
R
DS(ON)
(mΩ)
90
85
80
75
70
65
60
0.01
0.1
1
10
70
60
5.0V
50
40
-20
0
20
40
60
80
5.5V
100
120
Output Current (A)
Temperature (°C)
Oscillator Frequency Variation
vs. Input Voltage
(V
OUT
= 3.3V)
0.5
80
75
R
DS(ON)
vs. Input Voltage
(I
DS
= 1A)
Variation (%)
0.25
R
DS(ON)
(mΩ)
Ω
70
65
60
55
50
45
40
2.5
3
3.5
4
4.5
5
5.5
0
-0.25
-0.5
3.5
4
4.5
5
5.5
Input Voltage (V)
Input Voltage (V)
Oscillator Frequency Variation vs. Temperature
(V
IN
= 5V)
1
1.2
Enable Threshold vs. Input Voltage
Enable Threshold (V)
1.1
1
0.9
0.8
0.7
0.6
0
EN(H)
Variation (%)
-1
-2
-3
-4
-20
0
20
40
60
80
100
EN(L)
2.5
3
3.5
4
4.5
5
5.5
Temperature (°C)
Input Voltage (V)
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