AAT1157
1MHz 1.2A Buck DC/DC Converter
1157.2005.11.1.4
1
SwitchReg
TM
General Description
The AAT1157 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 fixed
frequency and low ripple are required over the full
range of load conditions. 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 com-
pensation simplifies system design and lowers
external 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 -40C
to +85C temperature range.
Features
V
IN
Range: 2.7V to 5.5V
Up to 95% Efficiency
110 m
R
DS(ON)
Internal Switches
<1A 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
-40C to +85C Temperature Range
Applications
HDD MP3 Players
Notebook Computers
PDAs
Point-of-Load Regulation
Set Top Boxes
Smart Phones
Wireless Notebook Adapters
Typical Application
3.0
H
L1
2x 22
F
C3-C4
10
F
C1
100
R1
0.1
F
C2
2.5V
3.3V
187k
R3
59k
R4
LX
14
N/C
6
EN
7
VCC
9
VP
10
N/C
8
LX
13
PGND
3
VP
12
VP
11
FB
4
LX
15
PGND
2
PGND
1
SGND
5
N/C
16
AAT1157
U1
AAT1157
1MHz 1.2A Buck DC/DC Converter
2
1157.2005.11.1.4
Pin Descriptions
Pin Configuration
QFN33-16
(Top View)
VP
VP
VP
N/C
PGND
PGND
PGND
1
2
3
4
N/C
SGND
EN
16
15
14
13
5
6
7
8
12
11
10
9
N/C
VCC
LX
LX
LX
FB
Pin #
Symbol
Function
1, 2, 3
PGND
Main power ground return pin. Connect to the output and input capacitor
return. (See board layout rules.)
4
FB
Feedback input pin. This pin is connected to the converter output. It is used to
set the output of the converter to regulate to the desired value via an internal
resistive divider. For an adjustable output, an external resistive divider is con-
nected to this pin.
5
SGND
Signal ground. Connect the return of all small signal components to this pin.
(See board layout rules.)
7
EN
Enable input pin. A logic high enables the converter; a logic low forces the
AAT1157 into shutdown mode reducing the supply current to less than 1A.
The pin should not be left floating.
6, 8, 16
N/C
Not internally connected.
9
VCC
Bias supply. Supplies power for the internal circuitry. Connect to input power
via low pass filter with decoupling to SGND.
10, 11, 12
VP
Input supply voltage for the converter power stage. Must be closely decoupled
to PGND.
13, 14, 15
LX
Connect inductor to these pins. Switching node internally connected to the
drain of both high- and low-side MOSFETs.
EP
Exposed paddle (bottom); connect to PGND directly beneath package.
AAT1157
1MHz 1.2A Buck DC/DC Converter
1157.2005.11.1.4
3
Absolute Maximum Ratings
1
Thermal Characteristics
Recommended Operating Conditions
Symbol
Description
Value
Units
T
Ambient Temperature Range
-40 to 85
C
Symbol
Description
Value
Units
JA
Maximum Thermal Resistance (QFN33-16)
3
50
C/W
JC
Maximum Thermal Resistance (QFN33-16)
4.2
C/W
P
D
Maximum Power Dissipation (QFN33-16) (T
A
= 25C)
3, 4
2.0
W
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 -6
V
T
J
Operating Junction Temperature Range
-40 to150
C
V
ESD
ESD Rating
2
- HBM
3000
V
1. Stresses above those listed in Absolute Maximum Ratings may cause damage to the device. Functional operation at conditions 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 100pF capacitor discharged through a 1.5k
resistor into each pin.
3. Mounted on a demo board (FR4, in still air). Exposed pad must be mounted to PCB.
4. Derate 20mW/C above 25C.
AAT1157
1MHz 1.2A Buck DC/DC Converter
4
1157.2005.11.1.4
Electrical Characteristics
1
V
IN
= V
CC
= V
P
= 5V, T
A
= -40C to +85C, unless otherwise noted. Typical values are at 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,
-4
+4
%
I
OUT
= 0 to 1.2A
V
OUT
/V
OUT
Load Regulation
V
IN
= 4.2V, I
LOAD
= 0 to 1.2A
2.5
%
V
OUT
(V
OUT
*
V
IN
) Line Regulation
V
IN
=2.7 to 5.5V
0.1
%/V
I
Q
Quiescent Supply Current
No Load
160
300
A
I
SHDN
Shutdown Current
V
EN
= 0V, V
IN
= 5.5V
1.0
A
I
LIM
Current Limit
T
A
= 25C
1.7
A
V
UVLO
Under-Voltage Lockout
V
IN
Rising, V
EN
= V
CC
2.5
V
V
IN
Falling, V
EN
= V
CC
1.2
V
UVLO(HYS)
Under-Voltage Lockout Hysteresis
250
mV
V
IL
Input Low Voltage
0.6
V
V
IH
Input High Voltage
1.4
V
I
IL
Input Low Current
V
IN
= V
FB
= 5.5V
1.0
A
I
IH
Input High Current
V
IN
= V
FB
= 0V
1.0
A
R
DS(ON)H
High Side Switch On Resistance
T
A
= 25C
110
150
m
R
DS(ON)L
Low Side Switch On Resistance
T
A
= 25C
100
150
m
F
OSC
Oscillator Frequency
T
A
= 25C
750
1000
1250
kHz
T
SD
Over-Temperature Shutdown
140
C
Threshold
T
HYS
Over-Temperature Shutdown
15
C
Hysteresis
1. The AAT1157 is guaranteed to meet performance specifications over the -40C to +85C operating temperature range and is assured
by design, characterization, and correlation with statistical process controls.
AAT1157
1MHz 1.2A Buck DC/DC Converter
1157.2005.11.1.4
5
Typical Characteristics
Frequency vs. Input Voltage
(V
OUT
= 1.8V)
Input Voltage (V)
Frequency (MHz)
1.2
1.22
1.24
1.26
1.28
1.3
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Output Voltage vs. Temperature
(V
IN
= 3.6V; V
OUT
= 2.5V; I
OUT
= 1.0A)
Temperature (
C)
Output Voltage Error (%)
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
-40
-20
0
20
40
60
80
100
N-Channel R
DSON
vs. Input Voltage
Input Voltage (V)
R
DSON
(m
)
0
20
40
60
80
100
120
140
160
180
200
2.5
3
3.5
4
4.5
5
5.5
120
C
100
C
25
C
85
C
P-Channel R
DSON
vs. Input Voltage
Input Voltage (V)
R
DSON
(m
)
0
20
40
60
80
100
120
140
160
180
200
2.5
3
4
3.5
4.5
5
5.5
120
C
100
C
25
C
85
C
DC Regulation
(V
OUT
= 2.5V)
Output Current (mA)
Output Error (%)
-4.0
-3.0
-2.0
-1.0
0.0
1.0
2.0
1
10
100
1000
10000
V
IN
= 3.0V
V
IN
= 3.3V
V
IN
= 3.6V
No Load Supply Current vs. Input Voltage
Input Voltage (V)
Supply Current (
A)
0
50
100
150
200
250
300
2.5
3
4
3.5
4.5
5.5
5
-40
C
25
C
85
C
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