AAT1121
1.5MHz, 250mA Step-Down Converter
General Description
The AAT1121 SwitchReg is a 1.5MHz step-down
converter with an input voltage range of 2.7V to
5.5V and output as low as 0.6V. Its low supply
current, small size, and high switching frequency
make the AAT1121 the ideal choice for portable
applications.
The AAT1121 delivers 250mA of load current, while
maintaining a low 30µA no load quiescent current.
The 1.5MHz switching frequency minimizes the size
of external components, while keeping switching
losses low. The AAT1121 feedback and control
delivers excellent load regulation and transient
response with a small output inductor and capacitor.
The AAT1121 is available in a Pb-free, 8-pin,
2x2mm TDFN or STDFN package and is rated
over the -40°C to +85°C temperature range.
Features
•
•
•
•
•
•
•
•
•
•
•
•
•
SwitchReg
™
V
IN
Range: 2.7V to 5.5V
V
OUT
Range: 0.6V to V
IN
250mA Max Output Current
Up to 96% Efficiency
30µA Typical Quiescent Current
1.5MHz Switching Frequency
Soft-Start Control
Over-Temperature and Current Limit
Protection
100% Duty Cycle Low-Dropout Operation
<1µA Shutdown Current
Small External Components
Ultra-Small TDFN22-8 or STDFN22-8
Package
Temperature Range: -40°C to +85°C
Applications
•
•
•
•
•
•
Bluetooth™ Headsets
Cellular Phones
Digital Cameras
Handheld Instruments
Portable Music Players
USB Devices
Typical Application
V
IN
AAT1121
VP
VIN
C
1
4.7µF
EN
FB
LX
L1
3.0μH
R
1
118kΩ
R
2
59kΩ
C
2
4.7µF
V
O
= 1.8V
250mA
GND
PGND
1121.2007.03.1.2
1
AAT1121
1.5MHz, 250mA Step-Down Converter
Pin Descriptions
Pin #
1
2
3
4
5
6
7
8
EP
Symbol
VP
VIN
GND
FB
N/C
EN
LX
PGND
Function
Input power pin; connected to the source of the P-channel MOSFET.
Connect to the input capacitor.
Input bias voltage for the converter.
Non-power signal ground pin.
Feedback input pin. Connect this pin to an external resistive divider for
adjustable output.
No connect.
Enable pin. A logic high enables normal operation. A logic low shuts down
the converter.
Switching node. Connect the inductor to this pin. It is connected internally to
the drain of both high- and low-side MOSFETs.
Input power return pin; connected to the source of the N-channel MOSFET.
Connect to the output and input capacitor return.
Exposed paddle (bottom): connect to ground directly beneath the package.
Pin Configuration
TDFN22-8/STDFN22-8
(Top View)
VP
VIN
GND
FB
1
2
3
4
8
7
6
5
PGND
LX
EN
N/C
2
1121.2007.03.1.2
AAT1121
1.5MHz, 250mA Step-Down Converter
Absolute Maximum Ratings
1
Symbol
V
IN
V
LX
V
OUT
V
EN
T
J
T
LEAD
Description
Input Voltage and Bias Power to GND
LX to GND
FB to GND
EN to GND
Operating Junction Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
Value
6.0
-0.3 to V
IN
+ 0.3
-0.3 to V
IN
+ 0.3
-0.3 to 6.0
-40 to 150
300
Units
V
V
V
V
°C
°C
Thermal Information
Symbol
P
D
θ
JA
Description
Maximum Power Dissipation
Thermal Resistance
2
Value
2
50
Units
W
°C/W
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. Mounted on an FR4 board.
1121.2007.03.1.2
3
AAT1121
1.5MHz, 250mA Step-Down Converter
Electrical Characteristics
1
V
IN
= 3.6V, T
A
= -40°C to +85°C, unless otherwise noted; typical values are T
A
= 25°C.
Symbol
V
IN
V
UVLO
V
OUT
V
OUT
I
Q
I
SHDN
I
LIM
R
DS(ON)H
R
DS(ON)L
I
LXLEAK
ΔV
Linereg
/ΔV
IN
V
FB
I
FB
F
OSC
T
S
T
SD
T
HYS
V
EN(L)
V
EN(H)
I
EN
Description
Input Voltage
UVLO Threshold
Conditions
V
IN
Rising
Hysteresis
V
IN
Falling
I
OUT
= 0 to 250mA,
V
IN
= 2.7V to 5.5V
No Load
EN = GND
Min
2.7
Typ
Max
5.5
2.6
Units
V
V
mV
V
%
V
µA
µA
mA
Ω
Ω
µA
%/V
V
µA
MHz
µs
°C
°C
V
V
µA
250
2.0
-3.0
0.6
30
1.0
600
0.59
0.42
3.0
V
IN
Output Voltage Tolerance
2
Output Voltage Range
Quiescent Current
Shutdown Current
P-Channel Current Limit
High-Side Switch On Resistance
Low-Side Switch On Resistance
LX Leakage Current
Line Regulation
Feedback Threshold Voltage Accuracy
FB Leakage Current
Oscillator Frequency
Startup Time
Over-Temperature Shutdown Threshold
Over-Temperature Shutdown Hysteresis
Enable Threshold Low
Enable Threshold High
Input Low Current
V
IN
= 5.5V, V
LX
= 0 to V
IN
V
IN
= 2.7V to 5.5V
V
IN
= 3.6V
V
OUT
= 1.0V
From Enable to Output
Regulation
1.0
0.591
0.2
0.600
1.5
100
140
15
0.6
1.4
-1.0
0.609
0.2
V
IN
= V
EN
= 5.5V
1.0
1. The AAT1121 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured
by design, characterization, and correlation with statistical process controls.
2. Output voltage tolerance is independent of feedback resistor network accuracy.
4
1121.2006.10.1.2
1121.2007.03.1.2
AAT1121
1.5MHz, 250mA Step-Down Converter
Typical Characteristics
Efficiency vs. Load
(V
OUT
= 1.2V; L = 1.5µH)
100
90
1.0
DC Load Regulation
(V
OUT
= 1.2V; L = 1.5µH)
V
IN
= 2.7V
Output Error (%)
Efficiency (%)
80
70
60
50
40
30
0.1
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 5.0V
0.5
V
IN
= 3.6V
0.0
-0.5
V
IN
= 2.7V
V
IN
= 4.2V
1
10
100
1000
-1.0
0.1
1
10
100
1000
Output Current (mA)
Output Current (mA)
Efficiency vs. Load
(V
OUT
= 1.8V; L = 3.3µH)
100
90
1.0
DC Load Regulation
(V
OUT
= 1.8V; L = 3.3µH)
V
IN
= 2.7V
Output Error (%)
Efficiency (%)
V
IN
= 3.6V
0.5
80
70
60
50
40
0.1
1
10
100
1000
V
IN
= 3.6V
0.0
V
IN
= 4.2V
V
IN
= 2.7V
-0.5
V
IN
= 4.2V
1
10
100
1000
-1.0
0.1
Output Current (mA)
Output Current (mA)
Efficiency vs. Load
(V
OUT
= 3.0V; L = 4.7µH)
100
90
1.0
DC Load Regulation
(V
OUT
= 3.0V; L = 4.7µH)
V
IN
= 3.6V
Output Error (%)
0.5
Efficiency (%)
80
70
60
50
40
V
IN
= 4.2V
V
IN
= 5.0V
V
IN
= 4.2V
0.0
V
IN
= 3.6V
V
IN
= 5.0V
-0.5
-1.0
0.1
1
10
100
1000
0.1
1
10
100
1000
Output Current (mA)
Output Current (mA)
1121.2007.03.1.2
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