AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
1149A.2008.08.1.1 1
www.analogictech.com
General Description
The AAT1149A SwitchReg is a 2.2MHz step-down con-
verter with an input voltage range of 2.2V to 5.5V. It is
optimized to react quickly to load variations and operate
with a tiny 0603 inductor that is only 1mm tall.
The AAT1149A can deliver 400mA of load current and
operates in PWM only mode for low noise operation. The
2.2MHz switching frequency minimizes the size of exter-
nal components while keeping switching losses low.
The AAT1149A is optimized for low noise portable
applications.
The AAT1149A is available in a Pb-free, space-saving
5-pin wafer-level chip scale (WLCSP) package and is
rated over the -40°C to +85°C temperature range.
Features
• Ultra-Small 0603 Inductor (Height = 1mm)
• VIN Range: 2.2V to 5.5V
• VOUT Fixed 1.875V
• 400mA Max Output Current
• Up to 98% Efficiency
• 3mA No Load Quiescent Current
• 2.2MHz Switching Frequency
• 70μs Soft Start
• Fast Load Transient
• Over-Temperature Protection
• Current Limit Protection
• 100% Duty Cycle Low-Dropout Operation
• <1μA Shutdown Current
• 0.9x1.2mm WLCSP Package
• Temperature Range: -40°C to +85°C
Applications
• Cellular Phones
• Digital Cameras
• Handheld Instruments
• Microprocessor / DSP Core / IO Power
• PDAs and Handheld Computers
• USB Devices
Typical Application
L1 2.2µH
C1
4.7µF
VOUT = 1.875VVIN = 3.6V
C2
4.7µF
EN FB
IN LX
AGND
PGND
PGND
PGND
AAT1149A
U1
AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
2 1149A.2008.08.1.1
www.analogictech.com
AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
2 1149A.2008.08.1.1
www.analogictech.com
Pin Descriptions
Pin # Symbol Function
1 FB Feedback input pin. Connect this pin ito the converted output voltage node.
2 EN Enable pin.
3AGND Non-power signal ground pin.
PGND Main power ground return pins. Connect to the output and input capacitor return.
4 IN Input supply voltage for the converter.
5LX
Switching node. Connect the inductor to this pin. It is internally connected to the drain of both high- and
low-side MOSFETs.
Pin Configuration
WLCSP-5
(Top View)
A
GND/PGND
IN
FB
LX
EN
12
4
3
5
AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
1149A.2008.08.1.1 3
www.analogictech.com
AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
1149A.2008.08.1.1 3
www.analogictech.com
Absolute Maximum Ratings1
Symbol Description Value Units
VIN Input Voltage to GND 6.0 V
VLX LX to GND -0.3 to VIN + 0.3 V
VFB FB to GND -0.3 to VIN + 0.3 V
VEN EN to GND -0.3 to 6.0 V
TJOperating Junction Temperature Range -40 to 150 °C
TLEAD Maximum Soldering Temperature (at leads, 10 sec) 300 °C
Thermal Information
Symbol Description Value Units
PDMaximum Power Dissipation2, 3 352 mW
θJA Thermal Resistance2 284 °C/W
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent 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. Mounted on an FR4 board; use the NSMD (none-solder mask defined) pad style for tighter control on the copper etch process.
3. Derate 3.52 mW/°C above 25°C.
AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
4 1149A.2008.08.1.1
www.analogictech.com
AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
4 1149A.2008.08.1.1
www.analogictech.com
Electrical Characteristics1
VIN = 3.6V, TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C.
Symbol Description Conditions Min Typ Max Units
Step-Down Converter
VIN Input Voltage 2.2 5.5 V
VOUT Output Voltage Tolerance IOUT = 0 to 400mA, VIN = 2.7V to 5.5V -3.0 3.0 %
IQQuiescent Current No Load 3 6 mA
ISHDN Shutdown Current VEN = GND 1.0 μA
ILIM P-Channel Current Limit 600 mA
RDS(ON)H High Side Switch On Resistance 0.40 Ω
RDS(ON)L Low Side Switch On Resistance 0.35 Ω
ILXLEAK LX Leakage Current VIN = 5.5V, VLX = 0 to VIN, VEN = GND 1 μA
ΔVLinereg Line Regulation VIN = 2.7V to 5.5V 0.1 %/V
TSStart-Up Time From Enable to Output Regulation 70 μs
FOSC Oscillator Frequency TA = 25°C 2.2 MHz
TSD Over-Temperature Shutdown Threshold 140 °C
THYS Over-Temperature Shutdown Hysteresis 15 °C
EN
VEN(L) Enable Threshold Low 0.6 V
VEN(H) Enable Threshold High 1.4 V
IEN Input Low Current VIN = VOUT = 5.5V -1.0 1.0 μA
1. The AAT1149A is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and cor-
relation with statistical process controls.
AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
1149A.2008.08.1.1 5
www.analogictech.com
AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
1149A.2008.08.1.1 5
www.analogictech.com
Typical Characteristics
Efficiency vs. Output Current
(VOUT = 1.875V)
Output Current (A)
Efficiency (%)
0
10
20
30
40
50
60
70
80
90
100
10001001010.1
VIN = 5V
VIN = 4.2V
VIN = 3.6V
VIN = 3V
VIN = 2.7V
Load Regulation
(VOUT = 1.875V)
Output Current (A)
Output Error (%)
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
100 1000
10
1
0.1
VIN = 5V
VIN = 4.2V
VIN = 3.6V
VIN = 3V
VIN = 2.2V
No Load Quiescent Current vs. Input Voltage
Input Voltage (V)
Supply Current (µA)
65432.5 3.5 4.5 5.5
1
1.5
2
2.5
3
3.5
4
4.5
5
T = 85°C
T = 25°C
T = -40°C
Frequency Variation vs. Input Voltage
(VOUT = 1.875V)
Input Voltage (V)
Frequency Variation (%)
-4
-3
-2
-1
0
1
2
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
Switching Frequency Variation vs. Temperature
Temperature (°
°
C)
Variation (%)
-10
-8
-6
-4
-2
0
2
4
6
8
10
-40 -20 0 20 40 60 80 100 120
Output Voltage Error vs. Temperature
(VIN = 3.6V; VO = 1.875V; IOUT = 400mA)
Temperature (°
°
C)
Output Error (%)
-2.0
-1.0
0.0
1.0
2.0
-40 -20 0 20 40 60 80 100
AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
6 1149A.2008.08.1.1
www.analogictech.com
AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
6 1149A.2008.08.1.1
www.analogictech.com
Typical Characteristics
Line Regulation
(VOUT = 1.875V)
Input Voltage (V)
Accuracy (%)
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
2.5 3 3.5 4 4.5 5 5.5 6
400mA
600mA
0mA
100mA
Line Transient
(VOUT = 1.875V; VIN = 3.6V to 4.2V)
Time (200µs/div)
Input Voltage (top) (1V/div)
Output Voltage
(bottom) (20mV/div)
0
1
2
3
4
5
-0.02
0
0.02
0.04
Line Transient
(VOUT = 1.875V; No Load)
Time (50µs/div)
Input Voltage (top) (V)
Output Voltage (bottom) (V)
2.50
2.75
3.00
3.25
3.50
3.75
4.00
4.25
4.50
1.78
1.80
1.82
1.84
1.86
1.88
1.90
1.92
1.94
N-Channel RDS(ON) vs. Input Voltage
(WLCSP-5)
Input Voltage (V)
RDS(ON) (mΩ
Ω
)
250
300
350
400
450
500
550
600
650
700
750
2.5 3 3.5 4 4.5 5 5.5 6
120°C100°C
85°C
25°C
P-Channel RDS(ON) vs. Input Voltage
(WLCSP-5)
Input Voltage (V)
RDS(ON) (mΩ
Ω
)
250
300
350
400
450
500
550
600
650
700
750
2.5 3 3.5 4 4.5 5 5.5 6
25°C
85°C
120°C100°C
Load Transient
(VOUT = 1.875V; VIN = 3.6V; IOUT = 1mA to 400mA)
Time (100µs/div)
Output Current (middle)
Inductor Current (bottom)
(500mA/div)
Output Voltage (top)
(200mV/div)
-0.2
0
0.2
0
0.5
0
0.5
AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
1149A.2008.08.1.1 7
www.analogictech.com
Typical Characteristics
Load Transient
(VOUT = 1.875V; VIN = 3.6V; IOUT = 10mA to 400mA)
Time (100µs/div)
Output Current (middle)
Inductor Current (bottom)
(500mA/div)
Output Voltage (top)
(200mV/div)
-0.2
0
0.2
0
0.5
0
0.5
Soft Start
(VOUT = 1.875V)
Time (50µs/div)
Inductor Current
(bottom) (250mA/div)
Enable and Output Voltage
(top) (V)
-4.00
-3.00
-2.00
-1.00
0.00
1.00
2.00
3.00
4.00
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
8 1149A.2008.08.1.1
www.analogictech.com
AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
8 1149A.2008.08.1.1
www.analogictech.com
Functional Description
The AAT1149A is a high performance 400mA 2.2MHz
monolithic step-down converter. It minimizes external
component size, enabling the use of a tiny 0603 inductor
that is only 1mm tall, and is optimized for low noise.
Apart from the small bypass input capacitor, only a small
L-C filter is required at the output. Typically, a 1.8μH
inductor and a 4.7μF ceramic capacitor are recommend-
ed (see table of values).
Only three external power components (CIN, COUT
, and L)
are required. Output voltage is fixed internally.
At dropout, the converter duty cycle increases to 100%
and the output voltage tracks the input voltage minus
the RDS(ON) drop of the P-channel high-side MOSFET.
The input voltage range is 2.2V to 5.5V. The converter
efficiency has been optimized for all load conditions,
ranging from no load to 400mA.
The internal error amplifier and compensation provides
excellent transient response, load, and line regulation.
Soft start eliminates any output voltage overshoot when
the enable or the input voltage is applied.
Functional Block Diagram
EN
LX
Err
.
Amp
Logic
DH
DL
PGND
IN
Voltage
Reference
INPUT
FB
AGND
AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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Control Loop
The AAT1149A is a peak current mode step-down con-
verter. The current through the P-channel MOSFET (high
side) is sensed for current loop control, as well as short
circuit and overload protection. A fixed slope compensa-
tion signal is added to the sensed current to maintain
stability for duty cycles greater than 50%. The peak cur-
rent mode loop appears as a voltage-programmed cur-
rent source in parallel with the output capacitor.
The output of the voltage error amplifier programs the
current mode loop for the necessary peak switch current
to force a constant output voltage for all load and line
conditions. Internal loop compensation terminates the
transconductance voltage error amplifier output. For the
adjustable output, the error amplifier reference is fixed
at 0.6V.
Soft Start / Enable
Soft start limits the current surge seen at the input and
eliminates output voltage overshoot. When pulled low,
the enable input forces the AAT1149A into a low-power,
non-switching state. The total input current during shut-
down is less than 1μA.
Current Limit and
Over-Temperature Protection
For overload conditions, the peak input current is limit-
ed. To minimize power dissipation and stresses under
current limit and short-circuit conditions, switching is
terminated after entering current limit for a series of
pulses. Switching is terminated for seven consecutive
clock cycles after a current limit has been sensed for a
series of four consecutive clock cycles.
Thermal protection completely disables switching when
internal dissipation becomes excessive. The junction
over-temperature threshold is 140°C with 15°C of hys-
teresis. Once an over-temperature or over-current fault
conditions is removed, the output voltage automatically
recovers.
Applications Information
Inductor Selection
The step-down converter uses peak current mode con-
trol with slope compensation to maintain stability for
duty cycles greater than 50%. The output inductor value
must be selected so the inductor current down slope
meets the internal slope compensation requirements. A
2.2μH inductor is recommended for a 1.875V output.
Manufacturer’s specifications list both the inductor DC
current rating, which is a thermal limitation, and the
peak current rating, which is determined by the satura-
tion characteristics. The inductor should not show any
appreciable saturation under normal load conditions.
Some inductors may meet the peak and average current
ratings yet result in excessive losses due to a high DCR.
Always consider the losses associated with the DCR and
its effect on the total converter efficiency when selecting
an inductor.
The 2.2μH CBC2518 series inductor selected from Taiyo
Yuden has a 130mW DCR and a 890mA saturation cur-
rent rating. At full load, the inductor DC loss is 21mW
which gives a 2.8% loss in efficiency for a 400mA,
1.875V output.
Input Capacitor
Select a 4.7μF to 10μF X7R or X5R ceramic capacitor for
the input. To estimate the required input capacitor size,
determine the acceptable input ripple level (VPP) and solve
for C. The calculated value varies with input voltage and
is a maximum when VIN is double the output voltage.
⎛⎞
· 1 -
⎝⎠
VO
VIN
CIN =
VO
VIN
⎛⎞
- ESR · FS
⎝⎠
VPP
IO
⎛⎞
· 1 - = for VIN = 2 · V
O
⎝⎠
VO
VIN
VO
VIN
1
4
CIN(MIN) = 1
⎛⎞
- ESR · 4 · FS
⎝⎠
VPP
IO
Always examine the ceramic capacitor DC voltage coef-
ficient characteristics when selecting the proper value.
For example, the capacitance of a 10μF, 6.3V, X5R ceram-
ic capacitor with 5.0V DC applied is actually about 6μF.
AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
10 1149A.2008.08.1.1
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The maximum input capacitor RMS current is:
⎛⎞
IRMS = IO · · 1 -
⎝⎠
VO
VIN
VO
VIN
The input capacitor RMS ripple current varies with the
input and output voltage and will always be less than or
equal to half of the total DC load current.
⎛⎞
· 1 - = D · (1 - D) = 0.52 =
⎝⎠
VO
VIN
VO
VIN
1
2
for VIN = 2 · VO
IO
RMS(MAX)
I2
=
The term ⎛⎞
· 1 -
⎝⎠
VO
VIN
VO
VIN appears in both the input voltage rip-
ple and input capacitor RMS current equations and is a
maximum when VO is twice VIN. This is why the input
voltage ripple and the input capacitor RMS current ripple
are a maximum at 50% duty cycle.
The input capacitor provides a low impedance loop for the
edges of pulsed current drawn by the AAT1149A. Low
ESR/ESL X7R and X5R ceramic capacitors are ideal for
this function. To minimize stray inductance, the capacitor
should be placed as closely as possible to the IC. This
keeps the high frequency content of the input current
localized, minimizing EMI and input voltage ripple.
The proper placement of the input capacitor (C2) can be
seen in the evaluation board layout in Figure 1.
A laboratory test set-up typically consists of two long
wires running from the bench power supply to the evalu-
ation board input voltage pins. The inductance of these
wires, along with the low-ESR ceramic input capacitor,
can create a high Q network that may affect converter
performance. This problem often becomes apparent in
the form of excessive ringing in the output voltage dur-
ing load transients. Errors in the loop phase and gain
measurements can also result.
Since the inductance of a short PCB trace feeding the
input voltage is significantly lower than the power leads
from the bench power supply, most applications do not
exhibit this problem.
In applications where the input power source lead induc-
tance cannot be reduced to a level that does not affect
the converter performance, a high ESR tantalum or alu-
minum electrolytic should be placed in parallel with the
low ESR, ESL bypass ceramic. This dampens the high Q
network and stabilizes the system.
Output Capacitor
The output capacitor limits the output ripple and pro-
vides holdup during large load transitions. A 4.7μF to
10μF X5R or X7R ceramic capacitor typically provides
sufficient bulk capacitance to stabilize the output during
large load transitions and has the ESR and ESL charac-
teristics necessary for low output ripple.
The output voltage droop due to a load transient is dom-
inated by the capacitance of the ceramic output capaci-
tor. During a step increase in load current, the ceramic
output capacitor alone supplies the load current until the
loop responds. Within two or three switching cycles, the
loop responds and the inductor current increases to
match the load current demand. The relationship of the
output voltage droop during the three switching cycles to
the output capacitance can be estimated by:
COUT =
3 · ΔILOAD
VDROOP · FS
Once the average inductor current increases to the DC
load level, the output voltage recovers. The above equa-
tion establishes a limit on the minimum value for the
output capacitor with respect to load transients.
The internal voltage loop compensation also limits the
minimum output capacitor value to 4.7μF. This is due to
its effect on the loop crossover frequency (bandwidth),
phase margin, and gain margin. Increased output capac-
itance will reduce the crossover frequency with greater
phase margin.
The maximum output capacitor RMS ripple current is
given by:
1
23
VOUT · (VIN(MAX) - VOUT)
RMS(MAX)
IL · FS · VIN(MAX)
=·
·
Dissipation due to the RMS current in the ceramic output
capacitor ESR is typically minimal, resulting in less than
a few degrees rise in hot-spot temperature.
AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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Figure 1: AAT1149AIUV Evaluation Board Figure 2: AAT1149AIUV Evaluation Board
Top Side. Bottom Side.
VIN
VOUT
C1
4.7μF
C3
open
L1
U1
WLCSP-5
IN
4
22
1
3
1
5
3
LX
FB
GND
EN
EN AAT1149AIUV
C2
4.7μF
R2
open
R1
0
Figure 3: AAT1149AIUV Evaluation Board Schematic.
Thermal Calculations
There are three types of losses associated with the
AAT1149A step-down converter: switching losses, con-
duction losses, and quiescent current losses. Conduction
losses are associated with the RDS(ON) characteristics of the
power output switching devices. Switching losses are
dominated by the gate charge of the power output switch-
ing devices. At full load, assuming continuous conduction
mode (CCM), a simplified form of the losses is given by:
PTOTAL
IO
2 · (RDS(ON)H · VO + RDS(ON)L · [VIN - VO])
VIN
=
+ (tsw · FS · IO + IQ) · VIN
IQ is the step-down converter quiescent current. The
term tsw is used to estimate the full load step-down con-
verter switching losses.
AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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For the condition where the step-down converter is in
dropout at 100% duty cycle, the total device dissipation
reduces to:
PTOTAL = IO
2 · RDS(ON)H + IQ · VIN
Since RDS(ON), quiescent current, and switching losses all
vary with input voltage, the total losses should be inves-
tigated over the complete input voltage range.
Given the total losses, the maximum junction tempera-
ture can be derived from the θJA for the WLCSP-8 pack-
age which is 284°C/W.
TJ(MAX) = PTOTAL · ΘJA + TAMB
WLCSP Package Light Sensitivity
The electrical performance of the WLCSP package can be
adversely affected by exposing the device to certain light
sources such as direct sunlight or a halogen lamp whose
wavelengths are red and infra-reds. However, fluores-
cent lighting has very little effect on the electrical perfor-
mance of the WLCSP package.
Layout
The suggested PCB layout for the AAT1149A is shown in
Figures 1 and 2. The following guidelines should be used
to help ensure a proper layout.
1. The input capacitor (C2) should connect as closely as
possible to IN (Pin 4) and PGND (Pin 3).
2. C1 and L1 should be connected as closely as possi-
ble. The connection of L1 to the LX pin should be as
short as possible.
3. The feedback trace or FB pin (Pin 1) should be sepa-
rate from any power trace and connect as closely as
possible to the load point. Sensing along a high-
current load trace will degrade DC load regulation.
4. The resistance of the trace from the load return to
the PGND (Pin 3) should be kept to a minimum. This
will help to minimize any error in DC regulation due
to differences in the potential of the internal signal
ground and the power ground.
5. The pad on the PCB for the WLCSP-5 package should
use NSMD (non-solder mask defined) configuration
due to its tighter control on the copper etch process.
A pad thickness of less than 1oz is recommended to
achieve higher stand-off.
AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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Step-Down Converter Design Example
Specifications
VO = 1.875V @ 400mA (adjustable using 0.6V version), Pulsed Load DILOAD = 300mA
VIN = 2.7V to 4.2V (3.6V nominal)
FS = 2.2MHz
TAMB = 85°C
1.875V Output Inductor
L1 = 1 · V
O
= 1 · 1.875V = 1.875µH
µs
A
µs
A
(use 2.2μH)
For Taiyo Yuden inductor CBC2518T2R2M, 2.2μH, DCR = 130mΩ.
V
O
V
O
1.875
V
1.875V
ΔI
L1
=
· 1 - = · 1 - = 214m
A
L1 · F
S
V
IN
2.2µH · 2.2MHz
4.2V
I
PKL1
= I
O
+ ΔI
L1
= 0.4A + 0.107A = 0.507A
2
P
L1
= I
O
2
· DCR = 0.4A
2
· 130mΩ = 21mW
1.875V Output Capacitor
VDROOP = 0.1V
1
23
1 1.875V · (4.2V - 1.875V)
2.2µH · 2.2MHz · 4.2V
23
RMS
IL1 · FS · VIN(MAX)
= ·
·
3 · ΔILOAD
VDROOP · FS
3 · 0.3A
0.1V · 2.2MHz
COUT = = = 4.1µF; use 4.7µF
· = 62mArms
·
(VO) · (VIN(MAX) - VO)=
Pesr = esr · IRMS2 = 5mΩ · (62mA)2 = 19µW
AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
14 1149A.2008.08.1.1
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AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
14 1149A.2008.08.1.1
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Input Capacitor
Input Ripple VPP = 10mV
CIN = = = 5.7µF; use 4.7µF
1
- ESR · 4 · FS
VPP
IO
1
- 5mΩ · 4 · 2.2MHz
10mV
0.4A
IO
RMS
I
P
= esr · IRMS
2 = 5mΩ · (0.2A)2 = 0.2mW
2
= = 0.2Arms
AAT1149A Losses (WLCSP-5 Package)
PTOTAL
+ (tsw · FS · IO + IQ) · VIN
IO
2 · (RDS(ON)H · VO + RDS(ON)L · [VIN -VO])
VIN
=
=
+ (5ns · 2.2MHz · 0.4A + 3mA) · 4.2V = 149mW
0.42 · (0.725Ω · 1.875V + 0.7Ω · [4.2V - 1.875V])
4.2V
TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (284°C/W) · 149mW = 127°C
AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
1149A.2008.08.1.1 15
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AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
1149A.2008.08.1.1 15
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Manufacturer Part Number/Type Inductance (μH)
Rated
Current (mA) DCR (Ω)
Size (mm)
LxWxH
Taiyo Yuden
BRL2012 2.2 550 250 0805
(HMAX = 1mm)
CBC2518
Wire Wound Chip 2.2 890 130 2.5x1.8x1.8
Sumida CDRH2D09
Shielded 2.5 440 150 3.2x3.2x1.0
Murata LQH2MCN4R7M02
Unshielded 2.2 425 480 2.0x1.6x0.95
Coiltronics SD3118
Shielded 2.2 510 116 3.15x3.15x1.2
Table 1: Typical Surface Mount Inductors.
Manufacturer Part Number Value Voltage Temp. Co. Case
Murata GRM219R61A475KE19 4.7μF 10V X5R 0805
Murata GRM21BR60J106KE19 10μF 6.3V X5R 0805
Murata GRM185R60J475M 4.7μF 6.3V X58 0603
Table 2: Surface Mount Capacitors.
1. For reduced quiescent current, R2 = 221kΩ.
AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
16 1149A.2008.08.1.1
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AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
16 1149A.2008.08.1.1
www.analogictech.com
Ordering Information
Output Voltage1Package Marking Part Number (Tape and Reel)2
1.875 WLCSP-5 3UYW3AAT1149AIUV-1.875-T1
All AnalogicTech products are offered in Pb-free packaging. The term “Pb-free” means semiconductor
products that are in compliance with current RoHS standards, including the requirement that lead not exceed
0.1% by weight in homogeneous materials. For more information, please visit our website at
http://www.analogictech.com/about/quality.aspx.
Package Information
WLCSP-5
0.910
±
0.035
0.400 BSC
60°
0.400 BSC
1.235
±
0.035
0.693 BSC
Bottom View Top View
0.200
±
0.030
0.300
0.300
0.070
0.140
Line_1
Line_1: Part Code
Line_2: Year Code + Date Code
Line_2
ø 0.2 (Ref.)
Pin 1 indication
0.580
+
0.030
-0.070
End View
Side View
0.380
0.180 + 0.030
- 0.025
All dimensions in millimeters.
1. Contact Sales for other voltage options.
3. Sample stock is generally held on part numbers listed in BOLD.
3. YW = date code (year, week) for WLCSP-5 package.
AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
1149A.2008.08.1.1 17
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AAT1149A
2.2MHz Fast Transient 400mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
1149A.2008.08.1.1 17
www.analogictech.com
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