1
AAT1149
3MHz Fast Transient 400mA Step-Down Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201987B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
General Description
The AAT1149 SwitchReg is a 3.0MHz step-down con-
verter with an input voltage range of 2.7V to 5.5V and
output voltage as low as 1.0V. It is optimized to react
quickly to load variations and operate with a tiny 0603
inductor that is only 1mm tall.
The AAT1149 output voltage is programmable via exter-
nal feedback resistors. It can deliver 400mA of load cur-
rent while maintaining a low 45μA no load quiescent
current. The 3.0MHz switching frequency minimizes the
size of external components while keeping switching
losses low.
The AAT1149 maintains high efficiency throughout
the operating range, which is critical for portable
applications.
The AAT1149 is available in a Pb-free, space-saving
2.0x2.2mm SC70JW-8 package or a 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: 2.7V to 5.5V
• VOUT Adjustable from 1.0V to VIN
• 400mA Max Output Current
• Up to 98% Efficiency
• 45μA No Load Quiescent Current
• 3.0MHz Switching Frequency
• 70μs Soft Start
• Fast Load Transient
• Over-Temperature Protection
• Current Limit Protection
• 100% Duty Cycle Low-Dropout Operation
• <1μA Shutdown Current
• SC70JW-8 or 0.91x1.235mm 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 1.8µH
C1
4.7µF
R1
118k
R2
59k
VOUT = 1.8VVIN = 3.6V
C2
4.7µF
EN FB
IN LX
AGND
PGND
PGND
PGND
AAT1149
U1
2
AAT1149
3MHz Fast Transient 400mA Step-Down Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201987B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
Pin Descriptions
Pin #
SC70JW-8 WLCSP Symbol Function
1 2 EN Enable pin.
21FB
Feedback input pin. This pin is connected to an external resistive divider for an adjustable
output.
3 4 IN Input supply voltage for the converter.
45LX
Switching node. Connect the inductor to this pin. It is internally connected to the drain of both
high- and low-side MOSFETs.
53AGND Non-power signal ground pin.
6, 7, 8 PGND Main power ground return pins. Connect to the output and input capacitor return.
Pin Configuration
SC70JW-8 WLCSP-5
(Top View) (Top View)
FB
IN
LX
PGND
PGND
PGND
AGND
EN 1
2
3
45
6
7
8
A
GND/PGND
IN
FB
LX
EN
12
4
3
5
3
AAT1149
3MHz Fast Transient 400mA Step-Down Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201987B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
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 Dissipation SC70JW-82, 3 625 mW
WLCSP-52, 4 352
JA Thermal Resistance2 SC70JW-8 160 °C/W
WLCSP-5 284
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; for the WLCSP package, use the NSMD (none-solder mask defined) pad style for tighter control on the copper etch process.
3. Derate 6.25mW/°C above 25°C.
4. Derate 3.52 mW/°C above 25°C.
4
AAT1149
3MHz Fast Transient 400mA Step-Down Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201987B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
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 2.7 5.5 V
VIN Rising 2.7 V
VUVLO UVLO Threshold Hysteresis 100 mV
VIN Falling 1.8 V
VOUT Output Voltage Tolerance IOUT = 0 to 400mA, VIN = 2.7V to 5.5V -3.0 3.0 %
VOUT Adjustable Output Voltage Range 1.0 VIN V
IQQuiescent Current No Load 45 70 μA
ISHDN Shutdown Current VEN = GND 1.0 μA
ILIM P-Channel Current Limit 600 mA
RDS(ON)H High Side Switch On Resistance SC70JW-8 0.45
WLCSP-5 0.40
RDS(ON)L Low Side Switch On Resistance SC70JW-8 0.40
WLCSP-5 0.35
ILXLEAK LX Leakage Current VIN = 5.5V, VLX = 0 to VIN, VEN = GND 1 μA
VLinereg Line Regulation VIN = 2.7V to 5.5V 0.1 %/V
VOUT Out Threshold Voltage Accuracy 0.6V Output, No Load, TA = 25°C 591 600 609 mV
IOUT Out Leakage Current 0.6V Output 0.2 μA
TSStart-Up Time From Enable to Output Regulation 70 μs
FOSC Oscillator Frequency TA = 25°C 3.0 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 AAT1149 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and correla-
tion with statistical process controls.
5
AAT1149
3MHz Fast Transient 400mA Step-Down Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201987B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
Typical Characteristics
Efficiency vs. Load Current
(VOUT = 3V; L = 3µH)
Load Current (mA)
Efficiency (%)
50
60
70
80
90
100
0.1 1 10 100 1000
VIN = 3.3V
VIN = 4.2V VIN = 5V
Load Regulation
(VOUT = 3V; L = 3µH)
Load Current (mA)
Output Error (%)
-1.00
-0.75
-0.50
-0.25
0.00
0.25
0.50
0.75
1.00
0.1 1 10 100 1000
VIN = 4.2V
VIN = 5V
VIN = 3.3V
Efficiency vs. Load Current
(VOUT = 1.8V; L = 2.2µH)
Load Current (mA)
Efficiency (%)
50
60
70
80
90
100
0.1 1 10 100 100
0
VIN = 4.2V
VIN = 2.7V
VIN = 3.6V
VIN = 5V
VIN = 3V
Load Regulation
(VOUT = 1.8V; L = 2.2µH)
Load Current (mA)
Output Error (%)
-1.00
-0.75
-0.50
-0.25
0.00
0.25
0.50
0.75
1.00
0.1 1 10 100 100
0
VIN = 2.7V
VIN = 4.2V
VIN = 3V
VIN = 3.6VVIN = 5V
No Load Quiescent Current vs. Input Voltage
Input Voltage (V)
Supply Current (µA)
0
10
20
30
40
50
60
70
2.5 3 3.5 4 4.5 5 5.5 6
85°C
-40°C
25°C
Switching Frequency vs. Input Voltage
Input Voltage (V)
Frequency Variation (%)
-4
-3
-2
-1
0
1
2
2.5 3 3.5 4 4.5 5 5.
5
VOUT = 1.1V
VOUT = 1.8V VOUT = 3V
6
AAT1149
3MHz Fast Transient 400mA Step-Down Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201987B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
Typical Characteristics
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 = 1.8V; IOUT = 400mA)
Temperature (°
°
C)
Output Error (%)
-2.0
-1.0
0.0
1.0
2.0
-40 -20 0 20 40 60 80 100
Line Regulation
(VOUT = 3V)
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
0mA
400mA
100mA
1mA
600mA
300mA
Line Regulation
(VOUT = 1.8V)
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 Regulation
(VOUT = 1.1V)
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
1mA 0mA
600mA 400mA
Line Transient
(VOUT = 1.8; 400mA Load; No Feedforward Capacitor)
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
1.74
1.76
1.78
1.80
1.82
1.84
1.86
1.88
1.90
7
AAT1149
3MHz Fast Transient 400mA Step-Down Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201987B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
Typical Characteristics
Line Transient
(VOUT = 1.8; No Load; No Feedforward Capacitor)
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
Line Transient
(VOUT = 1.8; CFF = 100pF)
Time (20µs/div)
Input Voltage (top) (V)
Output Voltage (bottom) (V)
1.78
1.79
1.80
1.81
1.82
1.83
1.84
1.85
1.86
2.50
2.75
3.00
3.25
3.50
3.75
4.00
4.25
4.50
N-Channel RDS(ON) vs. Input Voltage
(SC70JW-8)
Input Voltage (V)
RDS(ON) (mΩ
Ω
)
300
350
400
450
500
550
600
650
700
750
2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
25°C
120°C100°C
85°C
P-Channel RDS(ON) vs. Input Voltage
(SC70JW-8)
Input Voltage (V)
RDS(ON) (mΩ
Ω
)
300
350
400
450
500
550
600
650
700
750
2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
25°C
120°C 100°C
85°C
N-Channel RDS(ON) vs. Input Voltage
(WLCSP-5)
Input Voltage (V)
RDS(ON) (mΩ
)
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
8
AAT1149
3MHz Fast Transient 400mA Step-Down Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201987B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
Typical Characteristics
Load Transient
(VOUT = 1.1V; No Feedforward Capacitor)
Time (50µs/div)
Load and Inductor Current
(bottom) (A)
Output Voltage (top) (V)
0.50
0.60
0.70
0.80
0.90
1.00
1.10
1.20
1.30
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
1mA
400mA
Load Transient
(VOUT = 1.1V; CFF = 100pF)
Time (50µs/div)
Load and Inductor Current
(bottom) (A)
Output Voltage (top) (V)
0.50
0.60
0.70
0.80
0.90
1.00
1.10
1.20
1.30
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
1mA
400mA
Load Transient
(VOUT = 1.8V; No Feedforward Capacitor)
Time (50µs/div)
Load and Inductor Current
(bottom) (A)
Output Voltage (top) (V)
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2.25
0.00
0.25
0.75
1.00
1.25
1.50
1.75
2.00
10mA
400mA
Load Transient
(VOUT = 1.8V; CFF = 100pF)
Time (50µs/div)
Load and Inductor Current
(bottom) (A)
Output Voltage (top) (V)
1.20
1.30
1.40
1.50
1.60
1.70
1.80
1.90
2.00
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
10mA
400mA
Load Transient
(VOUT = 1.8V; No Feedforward Capacitor)
Time (50µs/div)
Load and Inductor Current
(bottom) (A)
Output Voltage (top) (V)
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2.25
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
400mA
1mA
Load Transient
(VOUT = 1.8V; CFF = 100pF)
Time (50µs/div)
Load and Inductor Current
(bottom) (A)
Output Voltage (top) (V)
1.20
1.30
1.40
1.50
1.60
1.70
1.80
1.90
2.00
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
400mA
1mA
9
AAT1149
3MHz Fast Transient 400mA Step-Down Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201987B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
Typical Characteristics
Soft Start
(VOUT = 1.8V; No Feedforward Capacitor)
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
Soft Start
(VOUT = 1.8V; CFF = 100pF)
Time (50µs/div)
Inductor Current
(bottom) (250mA/div)
Enable and Output Voltage
(top) (V)
-1.50
-1.00
-0.50
0.00
0.50
1.00
1.50
2.00
2.50
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
Soft Start
(VOUT = 3V; No Feedforward Capacitor)
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
Soft Start
(VOUT = 1.1V; No Feedforward Capacitor)
Time (20µs/div)
Inductor Current
(bottom) (250mA/div)
Enable and Output Voltage
(top) (V)
-0.50
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
-0.75
-0.50
-0.25
0.00
0.25
0.50
0.75
1.00
1.25
10
AAT1149
3MHz Fast Transient 400mA Step-Down Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201987B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
Functional Description
The AAT1149 is a high performance 400mA 3.0MHz
monolithic step-down converter. It minimizes external
component size, enabling the use of a tiny 0603 inductor
that is only 1mm tall, and optimizes efficiency over the
complete load range. 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 recommended (see table of values).
Only three external power components (CIN, COUT
, and L)
are required. Output voltage is programmed with exter-
nal feedback resistors, ranging from 1.0V to the input
voltage. An additional feed-forward capacitor can also be
added to the external feedback to provide improved
transient response (see Figure 4).
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 2.7V 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
AGND
Voltage
Reference
INPUT
FB
11
AAT1149
3MHz Fast Transient 400mA Step-Down Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201987B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
Control Loop
The AAT1149 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 AAT1149 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.
Under-Voltage Lockout
Internal bias of all circuits is controlled via the IN input.
Under-voltage lockout (UVLO) guarantees sufficient VIN
bias and proper operation of all internal circuitry prior to
activation.
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.
Table 1 displays suggested inductor values for various
output voltages.
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 1.8μH CDRH2D09 series inductor selected from
Sumida has a 131mW DCR and a 400mA saturation cur-
rent rating. At full load, the inductor DC loss is 21mW
which gives a 2.8% loss in efficiency for a 400mA, 1.8V
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.
12
AAT1149
3MHz Fast Transient 400mA Step-Down Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201987B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
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 AAT1149. 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.
Confi guration Output Voltage Typical Inductor Value
0.6V Adjustable With External Feedback
1V, 1.2V 1.0μH to 1.2μH
1.5V, 1.8V 1.5μH to 1.8μH
2.5V 2.2μH to 2.7μH
3.3V 3.3μH
Table 1: Inductor Values.
13
AAT1149
3MHz Fast Transient 400mA Step-Down Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201987B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
Figure 1: AAT1149IJS Evaluation Board Figure 2: Exploded View of Evaluation
Top Side. Board Top Side.
Figure 3: AAT1149IJS Evaluation Board
Bottom Side.
14
AAT1149
3MHz Fast Transient 400mA Step-Down Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201987B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
L1 CDRH2D09 or SD3112
L1
C2
4.7μF
C1
4.7μF
U1 AAT1149 SC70JW-8
C1,C2 4.7μF 10V 0805 X5R
VOUT
GND
GND
VIN
1
2
3
Enable
LX
EN
1
FB
2
IN
3
LX
4
AGND
5
PGND
6
PGND
7
PGND
8
AAT1149
U1
R1
R2
59k
C3
C1 10μF 10V 0805 X5R
C3 100pF
Improved Transient Response Version
Figure 4: AAT1149IJS Evaluation Board Schematic.
Figure 5: AAT1149IUV Evaluation Board Figure 6: AAT1149IUV Evaluation Board
Top Side. Bottom Side.
15
AAT1149
3MHz Fast Transient 400mA Step-Down Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201987B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
VIN
VOU
T
C1
4.7μF
C3
L1
U1
WLCSP-5
IN
4
22
1
3
1
5
3
LX
FB
GND
EN
EN AAT1149IUV
C2
4.7μF
R2
59k
R1
adj
Figure 7: AAT1149IUV Evaluation Board Schematic.
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.
Feedback Resistor Selection
Resistors R1 and R2 of Figure 4 program the output to
regulate at a voltage higher than 0.6V. To limit the bias
current required for the external feedback resistor string
while maintaining good noise immunity, the minimum
suggested value for R2 is 59k. Although a larger value
will further reduce quiescent current, it will also increase
the impedance of the feedback node, making it more
sensitive to external noise and interference. Table 2
summarizes the resistor values for various output volt-
ages with R2 set to either 59k for good noise immunity
or 221k for reduced no load input current.
⎛⎞
⎝⎠
R1 = -1 · R2 = - 1 · 59kΩ = 88.5kΩ
VOUT
VREF
⎛⎞
⎝⎠
1.5V
0.6V
The AAT1149, combined with an external feedforward
capacitor (C3 in Figure 4), delivers enhanced transient
response for extreme pulsed load applications. The addi-
tion of the feedforward capacitor typically requires a
larger output capacitor C1 for stability.
VOUT (V)
R2 = 59k
R1 (k)
R2 = 221kW
R1 (k)
0.9 29.4 113K
1.0 39.2 150K
1.1 49.9 187K
1.2 59.0 221K
1.3 68.1 261K
1.4 78.7 301K
1.5 88.7 332K
1.8 118 442K
1.85 124 464K
2.0 137 523K
2.5 187 715K
3.3 267 1.00M
Table 2: Feedback Resistor Values.
16
AAT1149
3MHz Fast Transient 400mA Step-Down Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201987B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
Thermal Calculations
There are three types of losses associated with the
AAT1149 step-down converter: switching losses, conduc-
tion 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.
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 JA for the SC70JW-8 pack-
age which is 160°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 AAT1149 is shown in
Figures 1, 2, and 3. 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 3) and PGND (Pins 6-8).
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 2) should be sepa-
ate 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. If
external feedback resistors are used, they should be
placed as closely as possible to the FB pin (Pin 2) to
minimize the length of the high impedance feedback
trace.
4. The resistance of the trace from the load return to
the PGND (Pins 6-8) 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. A high density, small foot-
print layout can be achieved using an inexpensive,
miniature, non-shielded, high DCR inductor, as
shown in Figure 8.
Figure 8: Minimum Footprint Evaluation Board
Using 2.0x1.25x1.0mm Inductor.
17
AAT1149
3MHz Fast Transient 400mA Step-Down Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201987B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
Step-Down Converter Design Example
Specifications
VO = 1.8V @ 400mA (adjustable using 0.6V version), Pulsed Load DILOAD = 300mA
VIN = 2.7V to 4.2V (3.6V nominal)
FS = 3.0MHz
TAMB = 85°C
1.8V Output Inductor
L1 = 1 ⋅ V
O
= 1 ⋅ 1.8V = 1.8µH
µs
A
µs
A
(use 2.2μH; see Table 1)
For Taiyo Yuden inductor CBC2518T2R2M, 2.2μH, DCR = 130m.
V
O
V
O
1.8
V
1.8V
ΔI
L1
=
⋅ 1 - = ⋅ 1 - = 156m
A
L1 ⋅ F
S
V
IN
2.2µH ⋅ 3.0MHz
4.2V
I
PKL1
= I
O
+ ΔI
L1
= 0.4A + 0.078A = 0.478A
2
P
L1
= I
O
2
⋅ DCR = 0.4A
2
⋅ 130mΩ = 21mW
⎛
⎝⎞
⎠
⎛
⎝⎞
⎠
1.8V Output Capacitor
VDROOP = 0.1V
1
23
1 1.8V · (4.2V - 1.8V)
2.2µH · 3.0MHz · 4.2V
23
RMS
IL1 · FS · VIN(MAX)
= ·
·
3 · ΔILOAD
VDROOP · FS
3 · 0.3A
0.1V · 3.0MHz
COUT = = = 3.0µF; use 4.7µF
· = 45mArms
·
(VO) · (VIN(MAX) - VO)=
Pesr = esr · IRMS2 = 5mΩ · (45mA)2 = 10µW
18
AAT1149
3MHz Fast Transient 400mA Step-Down Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201987B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
Input Capacitor
Input Ripple VPP = 25mV
CIN = = = 1.45µF; use 2.2µF
1
⎛⎞
- ESR · 4 · FS
⎝⎠
VPP
IO
1
⎛⎞
- 5mΩ · 4 · 3.0MHz
⎝⎠
25mV
0.4A
IO
RMS
I
P
= esr · IRMS
2 = 5mΩ · (0.2A)2 = 0.2mW
2
= = 0.2Arms
AAT1149 Losses (SC70JW-8 Package)
PTOTAL
+ (tsw · FS · IO + IQ) · VIN
IO
2 · (RDS(ON)H · VO + RDS(ON)L · [VIN -VO])
VIN
=
=
+ (5ns · 3MHz · 0.4A + 70µA) · 4.2V = 140m
W
0.42 · (0.725Ω · 1.8V + 0.7Ω · [4.2V - 1.8V])
4.2V
TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (160°C/W) · 140mW = 107°C
19
AAT1149
3MHz Fast Transient 400mA Step-Down Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201987B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
Adjustable Version (0.6V device)
VOUT (V)
R2 = 59k1
R1 (k)
R2 = 221k1
R1 (k) L1 (μH)
1.0 39.2 150 1.0
1.2 59.0 221 1.2
1.5 88.7 332 1.5
1.8 118 442 1.8
2.5 187 715 2.2
3.3 267 1000 3.3
Table 3: Evaluation Board Component Values.
Manufacturer Part Number/Type Inductance (μH)
Rated
Current (mA) DCR ()
Size (mm)
LxWxH
Taiyo Yuden
BRC1608
0.77 660 110 0603
(HMAX = 1mm)
1.0 520 180
1.5 410 300
BRL2012
1.5 600 200 0805
(HMAX = 1mm)
2.2 550 250
3.3 450 350
CBC2518
Wire Wound Chip
1.0 1000 80 2.5x1.8x1.8
2.2 890 130
Sumida CDRH2D09
Shielded
1.2 590 97.5
3.2x3.2x1.0
1.5 520 110
1.8 480 131
2.5 440 150
3.0 400 195
Murata LQH2MCN4R7M02
Unshielded
1.0 485 300
2.0x1.6x0.95
1.5 445 400
2.2 425 480
3.3 375 600
Coiltronics SD3118
Shielded
0.68 980 31
3.15x3.15x1.2
0.82 830 54
1.2 720 75
1.5 630 104
2.2 510 116
3.3 430 139
Table 4: 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 5: Surface Mount Capacitors.
1. For reduced quiescent current, R2 = 221k.
20
AAT1149
3MHz Fast Transient 400mA Step-Down Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201987B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
Ordering Information
Output Voltage1Package Marking2Part Number (Tape and Reel)3
0.6; Adj 1.0 SC70JW-8 RGXYY AAT1149IJS-0.6-T1
0.6; Adj 1.0 WLCSP-5 RGYW4AAT1149IUV-0.6-T1
Skyworks Green™ products are compliant with
all applicable legislation and are halogen-free.
For additional information, refer to Skyworks
Definition of Green™, document number
SQ04-0074.
Package Information
SC70JW-8
0.225
±
0.075
0.45
±
0.10
0.05
±
0.05
2.10
±
0.30
2.00
±
0.20
7
°
±
3
°
4
°
±
4
°
1.75
±
0.10
0.85
±
0.15
0.15
±
0.05
1.10 MAX
0.100
2.20
±
0.20
0.048REF
0.50 BSC 0.50 BSC 0.50 BSC
All dimensions in millimeters.
1. Contact Sales for other voltage options.
2. XYY = assembly and date code.
3. Sample stock is generally held on part numbers listed in BOLD.
4. YW = date code (year, week) for WLCSP-5 package.
21
AAT1149
3MHz Fast Transient 400mA Step-Down Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201987B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
Copyright © 2012, 2013 Skyworks Solutions, Inc. All Rights Reserved.
Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. These materials, including the information contained herein, are provided by Skyworks as a
service to its customers and may be used for informational purposes only by the customer. Skyworks assumes no responsibility for errors or omissions in these materials or the information contained herein. Sky-
works may change its documentation, products, services, specifi cations or product descriptions at any time, without notice. Skyworks makes no commitment to update the materials or information and shall have no
responsibility whatsoever for confl icts, incompatibilities, or other diffi culties arising from any future changes.
No license, whether express, implied, by estoppel or otherwise, is granted to any intellectual property rights by this document. Skyworks assumes no liability for any materials, products or information provided here-
under, including the sale, distribution, reproduction or use of Skyworks products, information or materials, except as may be provided in Skyworks Terms and Conditions of Sale.
THE MATERIALS, PRODUCTS AND INFORMATION ARE PROVIDED “AS IS” WITHOUT WARRANTY OF ANY KIND, WHETHER EXPRESS, IMPLIED, STATUTORY, OR OTHERWISE, INCLUDING FITNESS FOR A PARTICULAR
PURPOSE OR USE, MERCHANTABILITY, PERFORMANCE, QUALITY OR NON-INFRINGEMENT OF ANY INTELLECTUAL PROPERTY RIGHT; ALL SUCH WARRANTIES ARE HEREBY EXPRESSLY DISCLAIMED. SKYWORKS DOES
NOT WARRANT THE ACCURACY OR COMPLETENESS OF THE INFORMATION, TEXT, GRAPHICS OR OTHER ITEMS CONTAINED WITHIN THESE MATERIALS. SKYWORKS SHALL NOT BE LIABLE FOR ANY DAMAGES, IN-
CLUDING BUT NOT LIMITED TO ANY SPECIAL, INDIRECT, INCIDENTAL, STATUTORY, OR CONSEQUENTIAL DAMAGES, INCLUDING WITHOUT LIMITATION, LOST REVENUES OR LOST PROFITS THAT MAY RESULT FROM
THE USE OF THE MATERIALS OR INFORMATION, WHETHER OR NOT THE RECIPIENT OF MATERIALS HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
Skyworks products are not intended for use in medical, lifesaving or life-sustaining applications, or other equipment in which the failure of the Skyworks products could lead to personal injury, death, physical or en-
vironmental damage. Skyworks customers using or selling Skyworks products for use in such applications do so at their own risk and agree to fully indemnify Skyworks for any damages resulting from such improper
use or sale.
Customers are responsible for their products and applications using Skyworks products, which may deviate from published specifi cations as a result of design defects, errors, or operation of products outside of pub-
lished parameters or design specifi cations. Customers should include design and operating safeguards to minimize these and other risks. Skyworks assumes no liability for applications assistance, customer product
design, or damage to any equipment resulting from the use of Skyworks products outside of stated published specifi cations or parameters.
Skyworks, the Skyworks symbol, and “Breakthrough Simplicity” are trademarks or registered trademarks of Skyworks Solutions, Inc., in the United States and other countries. Third-party brands and names are for
identifi cation purposes only, and are the property of their respective owners. Additional information, including relevant terms and conditions, posted at www.skyworksinc.com, are incorporated by reference.
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