1
AAT2146
Low-Noise, Fast Transient 600mA Step-Down Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202007A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 25, 2012
General Description
The AAT2146 SwitchReg is a 2MHz step-down converter
with an input voltage range of 2.7V to 5.5V and output
voltage as low as 0.6V. It is optimized to react quickly to
a load variation. The AAT2146 incorporates a unique low
noise architecture which reduces ripple and spectral
noise.
The AAT2146 is available in fixed voltage versions with
internal feedback and a programmable version with
external feedback resistors. It can deliver 600mA of load
current while maintaining a low 37μA no load quiescent
current. The 2MHz switching frequency minimizes the
size of external components while keeping switching
losses low.
The AAT2146 is designed to maintain high efficiency
throughout the operating range, which is critical for por-
table applications.
The AAT2146 is available in the Pb-free, space-saving
2.0x2.1mm SC70JW-8 package and is rated over the
-40°C to +85°C temperature range.
Features
• VIN Range: 2.7V to 5.5V
• Low Noise Light Load Mode
• Low Ripple PWM Mode
• VOUT Fixed or Adjustable from 0.6V to VIN
• 37μA No Load Quiescent Current
• Up to 98% Efficiency
• 600mA Max Output Current
• 2MHz Switching Frequency
• 150μs Soft Start
• Fast Load Transient
• Over-Temperature Protection
• Current Limit Protection
• 100% Duty Cycle Low-Dropout Operation
• <1μA Shutdown Current
• SC70JW-8 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 (Fixed Output Voltage)
4.7µH
L1
4.7µF
C1
2.2µF
C2 EN OUT
VIN LX
AGND
PGND
PGND
PGND
AAT2146
U1
VIN VO
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2
AAT2146
Low-Noise, Fast Transient 600mA Step-Down Converter
DATA SHEET
Pin Descriptions
Pin # Symbol Function
1 EN Enable pin.
2 OUT Feedback input pin. This pin is connected either directly to the converter output or to an external
resistive divider for an adjustable output.
3 VIN Input supply voltage for the converter.
4LX
Switching node. Connect the inductor to this pin. It is internally connected to the drain of both
high- and low-side MOSFETs.
5 AGND 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
(Top View)
OUT
VIN
LX
PGND
PGND
PGND
AGND
EN 1
2
3
45
6
7
8
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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AAT2146
Low-Noise, Fast Transient 600mA Step-Down Converter
DATA SHEET
Absolute Maximum Ratings1
Symbol Description Value Units
VIN Input Voltage GND 6.0 V
VLX LX to GND -0.3 to VIN + 0.3 V
VOUT OUT to GND -0.3 to VIN + 0.3 V
VEN EN to GND -0.3 to VIN + 0.3 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, 3 625 mW
JA Thermal Resistance2 160 °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.
3. Derate 6.25mW/°C above 25°C.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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4
AAT2146
Low-Noise, Fast Transient 600mA Step-Down Converter
DATA SHEET
Electrical Characteristics1
TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C, VIN = 3.6V.
Symbol Description Conditions Min Typ Max Units
Step-Down Converter
VIN Input Voltage 2.7 5.5 V
VUVLO UVLO Threshold
VIN Rising 2.7 V
Hysteresis 100 mV
VIN Falling 1.8 V
VOUT Output Voltage Tolerance IOUT = 0mA to 600mA, VIN = 2.7V to 5.5V -3.0 +3.0 %
VOUT Output Voltage Range 0.6 VIN V
IQQuiescent Current No Load, 0.6V Adjustable Version 37 70 μA
ISHDN Shutdown Current EN = AGND = PGND 1.0 μA
ILIM P-Channel Current Limit 800 mA
RDS(ON)H High Side Switch On Resistance 0.35
RDS(ON)L Low Side Switch On Resistance 0.30
VLinereg Line Regulation VIN = 2.7V to 5.5V; IOUT = 600mA 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
ROUT Out Impedance >0.6V Output 250 k
TSStart-Up Time From Enable to Output Regulation 150 μs
FOSC Oscillator Frequency TA = 25°C 0.9 2.0 2.6 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 AAT2146 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.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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AAT2146
Low-Noise, Fast Transient 600mA Step-Down Converter
DATA SHEET
Typical Characteristics
Efficiency vs. Output Current
(VOUT = 1.8V)
Output Current
(mA)
Efficiency (%)
30
40
50
60
70
80
90
100
0.1 1 10 100 1000
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
Load Regulation
(VOUT = 1.8V)
Output Current
(mA)
Output Error (%)
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
0.1 1 10 100 1000
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
Efficiency vs. Output Current
(VOUT = 2.5V)
Output Current
(mA)
Efficiency (%)
30
40
50
60
70
80
90
100
0.1 1 10 100 1000
VIN = 3V
VIN = 3.6V
VIN = 4.2V
VIN = 5V
Load Regulation
(VOUT = 2.5V)
Output Current
(mA)
Output Error (%)
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
0.1 1 10 100 1000
VIN = 3V
VIN = 3.6V
VIN = 4.2V
VIN = 5V
Efficiency vs. Output Current
(VOUT = 3.3V)
Output Current
(mA)
Efficiency (%)
30
40
50
60
70
80
90
100
0.1 1 10 100 1000
VIN = 3.6V
VIN = 4.2V
VIN = 5V
Load Regulation
(VOUT = 3.3V)
Output Current
(mA)
Output Error (%)
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
0.1 1 10 100 1000
VIN = 3.6V
VIN = 4.2V
VIN = 5V
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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6
AAT2146
Low-Noise, Fast Transient 600mA Step-Down Converter
DATA SHEET
Typical Characteristics
Line Regulation
(VOUT = 1.8V)
Input Voltage (V)
Accuracy (%)
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
1mA
400mA
600mA
Switching Frequency vs. Temperature
(VOUT = 1.8V; IOUT = 1A)
Input Voltage (V)
Switching Frequency (MHz)
1.92
1.94
1.96
1.98
2
2.02
2.04
2.06
2.08
-40 -15 10 35 60 85
Frequency Variation vs. Input Voltage
Input Voltage (V)
Frequency Variation (%)
-4
-3
-2
-1
0
1
2
3
4
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
VOUT = 1.8V
VOUT = 3V
Output Voltage Error vs. Temperature
(VIN = 3.6V; VO = 1.8V, IOUT = 400mA)
Temperature (°C)
Output Voltage Error (%)
-2.0
-1.0
0.0
1.0
2.0
-40 -20 0 20 40 60 80 10
0
No Load Quiescent Current vs. Input Voltage
Input Voltage (V)
Supply Current (µA)
10
15
20
25
30
35
40
45
50
55
60
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
85°C
25C
-40°C
P-Channel RDS(ON) vs. Input Voltage
Input Voltage (V)
RDS(ON) (mΩ
Ω
)
200
250
300
350
400
450
500
550
2.5 3 3.5 4 4.5 5 5.5 6
120°C
100°C
85°C
25°C
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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AAT2146
Low-Noise, Fast Transient 600mA Step-Down Converter
DATA SHEET
Typical Characteristics
N-Channel RDS(ON) vs. Input Voltage
Input Voltage (V)
RDS(ON) (mΩ
Ω
)
200
250
300
350
400
450
500
550
2.5 3 3.5 4 4.5 5 5.5 6
120°C
100°C
85°C
25°C
Load Transient
(VIN = 3.6V; VOUT = 1.8V; COUT = 10µF; CFF = 100pF)
Time (50µs/div)
Output Voltage (top) (V)
Output and Inductor Current
(100mA/div)
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
300mA
1mA
300mA
1mA
Load Transient
(VIN = 3.6V; VOUT = 1.8V; COUT = 4.7µF; CFF = 0pF)
Time (50µs/div)
Output Voltage (top) (V)
Output and Inductor Current
(100mA/div)
1.5
1.55
1.6
1.65
1.7
1.75
1.8
1.85
400mA 300mA
400mA
300mA
Load Transient
(VIN = 3.6V; VOUT = 1.8V; COUT = 10µF; CFF = 0pF)
Time (50µs/div)
Output Voltage (top) (V)
Output and Inductor Current
(100mA/div)
1.5
1.55
1.6
1.65
1.7
1.75
1.8
1.85
400mA
400mA
300mA
300mA
Load Transient
(VIN = 3.6V; VOUT = 1.8V; COUT = 10µF; CFF = 100pF)
Time (50µs/div)
Output Voltage (top) (V)
Output and Inductor Current
(100mA/div)
1.5
1.55
1.6
1.65
1.7
1.75
1.8
1.85
400mA 300mA
400mA
300mA
Line Transient
(VOUT = 1.8V; VIN = 3.6V to 4.2V; IOUT = 400mA; CFF = 0pF)
Time (50µs/div)
Input Voltage (top) (V)
Output Voltage (bottom) (V)
0
0.6
1.2
1.8
2.4
3
3.6
4.2
4.8
1.76
1.78
1.8
1.82
1.84
1.86
1.88
1.9
1.92
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8
AAT2146
Low-Noise, Fast Transient 600mA Step-Down Converter
DATA SHEET
Typical Characteristics
Output Ripple
(VOUT = 1.8V; VIN = 3.6V; IOUT = 1mA; CFF = 0pF)
Time (10µs/div)
Output Voltage (top) (V)
Inductor Current
(bottom) (A)
-0.06
-0.05
-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Output Ripple
(VOUT = 1.8V; VIN = 3.6V; IOUT = 400mA; CFF = 0pF)
Time (200ns/div)
Output Voltage (top) (V)
Inductor Current
(bottom) (A)
-0.06
-0.05
-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
Soft Start
(VIN = 3.6V; VOUT = 1.8V; IOUT = 400mA)
Time (100µs/div)
Enable Voltage (top) (V)
Output Voltage (middle) (V)
Input Current (bottom) (A)
0
1
2
3
4
-0.5
0
0.5
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AAT2146
Low-Noise, Fast Transient 600mA Step-Down Converter
DATA SHEET
Functional Description
The AAT2146 is a high performance 600mA 2MHz mono-
lithic step-down converter. It has been designed with the
goal of minimizing external component size and optimiz-
ing efficiency over the complete load range, and pro-
duces reduced ripple and spectral noise. Apart from the
small bypass input capacitor, only a small L-C filter is
required at the output. Typically, a 4.7μH inductor and a
4.7μF ceramic capacitor are recommended (see table of
values).
The fixed output version requires only three external
power components (CIN, COUT
, and L). The adjustable ver-
sion can be programmed with external feedback to any
voltage, ranging from 0.6V to the input voltage. An addi-
tional feed-forward capacitor can also be added to the
external feedback to provide improved transient response
(see Figure 1).
At dropout, the converter duty cycle increases to 100%
and the output voltage tracks the input voltage minus
the RDSON 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 600mA.
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
VIN
OUT
AGND
Voltage
Reference
INPUT
See note
Note: For adjustable version, the internal feedback divider is omitted and the OUT pin is tied directly
to the internal error amplifier.
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10
AAT2146
Low-Noise, Fast Transient 600mA Step-Down Converter
DATA SHEET
Control Loop
The AAT2146 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
fixed voltage versions, the error amplifier reference volt-
age is internally set to program the converter output
voltage. 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 AAT2146 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 VIN input.
Under-voltage lockout (UVLO) guarantees sufficient VIN
bias and proper operation of all internal circuitry prior to
activation.
L1 CDRH3D16-4R7
4.7µH
L1
10µF
C1
4.7µF
C2
U1 AAT2146 SC70JW-8
C1 10µF 10V 0805 X5R
C2 4.7µF 10V 0805 X5R
CFF 100pF 0402 X5R
VOUT
GND
VIN
CFF
1
2
3
Enable
LX
EN
1
OUT
2
VIN
3
LX
4AGND 5
PGND 6
PGND 7
PGND 8
AAT2146
U1
GND2
118k
R1
59k
R2
Figure 1: Enhanced Transient Response Schematic.
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AAT2146
Low-Noise, Fast Transient 600mA Step-Down Converter
DATA SHEET
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.
The internal slope compensation for the adjustable and
low-voltage fixed versions of the AAT2146 is 0.24A/μs.
This equates to a slope compensation that is 75% of the
inductor current down slope for a 1.5V output and 4.7μH
inductor.
0.75 ⋅ V
O
m = = = 0.24
L
0.75 ⋅ 1.5V
4.7µH
A
µs
This is the internal slope compensation for the adjust-
able (0.6V) version or low-voltage fixed versions. When
externally programming the 0.6V version to 2.5V, the
calculated inductance is 7.5μH.
0.75 ⋅ V
O
L = =
≈
3 ⋅ V
O
= 3 ⋅ 2.5V = 7.5µH
m
0.75
⋅
V
O
0.24A
µs
A
µs
A
A
µs
In this case, a standard 6.8μH value is selected.
For high-voltage fixed versions (2.5V), m = 0.48A/μs.
Table 1 displays inductor values for the AAT2146 fixed
and adjustable options.
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 4.7μH CDRH3D16 series inductor selected from
Sumida has a 105m DCR and a 900mA DC current rat-
ing. At full load, the inductor DC loss is 17mW which
gives a 2.8% loss in efficiency for a 400mA, 1.5V out-
put.
Input Capacitor
Select a 2.2μF 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 volt-
age 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
ceramic capacitor with 5.0V DC applied is actually about
6μF.
Confi guration Output Voltage Inductor
0.6V Adjustable With
External Feedback
1V, 1.2V 2.2μH
1.5V, 1.8V 4.7μH
2.5V, 3.3V 6.8μH
Fixed Output 0.6V to 3.3V 4.7μH
Table 1: Inductor Values.
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
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12
AAT2146
Low-Noise, Fast Transient 600mA Step-Down Converter
DATA SHEET
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 AAT2146. 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 2.
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
dominated by the capacitance of the ceramic output
capacitor. 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 rela-
tionship of the output voltage droop during the three
switching cycles to the output capacitance can be esti-
mated 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 · F · 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.
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AAT2146
Low-Noise, Fast Transient 600mA Step-Down Converter
DATA SHEET
Adjustable Output Resistor Selection
For applications requiring an adjustable output voltage,
the 0.6V version can be externally programmed. Resistors
R1 and R2 of Figure 5 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 sug-
gested 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 sensi-
tive to external noise and interference. Table 2 summa-
rizes the resistor values for various output voltages 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 adjustable version of the AAT2146, combined with
an external feedforward capacitor (C4 in Figure 1),
delivers enhanced transient response for extreme pulsed
load applications. The addition of the feedforward capac-
itor typically requires a larger output capacitor C1 for
stability.
Figure 2: AAT2146 Evaluation Board Figure 3: Exploded View of AAT2146
Component Side Layout. Evaluation Board Component Side Layout.
Figure 4: AAT2146 Evaluation Board
Solder Side Layout.
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14
AAT2146
Low-Noise, Fast Transient 600mA Step-Down Converter
DATA SHEET
VOUT (V)
R2 = 59kR2 = 221k
R1 (k)R1
0.8 19.6 75K
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: Adjustable Resistor Values For Use With
0.6V Step-Down Converter.
Thermal Calculations
There are three types of losses associated with the
AAT2146 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
switching devices. At full load, assuming continuous con-
duction mode (CCM), a simplified form of the losses is
given by:
PTOTAL
IO
2 · (RDSON(HS) · VO + RDSON(LS) · [VIN - VO])
VIN
=
+ (tsw · F · 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 · RDSON(HS) + 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
L1 CDRH3D16-4R7
4.7μH
L1
10μF
C1
4.7μF
C2
U1 AAT2146 SC70JW-8
C2 4.7μF 10V 0805 X5R
VOUT =1.8V
GND
VIN
1
2
3
Enable
LX
EN
1
OUT
2
VIN
3
LX
4AGND 5
PGND 6
PGND 7
PGND 8
AAT2146
U1
GND2
118k
R1
59k
R2
C1 10μF 6.3V 0805 X5R
100pF
C4
n/a
C3
Figure 5: AAT2146 Adjustable Evaluation Board Schematic.
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AAT2146
Low-Noise, Fast Transient 600mA Step-Down Converter
DATA SHEET
Layout
The suggested PCB layout for the AAT2146 is shown in
Figures 2, 3, and 4. The following guidelines should be
used to help ensure a proper layout.
1. The input capacitor (C2) should connect as closely
as possible to VIN (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 OUT pin (Pin 2) should be
separate 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 regu-
lation. If external feedback resistors are used, they
should be placed as closely as possible to the OUT
pin (Pin 2) to minimize the length of the high imped-
ance 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.
A high density, small footprint layout can be achieved
using an inexpensive, miniature, non-shielded, high DCR
inductor. An evaluation board is available with this
inductor and is shown in Figure 6. The total solution
footprint area is 40mm2.
Figure 6: Minimum Footprint Evaluation Board
Using 2.0mm x 1.6mm x 0.95mm Inductor.
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16
AAT2146
Low-Noise, Fast Transient 600mA Step-Down Converter
DATA SHEET
Step-Down Converter Design Example
Specifications
VO = 1.8V @ 400mA (adjustable using 0.6V version), Pulsed Load ILOAD = 300mA
VIN = 2.7V to 4.2V (3.6V nominal)
FS = 2MHz
TAMB = 85°C
1.8V Output Inductor
L1 = 3 ⋅ V
O2
= 3 ⋅ 1.8V = 5.4µH
µs
A
µs
A
(use 4.7μH; see Table 1)
For Sumida inductor CDRH3D16, 4.7μH, DCR = 105m.
V
O
V
O
1.8
V
1.8V
ΔI
L1
=
⋅ 1 - = ⋅ 1 - = 109m
A
L1 ⋅ F
S
V
IN
4.7µH ⋅ 2.0MHz
4.2V
I
PKL1
= I
O
+ ΔI
L1
= 0.4A + 0.055A = 0.455A
2
P
L1
= I
O
2
⋅ DCR = 0.4A
2
⋅ 105mΩ = 17mW
⎛
⎝⎞
⎠
⎛
⎝⎞
⎠
1.8V Output Capacitor
VDROOP = 0.1V
1
23
1 1.8V · (4.2V - 1.8V)
4.7µH · 2.0MHz · 4.2V
23
RMS
IL1 · F · VIN(MAX)
= ·
·
3 · ΔILOAD
VDROOP · FS
3 · 0.3A
0.1V · 2.0MHz
COUT = = = 4.5µF; use 4.7µF
· = 32mArms
·
(VO) · (VIN(MAX) - VO)=
Pesr = esr · IRMS2 = 5mΩ · (32mA)2 = 6µW
Input Capacitor
Input Ripple VPP = 25mV
CIN = = = 2.17µF; use 2.2µF
1
⎛⎞
- ESR · 4 · FS
⎝⎠
VPP
IO
1
⎛⎞
- 5mΩ · 4 · 2.0MHz
⎝⎠
25mV
0.4A
IO
RMS
I
P = esr · IRMS
2 = 5mΩ · (0.2A)2 = 0.2mW
2
= = 0.2Arms
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AAT2146
Low-Noise, Fast Transient 600mA Step-Down Converter
DATA SHEET
AAT2146 Losses
PTOTAL
+ (tsw · F · IO + IQ) · VIN
IO
2 · (RDSON(HS) · VO + RDSON(LS) · [VIN -VO])
VIN
=
=
+ (5ns · 2.0MHz · 0.4A + 70µA) · 4.2V = 131mW
0.42 · (0.725Ω · 1.8V + 0.7Ω · [4.2V - 1.8V])
4.2V
TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (160°C/W) · 131mW = 105.9°C
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18
AAT2146
Low-Noise, Fast Transient 600mA Step-Down Converter
DATA SHEET
Adjustable Version
(0.6V device)
VOUT (V)
R2 = 59k
R1 (k)
R2 = 221k1
R1 (k) L1 (μH)
0.8 19.6 75.0 2.2
0.9 29.4 113 2.2
1.0 39.2 150 2.2
1.1 49.9 187 2.2
1.2 59.0 221 2.2
1.3 68.1 261 2.2
1.4 78.7 301 4.7
1.5 88.7 332 4.7
1.8 118 442 4.7
1.85 124 464 4.7
2.0 137 523 6.8
2.5 187 715 6.8
3.3 267 1000 6.8
Fixed Version
VOUT (V)
R2, R4 Not Used
R1 (k) L1 (μH)
0.6-3.3V 0 4.7
Table 3: Evaluation Board Component Values.
Manufacturer Part Number Inductance (μH)
Max DC
Current (A) DCR ()
Size (mm)
LxWxH Type
Sumida
CDRH3D16-2R2 2.2 1.20 0.072 3.8x3.8x1.8 Shielded
CDRH3D16-4R7 4.7 0.90 0.105 3.8x3.8x1.8 Shielded
CDRH3D16-6R8 6.8 0.73 0.170 3.8x3.8x1.8 Shielded
Murata LQH2MCN4R7M02 4.7 0.40 0.80 2.0x1.6x0.95 Non-Shielded
LQH32CN4R7M23 4.7 0.45 0.20 2.5x3.2x2.0 Non-Shielded
Coilcraft LPO3310-472 4.7 0.80 0.27 3.2x3.2x1.0 1mm
Coiltronics
SD3118-4R7 4.7 0.98 0.122 3.1x3.1x1.85 Shielded
SD3118-6R8 6.8 0.82 0.175 3.1x3.1x1.85 Shielded
SDRC10-4R7 4.7 1.30 0.122 5.7x4.4x1.0 1mm Shielded
TDK VLS3015T-4R7MR99 4.7 0.99 0.136 3.0x3.0x1.5 Shielded
VLS3015T-6R8MR86 6.8 0.86 0.176 3.0x3.0x1.5 Shielded
Wurth 744042006 6.8 1.25 0.100 4.8x4.8x1.8 Shielded
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 GRM21BR60J226ME39 22μF 6.3V X5R 0805
Table 5: Surface Mount Capacitors.
1. For reduced quiescent current, R2 and R4 = 221k.
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AAT2146
Low-Noise, Fast Transient 600mA Step-Down Converter
DATA SHEET
Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved.
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Ordering Information
Output Voltage1Package Marking2Part Number (Tape and Reel)3
Adj 0.6 SC70JW-8 YXXYY AAT2146IJS-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 typically held on part numbers listed in BOLD.
