1
AAT1154
1MHz 3A Step-Down DC/DC Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201993A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
General Description
The AAT1154 SwitchReg is a step-down switching con-
verter ideal for applications where high efficiency, small
size, and low ripple are critical. Able to deliver 3A with
an internal power MOSFET, the current-mode controlled
IC provides high efficiency. Fully internally compensated,
the AAT1154 simplifies system design and lowers exter-
nal parts count.
The AAT1154 is available in a Pb-free SOP-8 package and
is rated over the -40°C to +85°C temperature range.
Features
• VIN Range: 2.7V to 5.5V
• Fixed or Adjustable VOUT: 1.0V to 4.2V
• 3A Output Current
• Up to 95% Efficiency
• Integrated Low On Resistance Power Switch
• Internally Compensated Current Mode Control
• 1MHz Switching Frequency
• Constant Pulse Width Modulation (PWM) Mode
• Low Output Ripple With Light Load
• Internal Soft Start
• Current Limit Protection
• Over-Temperature Protection
• SOP-8 Package
• -40°C to +85°C Temperature Range
Applications
• Cable/DSL Modems
• Computer Peripherals
• High Efficiency Conversion from 5V or 3.3V Supply
• Network Cards
• Set-Top Boxes
Typical Application
OUTPUT
INPUT
1.5μH
120μF
LX
VP
FB
GND
AAT1154
VCC
EN
10μF
0.1μF
100Ω
2
AAT1154
1MHz 3A Step-Down DC/DC Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201993A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
Pin Descriptions
Pin # Symbol Function
1FB
Feedback input pin. This pin must be connected to the converter output. It is used to set the converter
output to regulate to the desired value.
2 GND Ground connection.
3EN
Enable input pin. When connected high, the AAT1154 is in normal operation; when connected low, it is
powered down. This pin should not be left fl oating.
4 VCC Power supply: supplies power for the internal circuitry.
5, 8 VP Input supply voltage for converter power stage.
6, 7 LX Inductor connection pins. These pins should be connected to the output inductor. Internally, Pins 6 and 7
are connected to the drain of the P-channel switch.
Pin Configuration
SOP-8
LX
VP
LX
VP
FB
GND
EN
VCC
1
2
3
4
8
7
6
5
3
AAT1154
1MHz 3A Step-Down DC/DC Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201993A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
Absolute Maximum Ratings1
TA = 25°C, unless otherwise noted.
Symbol Description Value Units
VCC, VPVCC, VP to GND 6V
VLX LX to GND -0.3 to VP + 0.3 V
VFB FB to GND -0.3 to VCC + 0.3 V
VEN EN to GND -0.3 to VCC + 0.3 V
TJOperating Junction Temperature Range -40 to 150 °C
VESD ESD Rating2 - HBM 3000 V
Thermal Characteristics3
Symbol Description Value Units
JA Thermal Resistance 110 °C/W
PDMaximum Power Dissipation (TA = 25°C)4909 mW
Recommended Operating Conditions
Symbol Description Value Units
T Ambient Temperature Range -40 to +85 °C
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. Human body model is a 100pF capacitor discharged through a 1.5k resistor into each pin.
3. Mounted on a demo board (FR4, in still air).
4. Derate 9.1mW/°C above 25°C.
4
AAT1154
1MHz 3A Step-Down DC/DC Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201993A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
Electrical Characteristics
VIN = VCC = VP = 5V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = 25°C.
Symbol Description Conditions Min Typ Max Units
VIN Input Voltage Range 2.7 5.5 V
VOUT Output Voltage Tolerance VIN = VOUT + 0.2V to 5.5V, IOUT = 0A to 3A -5.0 5.0 %
VUVLO Under-Voltage Lockout VIN Rising 2.5 V
VIN Falling 1.2
VUVLO(HYS) Under-Voltage Lockout Hysteresis 250 mV
IQQuiescent Supply Current No Load, VFB = 0V 630 1000 μA
ISHDN Shutdown Current VEN = 0V, VIN = 5.5V 1.0 μA
ILIM Current Limit TA = 25°C 4.4 A
RDS(ON)H High Side Switch On Resistance TA = 25°C 60 m
Effi ciency IOUT = 1A 92 %
VLOADREG Load Regulation ILOAD = 0A to 3A 2.6 %
VLINEREG/
VIN
Line Regulation VIN = 2.7V to 5.5V 0.75 %/V
FOSC Oscillator Frequency TA = 25°C 1 MHz
VEN(L) Enable Threshold Low 0.6 V
VEN(H) Enable Threshold High 1.4 V
TSD Over-Temperature Shutdown Threshold 140 °C
THYS Over-Temperature Shutdown Hysteresis 15 °C
5
AAT1154
1MHz 3A Step-Down DC/DC Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201993A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
Typical Characteristics
Efficiency vs. Load Current
(V
IN
= 5V; V
OUT
= 3.3V)
60
65
70
75
80
85
90
95
100
0.01 0.1 1 10
Output Current (A)
Efficiency (%)
RDS(ON) vs. Temperature
40
50
60
70
80
90
-20 0 20 40 60 80 100 120
Temperature (°C)
RDS(ON) (mΩ)
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
VIN = 5V
VIN = 5.5V
Oscillator Frequency Variation vs.
Supply Voltage
-0.5
-0.25
0
0.25
0.5
3.5 4 4.5 5 5.5
Input Voltage (V)
Variation (%)
R
DS(ON)
vs. V
IN
(I
DS
= 1A)
40
45
50
55
60
65
70
2.5 3 3.5 4 4.5 5 5.5
Input Voltage (V)
R
DS(ON)
(mΩ
)
Oscillator Frequency Variation vs. Temperature
(V
IN
= 5V)
-4
-3
-2
-1
0
1
-20 0 20 40 60 80 100
Temperature (°C)
Variation (%)
Enable Threshold vs. Input Voltage
0.6
0.7
0.8
0.9
1
1.1
1.2
2.5 3 3.5 4 4.5 5 5.5
Input Voltage (V)
Enable Threshold (V)
EN(H)
EN(L)
6
AAT1154
1MHz 3A Step-Down DC/DC Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201993A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
Typical Characteristics
Output Voltage vs. Temperature
(IOUT = 2A)
-20 0 20 40 60 80 100
Temperature (°
°
C)
Variation (%)
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
Line Regulation
(VOUT = 3.3V)
-5
-4
-3
-2
-1
0
1
3 3.5 4 4.5 5 5.5 6
Input Voltage (V)
Output Voltge Error (%)
IO = 0.3A
IO = 3.0A
Over-Temperature Current vs. Input Voltage
(VOUT = 3.3V)
2
2.2
2.4
2.6
2.8
3
3.2
3.4
3.6
3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5
Input Voltage (V)
Output Current (A)
100°C
70°C
85°C
Load Regulation
(VIN = 5.0V; VIN = 3.3V)
-10.0
-9.0
-8.0
-7.0
-6.0
-5.0
-4.0
-3.0
-2.0
-1.0
0.0
0.01 0.1 1 10
Load Current (A)
Output Error (%)
Non-Switching Operating Current vs. Temperature
(FB = 0V)
0.4
0.5
0.6
0.7
0.8
-20 0 20 40 60 80 100 120
Temperature (
°
C)
Operating Current (mA)
V
IN
= 5.5V
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 5.0V
Over-Temperature Shutdown
Current vs. Temperature
(VOUT = 3.3V; VIN = 5.0V; L = 1.5
μ
H)
2
2.5
3
3.5
4
4.5
5
5.5
6
10 20 30 40 50 60 70 80 90 100
Temperature (
°
C)
Output Current (A)
7
AAT1154
1MHz 3A Step-Down DC/DC Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201993A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
Typical Characteristics
Inrush and Output Overshoot Characteristics
(3A Load)
-2
0
2
4
6
8
10
12
14
0 0.4 0.8 1.2 1.6 2
Time (ms)
Voltage (V)
(bottom traces)
-10
-8
-6
-4
-2
0
2
4
6
Inductor Current (A)
(top trace)
Inductor Current
Output
Input
Inrush and Output Overshoot Characteristics
(No Load)
-2
0
2
4
6
8
10
12
14
0 0.4 0.8 1.2 1.6 2
Time (ms)
Voltage (V)
(bottom traces)
-10
-8
-6
-4
-2
0
2
4
6
Inductor Current (A)
(top trace)
Inductor Current
Output
Input
Output Ripple
(IOUT = 3.0A; VOUT = 3.3V; VIN = 5.0V)
-12
-10
-8
-6
-4
-2
0
2
4
0 12345
Time (μ
μ
s)
AC Output Ripple
top (mV)
-1
0
1
2
3
4
5
6
7
Inductor Current
(bottom) (A)
300µF 6.3VCeramic
TDK P/N C3325X5R0J107M
Output Ripple
(IOUT = 3.0A; VOUT = 3.3V; VIN = 5.0V)
-12
-10
-8
-6
-4
-2
0
2
4
0 12345
AC Output Ripple
(top) (mV)
-1
0
1
2
3
4
5
6
7
Inductor Current
(bottom) (A)
Time (μ
μ
s)
200μF 6.3V Ceramic
TDK P/N C3325X5R0J107M
Tantalum Output Ripple
(IOUT = 3.0A; VOUT = 3.3V; VIN = 5.0V)
-120
-100
-80
-60
-40
-20
0
20
40
012345
Time (μ
μ
s)
AC Output Ripple (top)
(mV)
-1
0
1
2
3
4
5
6
7
Inductor Current
(bottom) (A)
120μF 6.3V Tantalum Vishay
P/N 594D127X96R3C2T
Loop Crossover Gain and Phase
-16
-12
-8
-4
0
4
8
12
16
10000 100000
Frequency (Hz)
Gain (dB)
-180
-135
-90
-45
0
45
90
135
180
Phase (degrees)
100μF 6.3V Ceramic
TDK P/N C3225X5R0J107M
Phase
3x 100μF
2x 100μF
8
AAT1154
1MHz 3A Step-Down DC/DC Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201993A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
Typical Characteristics
Loop Crossover Gain and Phase
-16
-12
-8
-4
0
4
8
12
16
10000 100000
Frequency (Hz)
Gain (dB)
-180
-135
-90
-45
0
45
90
135
180
Phase (degrees)
120μF 6.3V Tantalum
Vishay P/N 594D127X96R3C2T
Phase
Gain
Transient Response
(IOUT = 0 to 3.0A; VOUT = 3.3V; VIN = 5.0V)
Time (μ
μ
s)
Output Voltage
(top) (mV)
Inductor Current
(bottom) (A)
-700
-600
-500
-400
-300
-200
-100
0
100
0 100 200 300 400 500
-1
0
1
2
3
4
5
6
7
3x 100μF 6.3V Ceramic
TDK P/N C3325X5R0J107M
Transient Response
(IOUT = 0 to 3.0A; VOUT = 3.3V; VIN = 5.0V)
Time (μ
μ
s)
Output Voltage
(top) (mV)
Inductor Current
(bottom) (A)
-700
-600
-500
-400
-300
-200
-100
0
100
0 100 200 300 400 500
-1
0
1
2
3
4
5
6
7
2x 100μF 6.3V Ceramic
TDK P/N C3325X5R0J107M
Tantalum Transient Response
(IOUT = 0 to 3.0A; VOUT = 3.3V; VIN = 5.0V)
-700
-600
-500
-400
-300
-200
-100
0
100
0 100 200 300 400 500
Time (μ
μ
s)
Output Voltage
(top) (mV)
-1
0
1
2
3
4
5
6
7
Inductor Current
(bottom) (A)
120μF 6.3V Tantalum
Vishay P/N 594D127X96R3C2T
9
AAT1154
1MHz 3A Step-Down DC/DC Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201993A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
Applications Information
Main Control Loop
The AAT1154 is a peak current mode step-down con-
verter. The inner wide bandwidth loop controls the
inductor peak current. The inductor current is sensed as
it flows through the internal P-channel MOSFET. A fixed
slope compensation signal is then added to the sensed
current to maintain stability for duty cycles greater than
50%. The inner loop appears as a voltage-programmed
current source in parallel with the output capacitor.
The voltage error amplifier output programs the current
loop for the necessary inductor current to force a con-
stant output voltage for all load and line conditions. The
feedback resistive divider is internal, dividing the output
voltage to the error amplifier reference voltage of 1V.
The error amplifier has a limited DC gain. This eliminates
the need for external compensation components, while
still providing sufficient DC loop gain for good load regu-
lation. The crossover frequency and phase margin are
set by the output capacitor value.
Duty cycle extends to 100% as the input voltage
approaches the output voltage. Thermal shutdown pro-
tection disables the device in the event of a short-circuit
or overload condition.
Soft Start/Enable
Soft start controls the current limit when the input volt-
age or enable is applied. It limits the current surge seen
at the input and eliminates output voltage overshoot.
When pulled low, the enable input forces the device into
a low-power, non-switching state. The total input current
during shutdown is less than 1μA.
Power and Signal Source
Separate small signal ground and power supply pins iso-
late the internal control circuitry from switching noise. In
Functional Block Diagram
VP = 2.7V to 5.5V
ENGND
LOGIC
REF
Temp.
Sensing
OSC
OP. AMP
VCC
LX
FB DH
CMP
10
AAT1154
1MHz 3A Step-Down DC/DC Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201993A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
addition, the low pass filter R1 and C3 (shown in Figure
1) filters noise associated with the power switching.
Current Limit and
Over-Temperature Protection
Over-temperature and current limit circuitry protects the
AAT1154 and the external Schottky diode during over-
load, short-circuit, and excessive ambient temperature
conditions. The junction over-temperature threshold is
140°C nominal and has 15°C of hysteresis. Typical
graphs of the over-temperature load current vs. input
voltage and ambient temperature are shown in the
Typical Characteristics section of this document.
Inductor
The output inductor is selected to limit the ripple current
to 20% to 40% of full load current at the maximum input
voltage. 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
inductor saturation characteristics. The inductor should
not show any appreciable saturation under normal load
conditions. During overload and short-circuit conditions,
the inductor can exceed its peak current rating without
affecting converter performance. Some inductors may
have sufficient peak and average current ratings yet
result in excessive losses due to a high DC resistance
(DCR). The losses associated with the DCR and its effect
on the total converter efficiency must be considered.
For a 3A load and the ripple current set to 30% at the
maximum input voltage, the maximum peak-to-peak
ripple current is 0.9A. Assuming a 5V ±5% input voltage
and 30% ripple, the output inductance required is:
L = · 1 -
VOUT VOUT
IOUT · k · FS VIN(MAX)
= · 1 -
3.3V
3.3V
3A · 0.3 · 1MHz 5.25V
⎛⎞
⎝⎠
⎛⎞
⎛⎞
⎝⎠
⎝⎠
= 1.36μH
The factor “k” is the fraction of the full load (30%)
selected for the ripple current at the maximum input
voltage.
The corresponding inductor RMS current is:
2
23
12
RMS O O
I
II IA
⎛⎞
Δ
=+ =
⎝⎠
≈
I is the peak-to-peak ripple current which is fixed by
the inductor selection above. For a peak-to-peak current
of 30% of the full load current, the peak current at full
load will be 115% of the full load. The 1.5μH inductor
selected from the Sumida CDRH6D38 series has a 11m
DCR and a 4.0A DC current rating with a height of 4mm.
At full load, the inductor DC loss is 99mW for a 1% loss
in efficiency.
D1
B340LA
L1
1.5µH
C2
120µF
C1
10µF
VP
VCC
EN
GND
FB
LX
LX
VP
U1
AAT1154-3.3
R1
100
C3
0.1µF
C3 0.1µF 0603ZD104M AVX
L1 CDRH6D28-1.5µH Sumida
D1 B340LA Diodes Inc.
R2
100k
C1 Murata 10µF 6.3V X5R GRM42-6X5R106K6.3
C2 Murata 100µF 6. 3V GRM43-2 X5R 107M 100µF 6.3V (two or three in parallel
)
VIN 3.5V to 5.5V
VOUT 3.3V @ 3A
rtn
C4
100µF
C4 Vishay Sprague 100µF 16V 595D107X0016C 100µF 16V
C2 Vishay 120µF 6.3V 594D127X96R6R3C2T
Options
C2 TDK 100µF 6.3V C3325X5R0J107M 100µF 6.3V (two or three in parallel)
+
-
Figure 1: 3.3V, 3A Output.
11
AAT1154
1MHz 3A Step-Down DC/DC Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201993A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
Schottky Freewheeling Diode
The Schottky average current is the load current multi-
plied by one minus the duty cycle. For VIN at 5V and VOUT
at 3.3V, the average diode current is:
3.3
131 1
5.0
O
AVG O
IN
VV
II A A
VV
⎛⎞⎛⎞
=-= -
⎝⎠
⎝⎠
··=
With a 125°C maximum junction temperature and a
120°C/W thermal resistance, the maximum average
current is:
J(MAX) AMB 125 70 = 1.14
A
120 / 0.4
AVG
TT CC
IWV
-°- °
==
°C
θJA · VFWD ·
For overload, short-circuit, and excessive ambient tem-
perature conditions, the AAT1154 enters over-tempera-
ture shutdown mode, protecting the AAT1154 and the
output Schottky. In this mode, the output current is
limited internally until the junction temperature reaches
the temperature limit (see over-temperature character-
istics graphs). The diode reverse voltage must be rated
to withstand the input voltage.
Manufacturer Part Number Voltage Rating
Diodes Inc. B340LA 0.45V @ 3A
ROHM RB050L-40 0.45V @ 3A
Micro Semi 5820SM 0.46V @ 3A
Table 1: 3A Surface Mount Schottky Diodes.
Input Capacitor Selection
The primary function of the input capacitor is to provide
a low impedance loop for the edges of pulsed current
drawn by the AAT1154. A low ESR/ESL ceramic capacitor
is ideal for this function. To minimize stray inductance,
the capacitor should be placed as closely as possible to
the IC. This also keeps the high frequency content of the
input current localized, minimizing the radiated and con-
ducted EMI while facilitating optimum performance of
the AAT1154. Proper placement of the input capacitor C1
is shown in the layout in Figure 2. Ceramic X5R or X7R
capacitors are ideal. The size required will vary depend-
ing on the load, output voltage, and input voltage source
impedance characteristics. Typical values range from
1μF to 10μF. The input capacitor RMS current varies with
the input voltage and the output voltage. It is highest
when the input voltage is double the output voltage
where it is one half of the load current.
1
O
OO
RMS
IN IN
VV
II
VV
⎛⎞
= · · -
⎝⎠
A high ESR tantalum capacitor with a value about 10
times the input ceramic capacitor may also be required
when using a 10μF or smaller ceramic input bypass
capacitor. This dampens any input oscillations that may
occur due to the source inductance resonating with the
converter input impedance.
Output Capacitor
With no external compensation components, the output
capacitor has a strong effect on loop stability. Larger
output capacitance will reduce the crossover frequency
with greater phase margin. A 200μF ceramic capacitor
provides sufficient bulk capacitance to stabilize the out-
put during large load transitions and has ESR and ESL
characteristics necessary for very low output ripple. The
RMS ripple current is given by:
1
23
RMS
I(VOUT + VFWD) · (VIN - VOUT)
L · FS · VIN
=·
·
For a ceramic output capacitor, the dissipation due to the
RMS current and associated output ripple are negligible.
Tantalum capacitors with sufficiently low ESR to meet
output ripple requirements generally have an RMS cur-
rent rating much greater than that actually seen in this
application. The maximum tantalum output capacitor
ESR is:
RIPPLE
V
ESR ≤
ΔI
where I is the peak-to-peak inductor ripple current.
Due to the ESR zero associated with the tantalum capac-
itor, smaller values than those required with ceramic
capacitors provide more phase margin with a greater
loop crossover frequency.
12
AAT1154
1MHz 3A Step-Down DC/DC Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201993A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
Layout
Figures 2 and 3 display the suggested PCB layout for the
fixed output AAT1154. The following guidelines should be
used to help ensure a proper layout.
1. The connection from the input capacitor to the
Schottky anode should be as short as possible.
2. The input capacitor should connect as closely as pos-
sible to VP (Pins 5 and 8) and GND (Pin 2).
3. C1, L1, and CR1 should be connected as closely as
possible. The connection from the cathode of the
Schottky to the LX node should be as short as pos-
sible.
4. The feedback trace (Pin 1) should be separate from
any power trace and connect as closely as possible
to the load point. Sensing along a high-current load
trace can degrade DC load regulation.
5. The resistance of the trace from the load return to
GND (Pin 2) 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 reference
ground and the load return.
6. R1 and C3 are required in order to provide a cleaner
power source for the AAT1154 control circuitry.
Thermal
The losses associated with the AAT1154 output switching
MOSFET are due to switching losses and conduction
losses. The conduction losses are associated with the
RDS(ON) characteristics of the output switching device. At
the full load condition, assuming continuous conduction
mode (CCM), an accurate calculation of the RDS(ON) losses
can be derived from the following equations:
2
ON RMS DS(ON
)
PI R= ·
RDS(ON) losses
2
2
12
RMS O
I
II D
⎛⎞
Δ
=+·
⎝⎠
Internal switch RMS current
D is the duty cycle and VF is the forward drop of the
Schottky diode.
OF
IN F
VV
DVV
+
=+
I is the peak-to-peak inductor ripple current.
A simplified form of calculating the RDS(ON) and switching
losses is given by:
()
1
O
V
ΔI = D
LF
-
··
where IQ is the AAT1154 quiescent current.
Once the total losses have been determined, the junction
temperature can be derived. The thermal resistance
(JA) for the SOP-8 package mounted on an FR4 printed
circuit board in still air is 110°C/W.
TJ = P · JA + TAMB
TAMB is the maximum ambient temperature and TJ is the
resultant maximum junction temperature.
Figure 2: AAT1154 Fixed Output Figure 3: AAT1154 Fixed Output
Top Side Layout. Bottom Side Layout.
13
AAT1154
1MHz 3A Step-Down DC/DC Converter
DATA SHEET
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201993A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
Design Example
(See Figures 1 and 4 for reference)
IOUT 3A
IRIPPLE 30% of Full Load at Max VIN
VOUT 3.3V
VIN 5V 5%
FS 1MHz
TMAX 70°C
Inductor Selection
1
3.3 3.3
11.25μH
30.31 5
OUT OUT
VV
LIO · k · FSVIN
VV
AMHz V
⎛⎞
= · -
⎝⎠
⎛⎞
=·-=
⎝⎠
··
Use standard value of 1.5μH
Sumida Inductor Series CDRH6D38.
1
3.3 3.3V
1
1.5μ1 5.25V
OO
IN
VV
IL · FSV
V
HMHz
⎛⎞
Δ= -
=
⎝⎠
⎛⎞
-
⎝⎠
2
3A + 0.41A = 3.41A
PK OUT
I
II Δ
=+
=
·= 0.82
A
Efficiency vs. Load Current
(VIN = 5V; VOUT = 3.3V)
60
65
70
75
80
85
90
95
100
0.01 0.1 1 10
Output Current (A)
Efficiency (%)
Figure 4: 5V Input, 3.3V Output.
AAT1154 Junction Temperature
2
750 5
5V 2
0.539
ON IN
IN
PV
V
AV
Watts
⎛⎞
=+
+ IQ · =
⎝⎠
⎛ ⎞
++
=
=⎝ ⎠
70 110 / 0.54 129
J(MAX) AMB JA
TT P
CCWWC
=+
=°+° =
°
IO2 · RDS(ON) · VO
32 · 65mΩ · 3.3V
tSW · FS · IO
20ns · 1MHz · 3A μ·
·
·Θ
Diode
1
3.3
3 1 1.02
5
O
DIODE O
IN
V
II V
V
AA
V
⎛⎞
=· -
=
⎝⎠
⎛⎞
·- =
⎝⎠
0.35
F
VV=
0.35 1.01 0.354
W
PDIODE · VF · IDIODE
VA·=
Given an ambient thermal resistance of 120°C/W from
the manufacturer’s data sheet, TJ(MAX) of the diode is:
J(MAX)
70 120 / 0.354
112
AMB JA
TT P
CCW W
C
=+Θ
=°+ °
=°
·
·
Output Capacitor
The output capacitor value required for sufficient loop
phase margin depends on the type of capacitor selected.
For a low ESR ceramic capacitor, a minimum value of
200μF is required. For a low ESR tantalum capacitor,
lower values are acceptable. While the relatively higher
ESR associated with the tantalum capacitor will give
more phase margin and a more dampened transient
response, the output voltage ripple will be higher.
The 120μF Vishay 594D tantalum capacitor has an ESR
of 85m and a ripple current rating of 1.48Arms in a C
case size. Although smaller case sizes are sufficiently
rated for this ripple current, their ESR level would result
in excessive output ripple.
14
AAT1154
1MHz 3A Step-Down DC/DC Converter
DATA SHEET
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201993A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
The ESR requirement for a tantalum capacitor can be
estimated by:
100 121
0.82A
(VOUT + VF) · (VIN - VOUT)
L · FS · VIN
RIPPLE
VmV
ESR mΩ
I
≤ = =
Δ
1
23
1 3.65 1.7 240
1.5μ ·1 5
23
RMS
I
VV mArms
HMHzV
=·
=
·
·=
·
·
·
Two or three 1812 X5R 100uF 6.3V ceramic capacitors in
parallel also provide sufficient phase margin. The low
ESR and ESL associated with ceramic capacitors also
reduces output ripple significantly over that seen with
tantalum capacitors. Temperature rise due to ESR ripple
current dissipation is also reduced.
Input Capacitor
The input capacitor ripple is:
11.42
OO
RMS O
IN IN
VV
II Arms
VV
⎛⎞
=· · -=
⎝⎠
In the examples shown, C1 is a ceramic capacitor locat-
ed as closely to the IC as possible. C1 provides the low
impedance path for the sharp edges associated with the
input current. C4 may or may not be required, depend-
ing upon the impedance characteristics looking back into
the source. It serves to dampen out any input oscilla-
tions that may arise from a source that is highly induc-
tive. For most applications, where the source has suffi-
cient bulk capacitance and is fed directly to the AAT1154
through large PCB traces or planes, it is not required.
When operating the AAT1154 evaluation board on the
bench, C4 is required due to the inductance of the wires
running from the laboratory power supply to the evalua-
tion board.
Adjustable Output
For applications requiring an output other than the fixed
outputs available, the 1V version can be externally pro-
grammed. Resistors R3 and R4 of Figure 5 force the
output to regulate higher than 1V. For accurate results
(less than 1% error for all outputs), select R4 to be
10k. Once R4 has been selected, R3 can be calculated.
For a 1.25V output with R4 set to 10k, R3 is 2.5k.
R3 = (VO - 1) · R4 = 0.25 · 10k = 2.5k
Figures 6 and 7 display the suggested PCB layout for the
adjustable output AAT1154.
D1
B340LA
L1
1.5µH
C2
120µF
C1
10µF
VP
VCC
EN
GND
FB
LX
LX
VP
U1
AAT1154-1.0
R1
100
C3
0.1µF
C3 0.1µF 0603ZD104M AVX
L1 CDRH6D28-1.5µH Sumida
D1 B340LA Diodes Inc.
R2
100k
C1 Murata 10µF 6.3V X5R GRM42-6X5R106K6.3
C2 Murata 100µF 6. 3V GRM43-2 X5R 107M 100µF 6.3V (two or three in parallel
)
VIN 2.7V to 5.5V
VOUT 1.25V @3A
rtn
C4
100µF
C4 Vishay Sprague 100µF 16V 595D107X0016C 100µF 16V
R3
2.55k
R4
10.0k
C2 Vishay 120µF 6.3V 594D127X96R6R3C2T
Options
C2 TDK 100µF 6.3V C3325X5R0J107M 100µF 6.3V (two or three in parallel)
Figure 5: AAT1154 Evaluation Board With Adjustable Output.
15
AAT1154
1MHz 3A Step-Down DC/DC Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201993A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
Figure 6: Evaluation Board Adjustable Figure 7: Evaluation Board Adjustable
Output Top Side Layout. Output Bottom Side Layout.
Part Number Manufacturer Capacitance (μF) Voltage (V) Temp Co. Case
C4532X5ROJ107M TDK 100 6.3 X5R 1812
GRM43-2 X5R 107M 6.3 Murata 100 6.3 X5R 1812
GRM43-2 X5R 476K 6.3 Murata 47 6.3 X5R 1812
GRM42-6 X5R 106K 6.3 Murata 10 6.3 X5R 1206
594D127X_6R3C2T Vishay 120 6.3 C
595D107X0016C Vishay 100 16.0 C
Table 2: Capacitors.
Part Number Manufacturer Inductance (μH) I (Amps) DCR (Ω) Height (mm) Type
CDRH6D38-4763-T055 Sumida 1.5 4.0 0.014 4.0 Shielded
N05D B1R5M Taiyo Yuden 1.5 3.2 0.025 2.8 Non-Shielded
NP06DB B1R5M Taiyo Yuden 1.5 3.0 0.022 3.2 Shielded
LQH55DN1R5M03 Murata 1.5 3.7 0.022 4.7 Non-Shielded
LQH66SN1R5M03 Murata 1.5 3.8 0.016 4.7 Shielded
Table 3: Inductors.
Manufacturer Part Number VF
Diodes Inc. B340LA 0.45V @ 3A
ROHM RB050L-40 0.45V @ 3A
Micro Semi 5820SM 0.46V @ 3A
Table 4: Diodes.
16
AAT1154
1MHz 3A Step-Down DC/DC Converter
DATA SHEET
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201993A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
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Ordering Information
Output Voltage Package Marking Part Number (Tape and Reel)1
1.0V (Adj. VOUT 1.0V) SOP-8 115410 AAT1154IAS-1.0-T1
1.8V SOP-8 115418 AAT1154IAS-1.8-T1
2.5V SOP-8 115425 AAT1154IAS-2.5-T1
3.3V SOP-8 115433 AAT1154IAS-3.3-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
SOP-8
0.175 ±
±
0.075 6.00
±
0.20
3.90
±
0.10
1.55
±
0.20
1.27 BSC0.42
±
0.09
×
8
4.90
±
0.10
4
°
±
4
°
45
°
0.375
±
0.125
0.235
±
0.045
0.825
±
0.445
All dimensions in millimeters.
1. Sample stock is generally held on part numbers listed in BOLD.