201993A.pdf

DATA SHEET
AAT1154
1MHz 3A Step-Down DC/DC Converter
General Description
Features
The AAT1154 SwitchReg is a step-down switching converter 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 external parts count.
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The AAT1154 is available in a Pb-free SOP-8 package and
is rated over the -40°C to +85°C temperature range.
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
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Cable/DSL Modems
Computer Peripherals
High Efficiency Conversion from 5V or 3.3V Supply
Network Cards
Set-Top Boxes
Typical Application
INPUT
VP
10μF
100Ω
FB
AAT1154
VCC
1.5μH
LX
EN
0.1μF
GND
120μF
OUTPUT
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1
DATA SHEET
AAT1154
1MHz 3A Step-Down DC/DC Converter
Pin Descriptions
Pin #
Symbol
1
FB
2
GND
3
EN
4
5, 8
VCC
VP
6, 7
LX
Function
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.
Ground connection.
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 floating.
Power supply: supplies power for the internal circuitry.
Input supply voltage for converter power stage.
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
2
FB
1
8
VP
GND
2
7
LX
EN
3
6
LX
VCC
4
5
VP
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DATA SHEET
AAT1154
1MHz 3A Step-Down DC/DC Converter
Absolute Maximum Ratings1
TA = 25°C, unless otherwise noted.
Symbol
VCC, VP
VLX
VFB
VEN
TJ
VESD
Description
VCC, VP to GND
LX to GND
FB to GND
EN to GND
Operating Junction Temperature Range
ESD Rating2 - HBM
Value
Units
6
-0.3 to VP + 0.3
-0.3 to VCC + 0.3
-0.3 to VCC + 0.3
-40 to 150
3000
V
V
V
V
°C
V
Value
Units
110
909
°C/W
mW
Value
Units
-40 to +85
°C
Thermal Characteristics3
Symbol
JA
PD
Description
Thermal Resistance
Maximum Power Dissipation (TA = 25°C)4
Recommended Operating Conditions
Symbol
T
Description
Ambient Temperature Range
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.
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3
DATA SHEET
AAT1154
1MHz 3A Step-Down DC/DC Converter
Electrical Characteristics
VIN = VCC = VP = 5V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = 25°C.
Symbol
VIN
VOUT
Input Voltage Range
Output Voltage Tolerance
VUVLO
Under-Voltage Lockout
VUVLO(HYS)
IQ
ISHDN
ILIM
RDS(ON)H

VLOADREG
VLINEREG/
VIN
FOSC
VEN(L)
VEN(H)
TSD
THYS
4
Description
Conditions
VIN = VOUT + 0.2V to 5.5V, IOUT = 0A to 3A
VIN Rising
VIN Falling
Under-Voltage Lockout Hysteresis
Quiescent Supply Current
Shutdown Current
Current Limit
High Side Switch On Resistance
Efficiency
Load Regulation
No Load, VFB = 0V
VEN = 0V, VIN = 5.5V
TA = 25°C
TA = 25°C
IOUT = 1A
ILOAD = 0A to 3A
Line Regulation
VIN = 2.7V to 5.5V
Oscillator Frequency
Enable Threshold Low
Enable Threshold High
Over-Temperature Shutdown Threshold
Over-Temperature Shutdown Hysteresis
TA = 25°C
Min
Typ
Max
Units
5.5
5.0
2.5
V
%
2.7
-5.0
1.2
250
630
V
60
92
2.6
mV
μA
μA
A
m
%
%
0.75
%/V
1000
1.0
4.4
1
0.6
1.4
140
15
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MHz
V
V
°C
°C
DATA SHEET
AAT1154
1MHz 3A Step-Down DC/DC Converter
Typical Characteristics
RDS(ON) vs. Temperature
Efficiency vs. Load Current
(VIN = 5V; VOUT = 3.3V)
90
100
VIN = 2.7V
80
90
RDS(ON) (mΩ)
Efficiency (%)
95
85
80
75
70
VIN = 4.2V
VIN = 3.6V
70
60
VIN = 5.5V
50
VIN = 5V
65
40
60
0.01
0.1
1
-20
10
0
20
40
60
80
100
120
5
5.5
Temperature (°C)
Output Current (A)
RDS(ON) vs. VIN
Oscillator Frequency Variation vs.
Supply Voltage
(IDS = 1A)
70
0.5
RDS(ON) (mΩ
Ω)
Variation (%)
65
0.25
0
-0.25
60
55
50
45
40
-0.5
3.5
4
4.5
5
2.5
5.5
3
3.5
4
4.5
Input Voltage (V)
Input Voltage (V)
Oscillator Frequency Variation vs. Temperature
Enable Threshold vs. Input Voltage
(VIN = 5V)
1.2
Enable Threshold (V)
1
Variation (%)
0
-1
-2
-3
1.1
EN(H)
1
0.9
0.8
EN(L)
0.7
0.6
-4
-20
0
20
40
60
Temperature (°C)
80
100
2.5
3
3.5
4
4.5
5
5.5
Input Voltage (V)
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DATA SHEET
AAT1154
1MHz 3A Step-Down DC/DC Converter
Typical Characteristics
Line Regulation
Output Voltage vs. Temperature
(VOUT = 3.3V)
(IOUT = 2A)
0.4
Output Voltge Error (%)
1
Variation (%)
0.2
0
-0.2
-0.4
-0.6
-0.8
-20
0
20
40
60
80
IO = 0.3A
0
-1
-2
IO = 3.0A
-3
-4
-5
3
100
3.5
4
Over-Temperature Current vs. Input Voltage
-1.0
70°C
Output Error (%)
Output Current (A)
0.0
3.4
3
85°C
2.4
100°C
2.2
-2.0
-3.0
-4.0
-5.0
-6.0
-7.0
-8.0
-9.0
2
3.5
3.75
4
4.25
4.5
4.75
5
5.25
-10.0
5.5
0.01
0.1
Input Voltage (V)
10
Over-Temperature Shutdown
Current vs. Temperature
(FB = 0V)
(VOUT = 3.3V; VIN = 5.0V; L = 1.5μH)
0.8
VIN = 5.5V
6
VIN = 5.0V
Output Current (A)
Operating Current (mA)
1
Load Current (A)
Non-Switching Operating Current vs. Temperature
0.7
0.6
0.5
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
5.5
5
4.5
4
3.5
3
2.5
2
0.4
-20
0
20
40
60
Temperature (°C)
6
6
(VIN = 5.0V; VIN = 3.3V)
3.6
2.6
5.5
Load Regulation
(VOUT = 3.3V)
2.8
5
Input Voltage (V)
Temperature (°°C)
3.2
4.5
80
100
120
10
20
30
40
50
60
70
Temperature (°C)
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80
90
100
DATA SHEET
AAT1154
1MHz 3A Step-Down DC/DC Converter
Typical Characteristics
Inrush and Output Overshoot Characteristics
(3A Load)
Voltage (V)
(bottom traces)
14
4
12
10
2
8
0
6
-2
Input
4
-4
2
-6
Output
0
-8
-2
-10
0
0.4
0.8
1.2
1.6
6
Inductor Current
2
8
0
6
-2
Input
4
-4
2
-8
-2
2
-10
0
0.4
0.8
1.2
1.6
2
Time (ms)
Output Ripple
Output Ripple
(IOUT = 3.0A; VOUT = 3.3V; VIN = 5.0V)
(IOUT = 3.0A; VOUT = 3.3V; VIN = 5.0V)
4
7
6
2
6
0
5
0
5
-2
4
-2
4
-4
3
-4
3
-6
2
-6
2
-8
1
300µF 6.3VCeramic
TDK P/N C3325X5R0J107M
-10
0
-12
AC Output Ripple
(top) (mV)
7
2
-1
0
1
2
3
4
-8
5
0
5
-20
4
-40
3
-60
2
1
120μF 6.3V Tantalum Vishay
P/N 594D127X96R3C2T
-120
Time (μ
μs)
4
5
4
5
16
180
12
135
8
Gain (dB)
6
3
3
Phase
4
45
3x 100μF
0
-4
-8
90
2x 100μF
100μF 6.3V Ceramic
TDK P/N C3225X5R0J107M
0
-12
-1
-16
10000
Frequency (Hz)
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0
-45
-90
Phase (degrees)
20
Inductor Current
(bottom) (A)
7
2
2
Loop Crossover Gain and Phase
40
1
1
Time (μ
μs)
Tantalum Output Ripple
0
-1
0
(IOUT = 3.0A; VOUT = 3.3V; VIN = 5.0V)
-100
0
-12
Time (μ
μs)
-80
1
200μF 6.3V Ceramic
TDK P/N C3325X5R0J107M
-10
Inductor Current
(bottom) (A)
4
Inductor Current
(bottom) (A)
AC Output Ripple
top (mV)
-6
Output
0
Time (ms)
AC Output Ripple (top)
(mV)
4
10
Inductor Current (A)
(top trace)
6
Inductor Current (A)
(top trace)
Inductor Current
12
(No Load)
Voltage (V)
(bottom traces)
14
Inrush and Output Overshoot Characteristics
-135
-180
100000
7
DATA SHEET
AAT1154
1MHz 3A Step-Down DC/DC Converter
Typical Characteristics
Loop Crossover Gain and Phase
180
120μF 6.3V Tantalum
Vishay P/N 594D127X96R3C2T
12
Gain (dB)
Phase
45
0
0
-4
-45
Gain
5
-200
4
-300
3
-400
2
-500
1
0
-90
-12
-135
-600
-180
100000
-700
Frequency (Hz)
Output Voltage
(top) (mV)
5
-200
4
-300
3
-400
2
-500
1
3
-400
2
-500
1
-700
400
0
-600
-1
-700
500
0
120μF 6.3V Tantalum
Vishay P/N 594D127X96R3C2T
0
100
200
300
-1
400
Time (μ
μs)
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500
Inductor Current
(bottom) (A)
6
-100
Inductor Current
(bottom) (A)
7
0
4
-600
8
100
-300
μs)
Time (μ
500
6
-200
300
400
7
5
200
300
Tantalum Transient Response
-100
100
200
(IOUT = 0 to 3.0A; VOUT = 3.3V; VIN = 5.0V)
Output Voltage
(top) (mV)
2x 100μF 6.3V Ceramic
TDK P/N C3325X5R0J107M
0
100
μs)
Time (μ
Transient Response
0
-1
0
(IOUT = 0 to 3.0A; VOUT = 3.3V; VIN = 5.0V)
100
6
-100
-8
-16
10000
7
3x 100μF 6.3V Ceramic
TDK P/N C3325X5R0J107M
0
Inductor Current
(bottom) (A)
90
Phase (degrees)
8
4
100
135
Output Voltage
(top) (mV)
16
Transient Response
(IOUT = 0 to 3.0A; VOUT = 3.3V; VIN = 5.0V)
DATA SHEET
AAT1154
1MHz 3A Step-Down DC/DC Converter
Functional Block Diagram
VCC
VP = 2.7V to 5.5V
REF
FB
OP. AMP
CMP
DH
LOGIC
OSC
LX
Temp.
Sensing
GND
EN
Applications Information
lation. The crossover frequency and phase margin are
set by the output capacitor value.
Main Control Loop
Duty cycle extends to 100% as the input voltage
approaches the output voltage. Thermal shutdown protection disables the device in the event of a short-circuit
or overload condition.
The AAT1154 is a peak current mode step-down converter. 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 constant 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-
Soft Start/Enable
Soft start controls the current limit when the input voltage 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 isolate the internal control circuitry from switching noise. In
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9
DATA SHEET
AAT1154
1MHz 3A Step-Down DC/DC Converter
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:
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
L =I
Over-temperature and current limit circuitry protects the
AAT1154 and the external Schottky diode during overload, 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.
OUT
=
VOUT
VOUT ⎞
⎛
· k · FS · ⎝1 - VIN(MAX)⎠
3.3V
⎞
⎛
⎞
⎛
· 1 - 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.
Inductor
The corresponding inductor RMS current is:
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.
IRMS =
⎛ 2 ΔI 2 ⎞
I +
≈ I O = 3A
⎝ O
12 ⎠
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.
VIN 3.5V to 5.5V
VOUT 3.3V @ 3A
R1
100
C4
100µF
R2
100k
U1
AAT1154-3.3
FB
VP
L1
1.5µH
GND LX
EN
C1
10µF
C3
0.1µF
rtn
LX
VCC VP
D1
B340LA
C2
120µF
+
-
C1 Murata 10µF 6.3V X5R GRM42-6X5R106K6.3
C2 Vishay120µF 6.3V 594D127X96R6R3C2T
C3 0.1µF 0603ZD104M AVX
C4 Vishay Sprague 100µF 16V 595D107X0016C 100µF 16V
D1 B340LA Diodes Inc.
L1 CDRH6D28-1.5µH Sumida
Options
C2 Murata 100µF 6. 3V GRM43-2 X5R 107M 100µF 6.3V (two or three in parallel)
C2 TDK 100µF 6.3V C3325X5R0J107M 100µF 6.3V (two or three in parallel)
Figure 1: 3.3V, 3A Output.
10
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DATA SHEET
AAT1154
1MHz 3A Step-Down DC/DC Converter
Schottky Freewheeling Diode
The Schottky average current is the load current multiplied by one minus the duty cycle. For VIN at 5V and VOUT
at 3.3V, the average diode current is:
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.
IRMS = IO ·
V
3.3V ⎞
= 1A
I AVG = IO · ⎛1 - O ⎞ = 3A · ⎛1 ⎝ VIN ⎠
⎝ 5.0V ⎠
With a 125°C maximum junction temperature and a
120°C/W thermal resistance, the maximum average
current is:
IAVG =
TJ(MAX)- TAMB
θJA · VFWD
=
125°C - 70°C
= 1.14A
120 °C/ W · 0.4V
For overload, short-circuit, and excessive ambient temperature conditions, the AAT1154 enters over-temperature 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 characteristics graphs). The diode reverse voltage must be rated
to withstand the input voltage.
Manufacturer
Part Number
Voltage Rating
Diodes Inc.
ROHM
Micro Semi
B340LA
RB050L-40
5820SM
0.45V @ 3A
0.45V @ 3A
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 conducted 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 depending on the load, output voltage, and input voltage source
impedance characteristics. Typical values range from
VO ⎛
V
· 1- O ⎞
VIN ⎝ VIN ⎠
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 output during large load transitions and has ESR and ESL
characteristics necessary for very low output ripple. The
RMS ripple current is given by:
IRMS =
1
(VOUT + VFWD) · (VIN - VOUT)
L · FS · VIN
2· 3
·
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 current rating much greater than that actually seen in this
application. The maximum tantalum output capacitor
ESR is:
ESR ≤
VRIPPLE
ΔI
where I is the peak-to-peak inductor ripple current.
Due to the ESR zero associated with the tantalum capacitor, smaller values than those required with ceramic
capacitors provide more phase margin with a greater
loop crossover frequency.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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11
DATA SHEET
AAT1154
1MHz 3A Step-Down DC/DC Converter
Figure 2: AAT1154 Fixed Output
Top Side Layout.
Figure 3: AAT1154 Fixed Output
Bottom Side Layout.
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.
2.
3.
4.
5.
6.
The connection from the input capacitor to the
Schottky anode should be as short as possible.
The input capacitor should connect as closely as possible to VP (Pins 5 and 8) and GND (Pin 2).
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 possible.
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.
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.
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:
12
PON = I RMS2 · RDS(ON)
RDS(ON) losses
IRMS =
2
⎛ 2 ΔI ⎞
·D
IO +
⎝
12 ⎠
Internal switch RMS current
D is the duty cycle and VF is the forward drop of the
Schottky diode.
D=
VO + VF
VIN + VF
I is the peak-to-peak inductor ripple current.
A simplified form of calculating the RDS(ON) and switching
losses is given by:
ΔI =
VO
· (1 - D )
L·F
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.
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DATA SHEET
AAT1154
1MHz 3A Step-Down DC/DC Converter
Design Example
AAT1154 Junction Temperature
(See Figures 1 and 4 for reference)
IOUT
IRIPPLE
VOUT
VIN
FS
TMAX
PON =
3A
30% of Full Load at Max VIN
3.3V
5V 5%
1MHz
70°C
=
=
TJ(MAX)= TAMB + ΘJA · P
= 70°C + 110°C / W · 0.54W = 129°C
VOUT
V
· ⎛1 - OUT ⎞
VIN ⎠
IO · k · FS ⎝
Diode
3.3V
⎛ 3.3 V ⎞
· 1= 1.25μH
3A · 0.3 ·1MHz ⎝
5V ⎠
⎛ V ⎞
IDIODE= IO · 1 - O
⎝ VIN ⎠
Use standard value of 1.5μH
⎛ 3.3V ⎞
= 3A · 1 = 1.02A
⎝
5V ⎠
Sumida Inductor Series CDRH6D38.
VF = 0.35 V
VO ⎛
V ⎞
ΔI =
1- O
L · FS ⎝ VIN ⎠
=
PDIODE · VF · IDIODE
0.35V · 1.01A = 0.354W
3.3V
3.3V ⎞
⎛
1= 0.82A
⎝
1.5μH · 1MHz
5.25V⎠
I PK = IOUT +
⎞
32 · 65mΩ · 3.3V ⎛ 20ns · 1MHz · 3A
+
+ 750μA · 5V
⎝
⎠
5V
2
= 0.539 Watts
Inductor Selection
L=
IO2 · RDS(ON) · VO ⎛ tSW · FS · IO
+ IQ⎞ · VIN =
+
VIN
2
⎝
⎠
Given an ambient thermal resistance of 120°C/W from
the manufacturer’s data sheet, TJ(MAX) of the diode is:
ΔI
2
= 3A + 0.41A = 3.41A
TJ(MAX) = TAMB + ΘJA · P
= 70°C + 120°C / W · 0.354W
= 112°C
Efficiency vs. Load Current
(VIN = 5V; VOUT = 3.3V)
100
Output Capacitor
Efficiency (%)
95
90
85
80
75
70
65
60
0.01
0.1
1
Output Current (A)
Figure 4: 5V Input, 3.3V Output.
10
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.
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13
DATA SHEET
AAT1154
1MHz 3A Step-Down DC/DC Converter
The ESR requirement for a tantalum capacitor can be
estimated by:
ESR ≤
IRMS =
=
impedance path for the sharp edges associated with the
input current. C4 may or may not be required, depending upon the impedance characteristics looking back into
the source. It serves to dampen out any input oscillations that may arise from a source that is highly inductive. For most applications, where the source has sufficient 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 evaluation board.
VRIPPLE 100 mV
=
= 121 mΩ
ΔI
0.82A
1
2· 3
·
(VOUT + VF) · (VIN - VOUT)
L · FS · VIN
3.65V ·1.7 V
= 240mArms
2 · 3 1.5μH · 1MHz · 5V
1
·
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.
Adjustable Output
For applications requiring an output other than the fixed
outputs available, the 1V version can be externally programmed. 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.
Input Capacitor
The input capacitor ripple is:
IRMS = I O ·
R3 = (VO - 1) · R4 = 0.25 · 10k = 2.5k
VO ⎛
V ⎞
· 1 - O = 1.42 Arms
⎝
VIN
VIN ⎠
Figures 6 and 7 display the suggested PCB layout for the
adjustable output AAT1154.
In the examples shown, C1 is a ceramic capacitor located as closely to the IC as possible. C1 provides the low
VIN 2.7V to 5.5V
VOUT 1.25V @3A
R1
100
C4
100µF
R2
100k
R3
2.55k
U1
AAT1154-1.0
FB
VP
L1
1.5µH
GND LX
EN
C1
10µF
C3
0.1µF
rtn
LX
VCC VP
R4
10.0k
D1
B340LA
C2
120µF
C1 Murata 10µF 6.3V X5R GRM42-6X5R106K6.3
C2 Vishay 120µF 6.3V 594D127X96R6R3C2T
C3 0.1µF 0603ZD104M AVX
C4 Vishay Sprague 100µF 16V 595D107X0016C 100µF 16V
D1 B340LA Diodes Inc.
L1 CDRH6D28-1.5µH Sumida
Options
C2 Murata 100µF 6. 3V GRM43-2 X5R 107M 100µF 6.3V (two or three in parallel)
C2 TDK 100µF 6.3V C3325X5R0J107M 100µF 6.3V (two or three in parallel)
Figure 5: AAT1154 Evaluation Board With Adjustable Output.
14
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
DATA SHEET
AAT1154
1MHz 3A Step-Down DC/DC Converter
Figure 6: Evaluation Board Adjustable
Output Top Side Layout.
Figure 7: Evaluation Board Adjustable
Output Bottom Side Layout.
Part Number
Manufacturer
Capacitance (μF)
Voltage (V)
Temp Co.
Case
C4532X5ROJ107M
GRM43-2 X5R 107M 6.3
GRM43-2 X5R 476K 6.3
GRM42-6 X5R 106K 6.3
594D127X_6R3C2T
595D107X0016C
TDK
Murata
Murata
Murata
Vishay
Vishay
100
100
47
10
120
100
6.3
6.3
6.3
6.3
6.3
16.0
X5R
X5R
X5R
X5R
1812
1812
1812
1206
C
C
Table 2: Capacitors.
Part Number
Manufacturer
Inductance (μH)
I (Amps)
DCR (Ω)
Height (mm)
Type
CDRH6D38-4763-T055
N05D B1R5M
NP06DB B1R5M
LQH55DN1R5M03
LQH66SN1R5M03
Sumida
Taiyo Yuden
Taiyo Yuden
Murata
Murata
1.5
1.5
1.5
1.5
1.5
4.0
3.2
3.0
3.7
3.8
0.014
0.025
0.022
0.022
0.016
4.0
2.8
3.2
4.7
4.7
Shielded
Non-Shielded
Shielded
Non-Shielded
Shielded
Table 3: Inductors.
Manufacturer
Part Number
VF
Diodes Inc.
ROHM
Micro Semi
B340LA
RB050L-40
5820SM
0.45V @ 3A
0.45V @ 3A
0.46V @ 3A
Table 4: Diodes.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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15
DATA SHEET
AAT1154
1MHz 3A Step-Down DC/DC Converter
Ordering Information
Output Voltage
Package
Marking
Part Number (Tape and Reel)1
1.0V (Adj. VOUT  1.0V)
1.8V
2.5V
3.3V
SOP-8
SOP-8
SOP-8
SOP-8
115410
115418
115425
115433
AAT1154IAS-1.0-T1
AAT1154IAS-1.8-T1
AAT1154IAS-2.5-T1
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
6.00 ± 0.20
3.90 ± 0.10
SOP-8
4.90 ± 0.10
0.42 ± 0.09 × 8
1.27 BSC
45°
4° ± 4°
0.175 ± 0.075
1.55 ± 0.20
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.
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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