Skyworks AAT2146W Low-noise, fast transient 600ma step-down converter Datasheet

DATA SHEET
AAT2146W
Low-Noise, Fast Transient 600mA Step-Down Converter
General Description
Features
The AAT2146W SwitchReg is a 2MHz fixed frequency
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 AAT2146W is
ideal for applications where fixed frequency and low ripple voltage are required over the full range of load conditions.
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The AAT2146W is programmable with external feedback
resistors. It can deliver 600mA of load current while
maintaining a low 150μA no-load quiescent current. The
2MHz switching frequency minimizes the size of external
components while keeping switching losses low.
The AAT2146W is designed to maintain high efficiency
throughout the operating range, which is critical for portable applications.
The AAT2146W is available in the Pb-free, space-saving
2.0x2.2mm SC70JW-8 package and is rated over the
-40°C to +85°C temperature range.
VIN Range: 2.7V to 5.5V
Low Ripple Voltage Fixed Frequency PWM Mode
VOUT Adjustable from 0.6V to VIN
Efficiency up to 96%
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
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Cellular Phones
Digital Cameras
Handheld Instruments
Microprocessor / DSP Core / IO Power
PDAs and Handheld Computers
USB Devices
Typical Application
U1
AAT2146W
VIN
C2
2.2µF
VIN
LX
EN
OUT
AGND
PGND
PGND
PGND
L1
4.7µH
VO
C1
4.7µF
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202008A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
1
DATA SHEET
AAT2146W
Low-Noise, Fast Transient 600mA Step-Down Converter
Pin Descriptions
Pin #
Symbol
1
EN
2
OUT
3
VIN
4
LX
5
6, 7, 8
AGND
PGND
Function
Enable pin.
Feedback input pin. This pin is connected either directly to the converter output or to an external
resistive divider for an adjustable output.
Input supply voltage for the converter.
Switching node. Connect the inductor to this pin. It is internally connected to the drain of both
high- and low-side MOSFETs.
Non-power signal ground pin.
Main power ground return pins. Connect to the output and input capacitor return.
Pin Configuration
SC70JW-8
(Top View)
2
EN
1
8
PGND
OUT
2
7
PGND
VIN
3
6
PGND
LX
4
5
AGND
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202008A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
DATA SHEET
AAT2146W
Low-Noise, Fast Transient 600mA Step-Down Converter
Absolute Maximum Ratings1
Symbol
VIN
VLX
VOUT
VEN
TJ
TLEAD
TA
Description
Input Voltage GND
LX to GND
OUT to GND
EN to GND
Junction Temperature Range
Maximum Soldering Temperature (at leads, 10 sec.)
Operating Temperature Range
Value
Units
-0.3 to 6.0
-0.3 to VIN + 0.3
-0.3 to VIN + 0.3
-0.3 to VIN + 0.3
-40 to 150
300
-40 to 85
V
V
V
V
°C
°C
°C
Value
Units
625
160
mW
°C/W
Thermal Information
Symbol
PD
JA
Description
Maximum Power Dissipation2, 3
Thermal Resistance2
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.
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 • [email protected] • www.skyworksinc.com
202008A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
3
DATA SHEET
AAT2146W
Low-Noise, Fast Transient 600mA Step-Down Converter
Electrical Characteristics1
TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C, VIN = 3.6V.
Symbol
Description
Conditions
Step-Down Converter
VIN
Input Voltage
VUVLO
VOUT
VOUT
VOUT
IQ
ISHDN
ILIM
RDS(ON)H
RDS(ON)L
VLinereg
IOUT
TS
FOSC
TSD
THYS
EN
VEN(L)
VEN(H)
IEN
UVLO Threshold
Out Voltage Accuracy
Output Voltage Tolerance
Output Voltage Range
Quiescent Current
Shutdown Current
P-Channel Current Limit
High Side Switch On Resistance
Low Side Switch On Resistance
Line Regulation
Out Leakage Current
Start-Up Time
Oscillator Frequency
Over-Temperature Shutdown Threshold
Over-Temperature Shutdown Hysteresis
Enable Threshold Low
Enable Threshold High
Input Low Current
Min
Typ
2.7
VIN Rising
Hysteresis
VIN Falling
No Load; TA = 25°C
IOUT = 0mA to 600mA, VIN = 2.7V to 5.5V
Max
Units
5.5
2.7
V
V
mV
V
mV
+3.0
VIN
300
1.0
%
V
μA
μA
mA


%/V
μA
μs
MHz
°C
°C
100
1.8
600
-3.0
0.6
No Load, Not Switching
EN = AGND = PGND
150
800
0.35
0.30
0.1
VIN = 2.7V to 5.5V; IOUT = 600mA
0.6V Output
From Enable to Output Regulation
TA = 25°C
0.2
150
2.0
140
15
0.6
VIN = VOUT = 5.5V
1.4
-1.0
1.0
V
V
μA
1. The AAT2146W is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and correlation with statistical process controls.
4
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202008A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
DATA SHEET
AAT2146W
Low-Noise, Fast Transient 600mA Step-Down Converter
Typical Characteristics1
Efficiency vs. Output Current
Load Regulation
(VOUT= 1.8V)
100
Vin=5.5V
90
Vin=4.2V
70
Vin=3.6V
60
Vin=3.0V
Vin=2.7V
50
40
30
20
10
0
0.1
Vin=5.5V
0.8
Vin=5.0V
80
Load Regulation (%)
Efficiency (%)
(VOUT= 1.8V)
1.0
1
10
100
Vin=4.2V
0.4
Vin=3.6V
Vin=3.0V
0.2
Vin=2.7V
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
0.1
1000
Vin=5.0V
0.6
1
Output Current (mA)
Vin=5.0V
Vin=4.2V
70
Vin=3.6V
Load Regulation (%)
Efficiency (%)
(VOUT= 2.5V)
1.0
Vin=5.5V
80
Vin=3.0V
60
50
40
30
20
10
Vin=5.5V
0.8
Vin=5.0V
0.6
Vin=4.2V
Vin=3.6V
0.4
Vin=3.0V
0.2
0.0
-0.2
-0.4
-0.6
-0.8
0
0.1
1
10
100
-1.0
0.1
1000
Output Current (mA)
1
80
Vin=5.5V
Vin=4.2V
60
50
40
30
20
Vin=5.0V
0.6
Vin=4.2V
0.4
0.2
0.0
-0.2
-0.4
-0.6
-0.8
10
0.1
Vin=5.5V
0.8
Vin=5.0V
70
0
1000
(VOUT= 3.3V)
1.0
Load Regulation (%)
90
100
Load Regulation
(VOUT= 3.3V)
100
10
Output Current (mA)
`
Efficiency vs. Output Current
Efficiency (%)
1000
Load Regulation
(VOUT= 2.5V)
90
100
Output Current (mA)
Efficiency vs. Output Current
100
10
1
10
100
Output Current (mA)
1000
-1.0
0.1
1
10
100
1000
Output Current (mA)
1. See figure 2 for the application test circuit.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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5
DATA SHEET
AAT2146W
Low-Noise, Fast Transient 600mA Step-Down Converter
Typical Characteristics
Oscillator Frequency Variation vs. Input Voltage
(VOUT= 1.8V)
0.5
Iout=600mA
Line Regulation (%)
0.4
Iout=400mA
0.3
Iout=1mA
0.2
0.1
0.0
-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
Oscillator Frequency Variation (%)
Line Regulation
(VOUT= 1.8V; IOUT= 600mA)
4
3
2
1
0
-1
-2
-3
-4
2.7
3.1
3.5
Output Voltage Error vs. Temperature
Quiescent Current (mA)
Output Voltage Error (%)
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
35
60
85
3
2.5
2
T=85C
T=25C
1.5
2.7
Load Transient
3.5
3.9
4.3
4.7
5.1
5.5
1.85
0.9
1.80
0.8
1.75
0.7
1.70
0.6
1.65
0.5
1.60
0.4
1.55
0.3
1.50
0.2
Output Voltage
(100mV/div) (top)
1.0
Load Transient
(VOUT= 1.8V; VIN= 3.6V; IOUT= 300mA to 400mA; CFF= 100pF)
1.90
1.0
1.85
0.9
1.80
0.8
1.75
0.7
1.70
0.6
1.65
0.5
1.60
0.4
1.55
0.3
1.50
0.2
Time (100μs/div)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202008A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
Output Current
(100mA/div) (bottom)
1.90
Output Current
(100mA/div) (bottom)
Output Voltage
(100mV/div) (top)
T=-40C
3.1
Input Voltage (V)
(VOUT= 1.8V; VIN= 3.6V; IOUT= 300mA to 400mA; CFF= 0pF)
6
5.5
3.5
Temperature (°C)
Time (100µs/div)
5.1
4
2.0
10
4.7
Quiescent Current vs. Input Voltage
(VOUT= 1.8V; VIN= 3.6V; IOUT= 400mA)
-15
4.3
Input Voltage (V)
Input Voltage (V)
-2.0
-40
3.9
PRODUCT
DATASHEET
DATA
SHEET
AAT2146W
AAT2146W
SwitchRegTM
Low Noise, Fast
FastTransient
Transient 600mA
600mA Step-Down
Step-Down Converter
Converter
Low-Noise,
Typical Characteristics
Line Transient
(VOUT= 1.8V; VIN= 3.6 to 4.2V; IOUT= 400mA; CFF = 0pF)
4.8
1.92
1.2
4.2
1.90
1.8
1.0
3.6
1.88
1.7
0.8
3.0
1.86
1.6
0.6
2.4
1.84
1.5
0.4
1.8
1.82
1.4
0.2
1.2
1.80
1.3
0.0
0.6
1.78
1.2
-0.2
0.0
1.76
Input Voltage
(500mV/div) (top)
1.4
1.9
Time (100µs/div)
Time (50µs/div)
P-Channel RDS(ON) vs. Input Voltage
N-Channel RDS(ON) vs. Input Voltage
(Junction Temperature)
(Junction Temperature)
550
450
120°C
100°C
85°C
25°C
500
RDS(ON) (mΩ
Ω)
RDS(ON) (mΩ
Ω)
550
120°C
100°C
85°C
25°C
500
400
350
300
250
200
2.5
450
400
350
300
250
3
3.5
4
4.5
5
5.5
6
200
2.5
Input Voltage (V)
3
3.5
4
4.5
5
Soft Start
(VOUT= 1.8V; VIN= 3.6V; IOUT= 400mA)
6
0.9
1.81
0.8
1.80
0.7
1.79
0.6
1.78
0.5
1.77
0.4
1.76
0.3
1.75
0.2
1.74
0.1
4
3.5
3
3.0
2
2.5
1
2.0
0
1.5
-1
1.0
-2
0.5
-3
0.0
-4
-0.5
Inductor Current
(500mA/div) (bottom)
1.82
Enable Voltage (2V/div) (top)
Output Voltage (2V/div) (middle)
Output Voltage Ripple
(VOUT= 1.8V; VIN= 3.6V; IOUT= 400mA)
Time (500ns/div)
5.5
Input Voltage (V)
Inductor Current
(100mA/div) (bottom)
Output Voltage
(10mV/div) (top)
Output Voltage
(50mV/div) (bottom)
2.0
Output Current
(200mA/div) (bottom)
Output Voltage
(100mV/div) (top)
Load Transient
(VOUT= 1.8V; VIN= 3.6V; IOUT= 1mA to 300mA; CFF= 100pF)
Time (100µs/div)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202008A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
7
DATA SHEET
AAT2146W
Low-Noise, Fast Transient 600mA Step-Down Converter
Functional Block Diagram
OUT
VIN
Err
Amp
.
DH
Voltage
Reference
EN
INPUT
LX
Logic
DL
PGND
AGND
Functional Description
The AAT2146W is a high performance, fixed frequency,
600mA, 2MHz, monolithic step-down converter. It has
been designed with the goal of minimizing external components, size and optimizing efficiency over the complete load range, and produces reduced ripple voltage
and spectral noise. Typically, a 4.7μH inductor and a
4.7μF ceramic output capacitor are recommended (see
tables 4 and 5).
The adjustable output can be programmed with external
feedback to any voltage, ranging from 0.6V to the input
voltage. An additional feed-forward capacitor (CFF) can
also be added to the external feedback to provide
improved transient response (see Figure 1).
8
At dropout, the converter duty cycle increases to 100%
and the output voltage tracks the input voltage minus
the RDS(ON) voltage 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.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202008A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
DATA SHEET
AAT2146W
Low-Noise, Fast Transient 600mA Step-Down Converter
1
2
3
VIN
Enable
U1
AAT2146W
CFF
VOUT
C1
10µF
1
R1
2
118k
3
L1
4.7µH
4
EN
PGND
OUT
PGND
VIN
PGND
LX
AGND
8
7
6
5
C2
4.7µF
R2
59k
GND
LX
U1 AAT2146W SC70JW-8
L1 CDRH3D16-4R7
C1 10µF 10V 0805 X5R
C2 4.7µF 10V 0805 X5R
CFF 100pF 0402 X5R
Figure 1: Enhanced Transient Response Schematic.
Control Loop
The AAT2146W is a peak current mode step-down converter. 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 compensation signal is added to the sensed current to maintain
stability for duty cycles greater than 50%. The peak current mode loop appears as a voltage-programmed current 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 regulate a constant output voltage for all load and line
conditions. Internal loop compensation terminates the
transconductance voltage error amplifier output. The
error amplifier reference is fixed at 0.6V.
Soft Start / Enable
Current Limit and
Over-Temperature Protection
For overload conditions, the peak input current is limited
cycle by cycle.
Thermal protection completely disables switching when
junction temperature becomes excessive. The junction
over-temperature threshold is 140°C with 15°C of hysteresis. Once an over-temperature or over-current fault
condition 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.
Soft start limits the current surge seen at the input and
eliminates output voltage overshoot. When pulled low,
the enable input forces the AAT2146W into a low-power,
non-switching state. The total input current during shutdown is less than 1μA.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202008A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
9
DATA SHEET
AAT2146W
Low-Noise, Fast Transient 600mA Step-Down Converter
Applications Information
Inductor Selection
The step-down converter uses peak current mode control 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 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.
m=
The 4.7μH CDRH3D16 series inductor selected from
Sumida has a 105m DCR and a 900mA DC current rating. At full load, the inductor DC loss is 17mW which
gives a 2.8% loss in efficiency for a 400mA, 1.5V output.
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 voltage ripple level (VPP)
and solve for CIN. The calculated value varies with input
voltage and is a maximum when VIN is double the output
voltage.
0.75 ⋅ VO 0.75 ⋅ 1.5V
A
=
= 0.24
L
4.7µH
µs
This is the internal slope compensation. When externally
programming to 2.5V, the calculated inductance is
7.5μH.
0.75 ⋅ VO
µs
0.75 ⋅ VO
≈ 3 A ⋅ VO
L=
=
m
A
0.24A µs
V
VO
· 1- O
VIN
VIN
CIN =
VPP
- ESR · fsw
IO
For VIN = 2 . VO
V
VO
· 1- O
VIN
VIN
Table 1 displays inductor values for the AAT2146W.
Output Voltage
Inductor
1V, 1.2V
1.5V, 1.8V
2.5V, 3.3V
2.2μH
4.7μH
6.8μH
VPP
- ESR · 4 · fsw
IO
Always examine the ceramic capacitor DC voltage coefficient 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.
The maximum input capacitor RMS current is:
IRMS = IO ·
Table 1: Inductor Values.
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 saturation 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.
10
1
4
1
CIN(MIN) =
µs
= 3 ⋅ 2.5V = 7.5µH
A
In this case, a standard 6.8μH value is selected.
=
VO ⎛
V ⎞
· 1- O
VIN ⎝
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.
VO ⎛
V ⎞
· 1- O =
VIN ⎝
VIN ⎠
D · (1 - D) =
0.52 =
For VIN = 2 · VO
IRMS(MAX) =
IO
2
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202008A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
1
2
DATA SHEET
AAT2146W
Low-Noise, Fast Transient 600mA Step-Down Converter
VO
⎛
V ⎞
· 1- O
The term V ⎝ V ⎠ appears in both the input voltage ripple 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.
IN
IN
The input capacitor provides a low impedance loop for
the edges of pulsed current drawn by the AAT2146W.
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 evaluation 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 during 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 inductance cannot be reduced to a level that does not affect
the converter performance, a high ESR tantalum or aluminum 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 voltage and
provides 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 characteristics necessary for low output voltage 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 relationship of the output voltage droop during the three
switching cycles to the output capacitance can be estimated by:
COUT =
3 · ΔILOAD
VDROOP · fsw
Once the average inductor current increases to the DC
load level, the output voltage recovers. The above equation 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 capacitance will reduce the crossover frequency with greater
phase margin.
The maximum output capacitor RMS ripple current is
given by:
IRMS(MAX) =
1
VOUT · (VIN(MAX) - VOUT)
L · fsw · VIN(MAX)
2· 3
·
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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11
DATA SHEET
AAT2146W
Low-Noise, Fast Transient 600mA Step-Down Converter
Figure 2: AAT2146W Evaluation Board
Component Side Layout.
Figure 3: Exploded View of AAT2146W
Evaluation Board Component Side Layout.
Figure 4: AAT2146W Evaluation Board
Solder Side Layout.
Adjustable Output Resistor Selection
Feedback 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 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 voltages with R2 set to either 59k for good noise
immunity or 221k for reduced no load input current.
12
⎛ VOUT ⎞
⎛ 1.5V ⎞
R1 = V
-1 · R2 = 0.6V - 1 · 59kΩ = 88.5kΩ
⎝ REF ⎠
⎝
⎠
The AAT2146W combined with an external feedforward
capacitor (C4 in Figure 5), delivers enhanced transient
response for extreme pulsed load applications.
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DATA SHEET
AAT2146W
Low-Noise, Fast Transient 600mA Step-Down Converter
R2 = 59k
R2 = 221k
VOUT (V)
R1 (k)
R1 (k)
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.8
1.85
2.0
2.5
3.3
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
267
75
113
150
187
221
261
301
332
442
464
523
715
1000
switching devices. A simplified form of the losses is given
by:
PTOTAL =
IO2 · (RDS(ON)HS · VO + RDS(ON)LS · [VIN - VO])
VIN
+ (tsw · fsw · IO + IQ) · VIN
IQ is the step-down converter quiescent current. The
term tsw is used to estimate the full load step-down converter switching losses.
For the condition where the step-down converter is in
dropout at 100% duty cycle, the total device dissipation
reduces to:
PTOTAL = IO2 · RDS(ON)HS + IQ · VIN
Table 2: Adjustable Resistor Values For Use With
0.6V Step-Down Converter.
Since RDS(ON), quiescent current, and switching losses all
vary with input voltage, the total losses should be investigated over the complete input voltage range.
Thermal Calculations
Given the total losses, the maximum junction temperature can be derived from the JA for the SC70JW-8 package which is 160°C/W.
There are three types of losses associated with the
AAT2146W step-down converter: switching losses, conduction 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
TJ(MAX) = PTOTAL · QJA + TA
1
2
3
Enable
VIN
C4
100pF
U1
AAT2146W
1
VOUT =1.8V
R1
2
L1 118k
4.7µH
C1
10µF
C3
n/a
3
4
R2
59k
EN
PGND
OUT
PGND
VIN
PGND
LX
AGND
8
7
6
5
C2
4.7µF
GND
LX
U1 AAT2146W SC70JW-8
L1 CDRH3D16-4R7
C2 4.7µF 10V 0805 X5R
C1 10µF 6.3V 0805 X5R
Figure 5: AAT2146W Adjustable Evaluation Board Schematic.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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13
DATA SHEET
AAT2146W
Low-Noise, Fast Transient 600mA Step-Down Converter
Layout
4.
The suggested PCB layout for the AAT2146W is shown in
Figures 2, 3, and 4. The following guidelines should be
used to help ensure a proper layout.
1.
2.
3.
14
Connect the input capacitor (C2) as close as possible
to VIN (Pin 3) and PGND (Pins 6-8).
Connect C1 and L1 as close as possible to the device
pins. The connection of L1 to the LX pin should be as
short as possible.
Separate the feedback trace or OUT pin (Pin 2) from
any power trace and connect as close as possible to
the load point. Sensing along a high-current load
trace will degrade DC load regulation. If external
feedback resistors are used, place them as close as
possible to the OUT pin (Pin 2) to minimize the
length of the high impedance feedback trace.
Keep the resistance of the trace from the load return
to the PGND (Pins 6-8) 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. More care must be taken when laying out the
copper board. For example, a non-shielded inductor will
have a larger radiated magnetic field than a shielded
inductor. Comparatively, the feedback trace must be
placed further away from the non-shielded inductor.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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DATA SHEET
AAT2146W
Low-Noise, Fast Transient 600mA Step-Down Converter
Step-Down Converter Design Example
Specifications
VO = 1.8V @ 400mA, Pulsed Load ILOAD = 300mA
VIN = 2.7V to 4.2V (3.6V nominal)
fsw = 2MHz
TA = 85°C
1.8V Output Inductor
L1 = 3
µs
µs
· VO = 3
· 1.8V = 5.4µH (use 4.7μH; see Table 1)
A
A
For Sumida inductor CDRH3D16, 4.7μH, DCR = 105m.
ΔIL1 =
VO
V
· 1- O
L1 . fsw
VIN
IPKL1 = IO +
=
1.8V
1.8V
· 14.7µH × 2.0MHz
4.2V
= 109mA
ΔIL1
= 0.4A + 0.055A = 0.455A
2
PL1 = IO2 · DCR = (0.4A)2 · 105mΩ = 17mW
1.8V Output Capacitor
VDROOP = 0.1V
COUT =
3 · ΔILOAD
3 · 0.3A
=
= 4.5µF; use 4.7µF
VDROOP · fsw
0.1V · 2.0MHz
IRMS =
(VO) · (VIN(MAX) - VO)
1
1.8V · (4.2V - 1.8V)
·
= 32mA (rms)
=
4.7µH
· 2.0MHz · 4.2V
f
·
V
L1
·
2· 3
2· 3
sw
IN(MAX)
1
·
PESR = ESR · IRMS2 = 5mΩ · (32mA)2 = 5.1µW
Input Capacitor
Input Ripple Voltage VPP = 25mV
CIN =
IRMS =
1
VPP
- ESR · 4 · fsw
IO
=
1
25mV
- 5mΩ · 4 · 2.0MHz
0.4A
= 2.17µF; use 2.2µF
IO
= 0.2A (rms)
2
PESR = ESR · IRMS2 = 5mΩ · (0.2A)2 = 0.2mW
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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15
DATA SHEET
AAT2146W
Low-Noise, Fast Transient 600mA Step-Down Converter
AAT2146W Losses
PTOTAL =
=
IO2 · (RDS(ON)HS · VO + RDS(ON)LS · [VIN -VO])
VIN
+ (tsw · fsw · IO + IQ) · VIN
0.42 · (0.38Ω · 1.8V + 0.30Ω · [4.2V - 1.8V])
4.2V
+ (5ns · 2.0MHz · 0.4A + 150µA) · 4.2V = 70.9mW
TJ(MAX) = TA + ΘJA · PLOSS = 85°C + (160°C/W) · 70.9mW = 96.4°C
16
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DATA SHEET
AAT2146W
Low-Noise, Fast Transient 600mA Step-Down Converter
VOUT (V)
R2 = 59k
R1 (k)
R2 = 221k1
R1 (k)
L1 (μH)
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.8
1.85
2.0
2.5
3.3
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
267
75.0
113
150
187
221
261
301
332
442
464
523
715
1000
2.2
2.2
2.2
2.2
2.2
2.2
4.7
4.7
4.7
4.7
6.8
6.8
6.8
Table 3: Evaluation Board Component Values.
Manufacturer
Sumida
Murata
Coilcraft
Coiltronics
TDK
Wurth
Part Number
Inductance (μH)
Max DC
Current (A)
DCR ()
Size (mm)
LxWxH
Type
CDRH3D16-2R2
CDRH3D16-4R7
CDRH3D16-6R8
LQH2MCN4R7M02
LQH32CN4R7M23
LPO3310-472
SD3118-4R7
SD3118-6R8
SDRC10-4R7
VLS3015T-4R7MR99
VLS3015T-6R8MR86
744042006
2.2
4.7
6.8
4.7
4.7
4.7
4.7
6.8
4.7
4.7
6.8
6.8
1.20
0.90
0.73
0.40
0.45
0.80
0.98
0.82
1.30
0.99
0.86
1.25
0.072
0.105
0.170
0.80
0.20
0.27
0.122
0.175
0.122
0.136
0.176
0.100
3.8x3.8x1.8
3.8x3.8x1.8
3.8x3.8x1.8
2.0x1.6x0.95
2.5x3.2x2.0
3.2x3.2x1.0
3.1x3.1x1.85
3.1x3.1x1.85
5.7x4.4x1.0
3.0x3.0x1.5
3.0x3.0x1.5
4.8x4.8x1.8
Shielded
Shielded
Shielded
Non-Shielded
Non-Shielded
1mm
Shielded
Shielded
1mm Shielded
Shielded
Shielded
Shielded
Table 4: Recommended Typical Surface Mount Inductors.
Manufacturer
Part Number
Value
Voltage
Temp. Co.
Case
Murata
Murata
Murata
GRM219R61A475KE19
GRM21BR60J106KE19
GRM21BR60J226ME39
4.7μF
10μF
22μF
10V
6.3V
6.3V
X5R
X5R
X5R
0805
0805
0805
Table 5: Recommended Surface Mount Capacitors.
1. For reduced quiescent current, R2 = 221k.
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17
DATA SHEET
AAT2146W
Low-Noise, Fast Transient 600mA Step-Down Converter
Ordering Information
Output Voltage1
Package
Marking2
Part Number (Tape and Reel)3
Adj  0.6
SC70JW-8
Q9XYY
AAT2146WIJS-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
2.20 ± 0.20
1.75 ± 0.10
0.50 BSC 0.50 BSC 0.50 BSC
0.225 ± 0.075
2.00 ± 0.20
0.100
7° ± 3°
0.45 ± 0.10
4° ± 4°
0.05 ± 0.05
0.15 ± 0.05
1.10 MAX
0.85 ± 0.15
0.048REF
2.10 ± 0.30
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.
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18
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