Skyworks AAT1147 Fast load transient Datasheet

DATA SHEET
AAT1147
High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter
General Description
Features
The AAT1147 SwitchReg is a member of Skyworks' Total
Power Management IC™ (TPMIC™) product family. It is
a fixed frequency 1.4MHz step-down converter with an
input voltage range of 2.7V to 5.5V and output voltage
as low as 0.6V.
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The AAT1147 is optimized for low noise portable applications, reacts quickly to load variations, and reaches peak
efficiency at heavy load.
The AAT1147 output voltage is programmable with
external feedback resistors. It can deliver 400mA of load
current while maintaining high power efficiency. The
1.4MHz switching frequency minimizes the size of external components while keeping switching losses low.
The AAT1147 is available in a Pb-free, space-saving
2.0x2.1mm SC70JW-8 package and is rated over the
-40°C to +85°C temperature range.
VIN Range: 2.7V to 5.5V
VOUT Adjustable from 0.6V to VIN
400mA Output Current
Up to 98% Efficiency
Low Noise, 1.4MHz Fixed Frequency PWM Operation
Fast Load Transient
150μs Soft Start
Over-Temperature and Current Limit Protection
100% Duty Cycle Low Dropout Operation
<1μA Shutdown Current
8-Pin SC70JW 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
VIN
3
1
C2
4.7µF
VO = 1.8V
U1
AAT1147
5
8
VIN
LX
EN
OUT
AGND
PGND
PGND
PGND
4
2
L1
4.7µH
118k
7
6
R1
R2
59k
C1
4.7µF
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012
1
DATA SHEET
AAT1147
High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter
Pin Descriptions
Pin #
Symbol
1
2
3
EN
OUT
VIN
4
LX
5
6, 7, 8
AGND
PGND
Function
Enable pin.
Feedback input pin. This pin is connected 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 connected internally to the drain of both highand 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)
EN
OUT
VIN
LX
2
1
8
2
7
3
6
4
5
PGND
PGND
PGND
AGND
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201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012
DATA SHEET
AAT1147
High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter
Absolute Maximum Ratings1
Symbol
VIN
VLX
VOUT
VEN
TJ
TLEAD
Description
Input Voltage to GND
LX to GND
OUT to GND
EN to GND
Operating Junction Temperature Range
Maximum Soldering Temperature (at leads, 10 sec.)
Value
Units
6.0
-0.3 to VIN + 0.3
-0.3 to VIN + 0.3
-0.3 to 6.0
-40 to 150
300
V
V
V
V
°C
°C
Value
Units
0.625
160
W
°C/W
Thermal Information2
Symbol
PD
JA
Description
Maximum Power Dissipation3
Thermal Resistance
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 • [email protected] • www.skyworksinc.com
201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012
3
DATA SHEET
AAT1147
High Efficiency, Low Noise, Fast Transient 400mA 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
IQ
ISHDN
ILIM
RDS(ON)H
RDS(ON)L
ILXLEAK
VLINEREG
VOUT
IOUT
TS
FOSC
TSD
THYS
EN
VEN(L)
VEN(H)
IEN
UVLO Threshold
Output Voltage Tolerance
Output Voltage Range
Quiescent Current
Shutdown Current
P-Channel Current Limit
High Side Switch On Resistance
Low Side Switch On Resistance
LX Leakage Current
Line Regulation
Out Threshold Voltage Accuracy
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
IOUT = 0 to 400mA, VIN = 2.7V to 5.5V
Max
Units
5.5
2.7
V
V
mV
V
%
V
μA
μA
mA


μA
%/V
mV
μA
μs
MHz
°C
°C
100
1.8
-3.0
0.6
No Load
EN = AGND = PGND
160
3.0
VIN
300
1.0
600
0.45
0.40
VIN = 5.5V, VLX = 0 to VIN, EN = GND
VIN = 2.7V to 5.5V
0.6V Output, No Load, TA = 25°C
0.6V Output
From Enable to Output Regulation
1
591
1.0
0.1
600
150
1.4
140
15
609
0.2
2.0
0.6
VIN = VOUT = 5.5V
1.4
-1.0
1.0
V
V
μA
1. The AAT1147 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
201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012
DATA SHEET
AAT1147
High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter
Typical Characteristics
Efficiency vs. Load
DC Regulation
(VOUT = 3.3V; L = 6.8µH)
(VOUT = 3.3V)
100
2.0
VIN = 3.6V
1.5
Output Error (%)
Efficiency (%)
80
60
VIN = 4.2V
40
VIN = 5.0V
20
1.0
VIN = 4.2V
0.5
0.0
-0.5
VIN = 3.6V
-1.0
VIN = 5.0V
-1.5
-2.0
0
1
10
100
1000
0.1
1
Output Current (mA)
100
1000
Output Current (mA)
Efficiency vs. Load
DC Regulation
(VOUT = 2.5V; L = 6.8µH)
(VOUT = 2.5V)
100
2.0
1.5
Output Error (%)
VIN = 3.6V
80
Efficiency (%)
10
60
VIN = 4.2V
40
VIN = 5.0V
20
1.0
VIN = 4.2V
0.5
0.0
-0.5
VIN = 5.0V
-1.0
VIN = 3.6V
-1.5
0
1
10
100
-2.0
0.1
1000
1
Output Current (mA)
100
1000
Output Current (mA)
Efficiency vs. Load
DC Regulation
(VOUT = 1.8V; L = 4.7µH)
(VOUT = 1.8V)
100
2.0
1.5
Output Error (%)
VIN = 3.0V
80
Efficiency (%)
10
60
VIN = 3.6V
40
VIN = 4.2V
20
1.0
VIN = 4.2V
0.5
0.0
VIN = 3.6V
-0.5
-1.0
VIN = 3.0V
-1.5
0
1
10
100
Output Current (mA)
1000
-2.0
0.1
1
10
100
1000
Output Current (mA)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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5
DATA SHEET
AAT1147
High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter
Typical Characteristics
Line Regulation
Line Regulation
(VOUT = 3.3V)
0.5
0.4
0.4
0.3
0.3
IOUT = 10mA IOUT = 1mA
0.2
Accuracy (%)
Accuracy (%)
(VOUT = 2.5V)
0.5
0.1
0
-0.1
-0.2
IOUT = 400mA
-0.3
IOUT = 10mA IOUT = 1mA
0.2
0.1
0.0
-0.1
-0.2
IOUT = 400mA
-0.3
-0.4
-0.4
-0.5
-0.5
3.0
3.2
3.4
3.6
3.8
4.0
4.2
4.4
4.6
4.8
5.0
3.0
3.2
3.4
3.6
Input Voltage (V)
3.8
4.0
4.2
4.4
4.6
4.8
5.0
Input Voltage (V)
Line Regulation
Frequency vs. Input Voltage
(VOUT = 1.8V)
0.5
Frequency Variation (%)
2.0
0.4
Accuracy (%)
0.3
0.2
0.1
IOUT = 10mA
0.0
IOUT = 1mA
-0.1
-0.2
-0.3
IOUT = 400mA
-0.4
-0.5
3.0
3.2
3.4
3.6
3.8
4.0
4.2
4.4
4.6
4.8
1.0
VOUT = 1.8V
0.0
-1.0
-2.0
VOUT = 2.5V
-3.0
-4.0
2.5
5.0
2.9
3.3
4.5
4.9
Output Voltage Error vs. Temperature
Switching Frequency vs. Temperature
(VIN = 3.6V; VOUT = 1.8V; IOUT = 400mA)
(VIN = 3.6V; VOUT = 1.8V)
2.0
15
1.5
12
0.5
0.0
-0.5
-1.0
-2.0
-40
5.3
9
1.0
6
3
0
-3
-6
-9
-1.5
-12
-15
-25
-10
5
20
35
50
Temperature (°°C)
6
4.1
Input Voltage (V)
Variation (%)
Output Error (%)
Input Voltage (V)
3.7
VOUT = 3.3V
65
80
95
-40
-25
-10
5
20
35
50
65
Temperature (°°C)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012
80
95
DATA SHEET
AAT1147
High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter
Typical Characteristics
No-Load Quiescent Current
vs. Input Voltage
Line Transient Response
(40mA to 400mA; VIN = 3.6V; VOUT = 1.8V;
C1 = 4.7µF; CFF = 100pF)
220
190
85°C
180
25°C
Output Voltage
(top) (V)
Supply Current (µA)
200
170
160
-40°C
150
140
130
120
2.0
1.4
1.9
1.2
1.8
1.0
1.7
0.8
1.6
0.6
1.5
0.4
1.4
0.2
400 mA
1.3
1.2
40 mA
1.1
2.5
3.0
3.5
4.0
4.5
5.0
1.0
5.5
1.4
1.9
1.2
1.8
1.0
1.7
0.8
1.6
0.6
1.5
0.4
1.4
0.2
0.0
400mA
40mA
1.0
-0.2
-0.4
-0.6
5.6
3.6
4.8
3.2
4.0
2.8
3.2
2.4
2.4
2.0
1.6
1.6
0.8
1.2
0.0
0.8
-0.8
0.4
-1.6
0.0
-2.4
-0.4
Time (25µs/div)
Output Ripple
(VIN = 3.6V; VOUT = 1.8V; IOUT = 400mA)
5.2
1.85
5.0
1.80
4.8
1.75
4.6
1.70
4.4
1.65
4.2
1.60
4.0
1.55
3.8
1.50
3.6
1.45
3.4
1.40
3.2
Time (25µs/div)
40
0.9
20
0.8
0
0.7
-20
0.6
-40
0.5
-60
0.4
-80
0.3
-100
0.2
-120
0.1
Inductor Current
(bottom) (A)
1.90
Output Voltage
(AC Coupled) (top) (mV)
Line Response
(VOUT = 1.8V @ 400mA)
Input Voltage
(bottom) (V)
Output Voltage
(top) (V)
Time (25µs/div)
Inductor Current
(bottom) (A)
2.0
Enable and Output Voltage
(top) (V)
(VIN = 3.6V; VOUT = 1.8V; IOUT = 400mA)
Load and Inductor Current
(bottom) (200mA/div)
Output Voltage
(top) (V)
Soft Start
(40mA to 400mA; VIN = 3.6V;
VOUT = 1.8V; C1 = 4.7µF)
1.1
-0.4
-0.6
Line Transient Response
1.2
-0.2
Time (25µs/div)
Input Voltage (V)
1.3
0.0
Load and Inductor Current
(bottom) (200mA/div)
210
Time (500ns/div)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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7
DATA SHEET
AAT1147
High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter
Functional Block Diagram
VIN
OUT
Err
Amp
.
DH
Voltage
Reference
EN
INPUT
LX
Logic
DL
PGND
AGND
Functional Description
The AAT1147 is a high performance 400mA 1.4MHz
monolithic step-down converter. It has been designed
with the goal of minimizing external component size and
optimizing efficiency at heavy load. 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).
Only three external power components (CIN, COUT, and L)
are required. Output voltage is programmed with external resistors and ranges from 0.6V to the input voltage.
An additional feed-forward capacitor can also be added
8
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 RDS(ON) drop of the P-channel high-side MOSFET.
The input voltage range is 2.7V to 5.5V. The converter
efficiency has been optimized for heavy load conditions
up to 400mA.
The internal error amplifier and compensation provide
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
201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012
DATA SHEET
AAT1147
High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter
1
2
3
Enable
VIN
C4
100pF
U1
AAT1147
1
VOUT =1.8V
R1
2
L1 118k
4.7μH
3
4
C1
10μF
C3
n/a
R2
59k
EN
PGND
OUT
PGND
VIN
PGND
LX
AGND
8
7
6
5
C2
4.7μF
GND
LX
GND2
U1 AAT1147 SC70JW-8
L1 CDRH3D16-4R7
C2 4.7μF 10V 0805 X5R
C1 10μF 6.3V 0805 X5R
Figure 1: Enhanced Transient Response Schematic.
Control Loop
The AAT1147 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.
Current Limit and
Over-Temperature Protection
For overload conditions, the peak input current is limited. 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.
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. The
error amplifier reference is 0.6V.
Thermal protection completely disables switching when
internal dissipation becomes excessive. The junction
over-temperature threshold is 140°C with 15°C of hysteresis. Once an over-temperature or over-current fault
conditions is removed, the output voltage automatically
recovers.
Soft Start / Enable
Under-Voltage Lockout
Soft start limits the current surge seen at the input and
eliminates output voltage overshoot. When pulled low,
the enable input forces the AAT1147 into a low-power,
non-switching state. The total input current during shutdown is less than 1μA.
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.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012
9
DATA SHEET
AAT1147
High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter
Applications Information
for C. The calculated value varies with input voltage and
is a maximum when VIN is double the output voltage.
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 for the AAT1147 is
0.24A/μsec. 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 ⋅ VO 0.75 ⋅ 1.5V
A
m=
=
= 0.24
L
4.7μH
μsec
This is the internal slope compensation. When externally
programming the 0.6V version to 2.5V, the calculated
inductance is 7.5μH.
L=
0.75 ⋅ VO
=
m
=3
μsec
0.75 ⋅ VO
≈ 3 A ⋅ VO
A
0.24A μsec
μsec
⋅ 2.5V = 7.5μH
A
In this case, a standard 6.8μH value is selected.
CIN =
V ⎞
VO ⎛
· 1- O
VIN ⎝
VIN ⎠
⎛ VPP
⎞
- ESR · FS
⎝ IO
⎠
VO ⎛
V ⎞
1
· 1 - O = for VIN = 2 · VO
VIN ⎝
VIN ⎠
4
CIN(MIN) =
1
⎛ VPP
⎞
- ESR · 4 · FS
⎝ 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.
Configuration
Output Voltage
Inductor
0.6V Adjustable With
External Feedback
1V, 1.2V
1.5V, 1.8V
2.5V, 3.3V
2.2μH
4.7μH
6.8μH
Table 1: Inductor Values.
The maximum input capacitor RMS current is:
Table 1 displays inductor values for the AAT1147.
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.
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.
IRMS = IO ·
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 ⎠
Select a 4.7μF to 10μF X7R or X5R ceramic capacitor for
the input. To estimate the required input capacitor size,
determine the acceptable input ripple level (VPP) and solve
10
D · (1 - D) =
0.52 =
1
2
for VIN = 2 · VO
IRMS(MAX) =
VO
Input Capacitor
VO ⎛
V ⎞
· 1- O
VIN ⎝
VIN ⎠
IO
2
⎛
V ⎞
· 1- O
The term VIN ⎝ VIN ⎠ 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.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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DATA SHEET
AAT1147
High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter
The input capacitor provides a low impedance loop for
the edges of pulsed current drawn by the AAT1147. 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.
Figure 2: AAT1147 Evaluation Board
Top Side.
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.
Figure 3: Exploded View of Evaluation
Board Top Side Layout.
Figure 4: AAT1147 Evaluation Board
Bottom Side.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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11
DATA SHEET
AAT1147
High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter
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 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 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 · FS
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) =
12
1
VOUT · (VIN(MAX) - VOUT)
L · FS · 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.
Output Resistor Selection
The output voltage of the AAT1147 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 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.
⎛ VOUT ⎞
⎛ 1.5V ⎞
R1 = V
-1 · R2 = 0.6V - 1 · 59kΩ = 88.5kΩ
⎝ REF ⎠
⎝
⎠
The AAT1147, combined with an external feedforward
capacitor (C4 in Figure 1), delivers enhanced transient
response for extreme pulsed load applications. The addition of the feedforward capacitor typically requires a
larger output capacitor C1 for stability.
VOUT (V)
R2 = 59kΩ
R1 (kΩ)
R2 = 221kΩ
R1 (kΩ)
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
Table 2: Resistor Values For Use With
0.6V Step-Down Converter.
·
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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DATA SHEET
AAT1147
High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter
1
2
3
Enable
VIN
U1
AAT1147
1
R1
VOUT
C1
10μF
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
GND2
LX
U1 AAT1147 SC70JW-8
L1 CDRH3D16-4R7
C1 10μF 10V 0805 X5R
C2 4.7μF 10V 0805 X5R
Figure 5: AAT1147 Evaluation Board Schematic.
Thermal Calculations
For the condition where the step-down converter is in
dropout at 100% duty cycle, the total device dissipation
reduces to:
There are three types of losses associated with the
AAT1147 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 switching devices. At full load, assuming continuous conduction
mode (CCM), a simplified form of the losses is given by:
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.
IQ is the step-down converter quiescent current. The
term tsw is used to estimate the full load step-down converter switching losses.
Given the total losses, the maximum junction temperature can be derived from the JA for the SC70JW-8 package which is 160°C/W.
PTOTAL =
IO2 · (RDSON(H) · VO + RDSON(L) · [VIN - VO])
PTOTAL = IO2 · RDSON(H) + IQ · VIN
TJ(MAX) = PTOTAL · ΘJA + TAMB
VIN
+ (tsw · FS · IO + IQ) · VIN
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13
DATA SHEET
AAT1147
High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter
Layout
The suggested PCB layout for the AAT1147 is shown in
Figures 2, 3, and 4. The following guidelines should be
used to help ensure a proper layout.
1.
2.
3.
4.
14
The input capacitor (C2) should connect as closely as
possible to VIN (Pin 3) and PGND (Pins 6-8).
C1 and L1 should be connected as closely as possible. The connection of L1 to the LX pin should be as
short as possible.
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 regulation. External feedback resistors should be placed as
closely as possible to the OUT pin (Pin 2) to minimize
the length of the high impedance feedback trace.
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.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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DATA SHEET
AAT1147
High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter
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 = 1.4MHz
TAMB = 85°C
1.8V Output Inductor
L1 = 3
μsec
μsec
⋅ VO2 = 3
⋅ 1.8V = 5.4μH (use 4.7μH; see Table 1)
A
A
For Sumida inductor CDRH3D16, 4.7μH, DCR = 105m.
ΔIL1 =
⎛
VO
V ⎞
1.8V
1.8V ⎞
⎛
⋅ 1- O =
⋅ 1= 156mA
L1 ⋅ FS ⎝ VIN⎠ 4.7μH ⋅ 1.4MHz ⎝
4.2V ⎠
IPKL1 = IO +
ΔIL1
= 0.4A + 0.068A = 0.468A
2
PL1 = IO2 ⋅ DCR = 0.4A2 ⋅ 105mΩ = 17mW
1.8V Output Capacitor
VDROOP = 0.1V
COUT =
3 · ΔILOAD
3 · 0.3A
=
= 6.4μF; use 10µF
0.1V · 1.4MHz
VDROOP · FS
IRMS =
(VO) · (VIN(MAX) - VO)
1
1.8V · (4.2V - 1.8V)
·
= 45mArms
=
L1 · FS · VIN(MAX)
2 · 3 4.7μH · 1.4MHz · 4.2V
2· 3
1
·
Pesr = esr · IRMS2 = 5mΩ · (45mA)2 = 10μW
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15
DATA SHEET
AAT1147
High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter
Input Capacitor
Input Ripple VPP = 25mV
CIN =
IRMS =
⎛ VPP
⎝ IO
1
1
=
= 3.11μF; use 4.7μF
⎞
⎛ 25mV
⎞
- 5mΩ · 4 · 1.4MHz
- ESR · 4 · FS
⎠
⎝ 0.4A
⎠
IO
= 0.2Arms
2
P = esr · IRMS2 = 5mΩ · (0.2A)2 = 0.2mW
AAT1147 Losses
PTOTAL =
IO2 · (RDSON(H) · VO + RDSON(L) · [VIN -VO])
VIN
+ (tsw · FS · IO + IQ) · VIN
TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (160°C/W) · 126mW = 105.1°C
16
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DATA SHEET
AAT1147
High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter
Adjustable Version
(0.6V device)
VOUT (V)
R2 = 59kΩ
R1 (kΩ)
R2 = 221kΩ1
R1 (kΩ)
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
Part Number
Inductance
(μH)
Max DC
Current (A)
DCR (Ω)
Size (mm)
LxWxH
Type
Sumida
Sumida
Sumida
Murata
Murata
Coilcraft
Coiltronics
Coiltronics
Coiltronics
CDRH3D16-2R2
CDRH3D16-4R7
CDRH3D16-6R8
LQH2MCN4R7M02
LQH32CN4R7M23
LPO3310-472
SD3118-4R7
SD3118-6R8
SDRC10-4R7
2.2
4.7
6.8
4.7
4.7
4.7
4.7
6.8
4.7
1.20
0.90
0.73
0.40
0.45
0.80
0.98
0.82
1.30
0.072
0.105
0.170
0.80
0.20
0.27
0.122
0.175
0.122
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
Shielded
Shielded
Shielded
Non-Shielded
Non-Shielded
1mm
Shielded
Shielded
1mm Shielded
Table 4: 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: Surface Mount Capacitors.
1. For reduced quiescent current, R2 and R4 = 221kW.
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17
DATA SHEET
AAT1147
High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
SC70JW-8
SCXYY
AAT1147IJS-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. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
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