AAT1143IJS-3.3-T1 [SKYWORKS]
1MHz 400mA Step-Down Converter; 1MHz的400毫安降压转换器
| 型号： | AAT1143IJS-3.3-T1 |
| 厂家： | 
SKYWORKS SOLUTIONS INC. |
| 描述： | 1MHz 400mA Step-Down Converter |
| 文件： | 总19页 (文件大小：1138K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
General Description
Features
•
•
The AAT1143 SwitchReg™ is a 1MHz step-down con-
verter with an input voltage range of 2.7V to 5.5V and
output as low as 0.6V. Its low supply current, small size,
and high switching frequency make the AAT1143 the
ideal choice for portable applications.
VIN Range: 2.7V to 5.5V
VOUT Adjustable Down to 0.6V
Fixed or Adjustable Version
25μA No Load Quiescent Current
Up to 95% Efficiency
▪
•
•
•
•
•
•
•
•
•
•
•
400mA Max Output Current
1MHz Switching Frequency
Soft Start
Over-Temperature Protection
Current Limit Protection
100% Duty Cycle Low-Dropout Operation
0.1μA Shutdown Current
SC70JW-8 Package
The AAT1143 is available in either a fixed version with
internal feedback or a programmable version with exter-
nal feedback resistors. It can deliver 400mA of load cur-
rent while maintaining a low 25μA no load quiescent
current. The 1MHz switching frequency minimizes the
size of external components while keeping switching
losses low. The AAT1143 feedback and control delivers
excellent load regulation and transient response with a
small output inductor and capacitor.
Temperature Range: -40°C to +85°C
The AAT1143 is designed to maintain high efficiency
throughout the operating range, which is critical for por-
table applications.
Applications
•
•
•
•
•
•
Cellular Phones
Digital Cameras
Handheld Instruments
Microprocessor / DSP Core / IO Power
PDAs and Handheld Computers
USB Devices
The AAT1143 is available in a space-saving 2.0 x 2.2mm
SC70JW-8 package and is rated over the -40°C to +85°C
temperature range.
Typical Application (Fixed Output Voltage)
Efficiency vs. Load Current
(VOUT = 2.5V; VIN = 3.3V)
VO
VIN
U1
AAT1143
100
95
90
85
80
75
70
65
60
L1
3
1
5
8
4
2
7
6
LX
VIN
4.7μH
OUT
PGND
PGND
EN
C2
4.7μF
C1
4.7μF
AGND
PGND
0.1
1
10
100
1000
Output Current (mA)
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DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
Pin Descriptions
Pin #
Symbol
Function
1
EN
Enable pin.
Feedback input pin. This pin is connected either directly to the converter output or to an external resis-
tive 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.
2
3
4
OUT
VIN
LX
5
AGND
PGND
Non-power signal ground pin.
Main power ground return pin. Connect to the output and input capacitor return.
6, 7, 8
Pin Configuration
SC70JW-8
(Top View)
8
7
6
5
1
2
3
4
PGND
PGND
PGND
AGND
EN
OUT
VIN
LX
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DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
Absolute Maximum Ratings1
Symbol
Description
Value
Units
VIN
VLX
VOUT
VEN
TJ
Input Voltage GND
LX to GND
OUT to GND
EN to GND
Operating Junction Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
6.0
V
V
V
V
°C
°C
-0.3 to VP + 0.3
-0.3 to VP + 0.3
-0.3 to 6.0
-40 to 150
300
TLEAD
Thermal Information
Symbol
Description
Value
Units
PD
JA
Maximum Power Dissipation (SC70JW-8)
Thermal Resistance2 (SC70JW-8)
625
160
mW
°C/W
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions
specified is not implied. Only one Absolute Maximum Rating should be applied at any one time.
2. Mounted on an FR4 board.
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DATA SHEET
AAT1143
1MHz 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
Step-Down Converter
Conditions
Min Typ Max
Units
VIN
Input Voltage
2.7
5.5
2.6
V
V
VIN Rising
VUVLO
UVLO Threshold
Hysteresis
VIN Falling
100
25
mV
V
%
1.8
-3.0
0.6
VOUT
VOUT
Output Voltage Tolerance
Output Voltage Range
IOUT = 0 to 400mA, VIN = 2.7V to 5.5V
Fixed Output Version
Adjustable Output Version2
No Load, 0.6V Adjustable Version
EN = AGND = PGND
+3.0
4.0
2.5
50
V
0.6
IQ
ISHDN
ILIM
RDS(ON)H
RDS(ON)L
ILXLEAK
VLinereg
VOUT
IOUT
ROUT
FOSC
TSD
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
Out Impedance
Oscillator Frequency
μA
μA
mA
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
>0.6V Output
TA = 25°C
1
μA
%/V
mV
μA
k
MHz
°C
0.2
615
0.2
597
600
250
0.7
1.0
140
15
1.5
Over-Temperature Shutdown Threshold
Over-Temperature Shutdown Hysteresis
THYS
°C
EN
VEN(L)
VEN(H)
IEN
Enable Threshold Low
Enable Threshold High
Input Low Current
0.6
1.0
V
V
μA
1.4
-1.0
VIN = VFB = 5.5V
1. The AAT1143 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and correla-
tion with statistical process controls.
2. For adjustable version with higher than 2.5V output, please consult your Skyworks representative.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
Typical Characteristics
Efficiency vs. Load
(VOUT = 2.5V; L = 4.7μH)
Load Regulation
(VOUT = 2.5V; L = 4.7μH)
100
2.0
VIN = 3.3V
VIN = 3.0V
90
80
70
60
1.0
VIN = 3.0V
VIN = 3.6V
0.0
VIN = 3.3V
-1.0
VIN = 3.6V
-2.0
0.1
1
10
100
1000
0.1
1
10
100
1000
1000
100
Output Current (mA)
Output Current (mA)
Efficiency vs. Load
(VOUT = 1.8V; L = 4.7μH)
DC Regulation
(VOUT = 1.8V; L = 4.7μH)
100
90
80
70
60
50
2.0
1.0
VIN = 3.6V
VIN = 2.7V
VIN = 4.2V
0.0
VIN = 4.2V
VIN = 2.7V
-1.0
-2.0
VIN = 3.6V
0.1
1
10
100
1000
0.1
1
10
100
Output Current (mA)
Output Current (mA)
Frequency vs. Input Voltage
(VOUT = 1.8V)
Output Voltage Error vs. Temperature
(VIN = 3.6V; VO = 1.5V)
2.0
1.0
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
0.0
-1.0
-2.0
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
-40
-20
0
20
40
60
80
Input Voltage (V)
Temperature (°°C)
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DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
Typical Characteristics
Switching Frequency vs. Temperature
(VIN = 3.6V; VO = 1.5V)
Quiescent Current vs. Input Voltage
(VO = 1.8V)
0.20
0.10
35
85°C
30
25°C
0.00
25
20
-0.10
-40°C
15
-0.20
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
-40
-20
0
20
40
60
80
100
Temperature (°C)
Input Voltage (V)
P-Channel RDS(ON) vs. Input Voltage
N-Channel RDS(ON) vs. Input Voltage
750
750
700
650
600
550
500
450
400
350
300
700
650
600
550
500
450
400
350
300
120°C
100°C
120°C
100°C
85°C
85°C
25°C
25°C
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Input Voltage (V)
Input Voltage (V)
Load Transient Response
(30mA to 300mA; VIN = 3.6V; VOUT = 1.8V; C1 = 10μF)
Load Transient Response
(30mA to 300mA; VIN = 3.6V; VOUT = 1.8V;
C1 = 10μμF; C4 = 100pF; see Figure 1)
0.1
0.0
1.4
1.2
1.4
1.2
1.0
0.8
0.6
0.4
0.2
2.0
1.9
1.8
1.7
300mA
-0.1
1.0
0.8
0.6
0.4
300mA
-0.2
-0.3
-0.4
-0.5
-0.6
-0.7
30mA
1.6
1.5
30mA
1.4
0.2
0.0
-0.2
1.3
1.2
0.0
-0.2
Time (25μs/div)
Time (25μs/div)
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DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
Typical Characteristics
Load Transient Response
(30mA to 300mA; VIN = 3.6V; VOUT = 1.8V; C1 = 4.7μF)
Line Transient
(VOUT = 1.8V @ 400mA)
1.90
1.85
1.80
1.75
1.70
1.65
1.60
1.55
1.50
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
1.4
1.2
1.0
0.8
0.6
0.4
0.2
2.0
1.9
1.8
1.7
300mA
1.6
1.5
30mA
1.4
1.3
1.2
0.0
-0.2
Time (25μs/div)
Time (25μs/div)
Line Regulation
(VOUT = 1.8V)
Soft Start
(VIN = 3.6V; VOUT = 1.8V; 400mA)
0.1
4.0
3.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
-0.5
0.05
0
IOUT = 100mA
2.0
-0.05
-0.1
-0.15
-0.2
-0.25
-0.3
-0.35
1.0
IOUT = 10mA
0.0
-1.0
-2.0
-3.0
-4.0
IOUT = 400mA
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Time (250μs/div)
Input Voltage (V)
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DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
Functional Block Diagram
VIN
OUT
See note
Err
Amp
.
DH
LX
Voltage
Logic
Reference
DL
INPUT
EN
PGND
AGND
Note: For adjustable version, the internal feedback divider is omitted and the FB pin is tied directly
to the internal error amplifier.
tional feed-forward capacitor can also be added to the
external feedback to provide improved transient response
(see Figure 1).
Functional Description
The AAT1143 is a high performance 400mA 1MHz mono-
lithic step-down converter. It has been designed with the
goal of minimizing external component size and optimiz-
ing efficiency over the complete load range. 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).
At dropout, the converter duty cycle increases to 100%
and the output voltage tracks the input voltage minus
the RDSON drop of the P-channel high-side MOSFET.
The input voltage range is 2.7V to 5.5V. The converter
efficiency has been optimized for all load conditions,
ranging from no load to 400mA.
The fixed output version requires only three external
power components (CIN, COUT, and L). The adjustable ver-
sion can be programmed with external feedback to any
voltage, ranging from 0.6V to the input voltage. An addi-
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.
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DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
1
2
3
Enable
VIN
C4
100pF
U1
AAT1143
1
2
3
4
8
VOUT =1.8V
PGND
EN
R1
118k
7
6
5
OUT PGND
PGND
AGND
VIN
LX
L1
4.7μH
C1
10μF
C2
4.7μF
R2
59k
GND
LX
GND2
U1 AAT1143 SC70JW-8
L1 CDRH3D16-4R7
C2 4.7μF 10V 0805 X5R
C1 10μF 6.3V 0805 X5R
Figure 1: Enhanced Transient Response Schematic.
non-switching state. The total input current during shut-
down is less than 1μA.
Control Loop
The AAT1143 is a peak current mode step-down con-
verter. The current through the P-channel MOSFET (high
side) is sensed for current loop control, as well as short
circuit and overload protection. A fixed slope compensa-
tion signal is added to the sensed current to maintain
stability for duty cycles greater than 50%. The peak cur-
rent mode loop appears as a voltage-programmed cur-
rent source in parallel with the output capacitor.
Current Limit and
Over-Temperature Protection
For overload conditions, the peak input current is limit-
ed. To minimize power dissipation and stresses under
current limit and short-circuit conditions, switching is
terminated after entering current limit for a series of
pulses. Switching is terminated for seven consecutive
clock cycles after a current limit has been sensed for a
series of four consecutive clock cycles.
The output of the voltage error amplifier programs the
current mode loop for the necessary peak switch current
to force a constant output voltage for all load and line
conditions. Internal loop compensation terminates the
transconductance voltage error amplifier output. For
fixed voltage versions, the error amplifier reference volt-
age is internally set to program the converter output
voltage. For the adjustable output, the error amplifier
reference is fixed at 0.6V.
Thermal protection completely disables switching when
internal dissipation becomes excessive. The junction
over-temperature threshold is 140°C with 15°C of hys-
teresis. Once an over-temperature or over-current fault
conditions is removed, the output voltage automatically
recovers.
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 AAT1143 into a low-power,
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.
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DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
Input Capacitor
Applications Information
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
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 con-
trol with slope compensation to maintain stability for
duty cycles greater than 50%. The output inductor value
must be selected so the inductor current down slope
meets the internal slope compensation requirements.
The internal slope compensation for the adjustable and
low-voltage fixed versions of the AAT1143 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.
VO
VIN
⎛
VO ⎞
VIN ⎠
· 1 -
⎝
CIN =
⎛ VPP
⎝ IO
⎞
- ESR ·FS
⎠
VO
VIN
⎛
VO ⎞
VIN ⎠
1
· 1 -
=
for VIN = 2 · VO
⎝
4
0.75 ⋅ VO 0.75 ⋅ 1.5V
= 0.24
A
m =
=
1
L
4.7μH
μsec
CIN(MIN)
=
⎛ VPP
⎝ IO
⎞
⎠
- ESR · 4 · FS
This is the internal slope compensation for the adjust-
able (0.6V) version or low-voltage fixed versions. When
externally programming the 0.6V version to 2.5V, the
calculated inductance is 7.5μH.
Always examine the ceramic capacitor DC voltage coeffi-
cient 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.
0.75 ⋅ VO
0.75
⋅
VO
A
μsec
A
L =
=
≈
3
⋅ VO
m
0.24A
μsec
Output
Slope
Configuration Voltage Inductor Compensation
μsec
A
0.6V to
2.0V
2.5V
0.6V to
2.0V
= 3
⋅ 2.5V = 7.5μH
0.6V Adjustable
With External
Resistive Divider
4.7μH
10μH
4.7μH
0.24A/μsec
0.24A/μsec
0.24A/μsec
In this case, a standard 10μH value is selected.
Fixed Output
For high-voltage fixed versions (2.5V and above), m =
0.48A/μsec. Table 1 displays inductor values for the
AAT1143 fixed and adjustable options.
2.5V to
3.3V
4.7μH
0.48A/μsec
Table 1: Inductor Values.
The maximum input capacitor RMS current is:
Manufacturer’s specifications list both the inductor DC
current rating, which is a thermal limitation, and the
peak current rating, which is determined by the satura-
tion characteristics. The inductor should not show any
appreciable saturation under normal load conditions.
Some inductors may meet the peak and average current
ratings yet result in excessive losses due to a high DCR.
Always consider the losses associated with the DCR and
its effect on the total converter efficiency when selecting
an inductor.
VO
VIN
⎛
VO ⎞
VIN ⎠
IRMS = IO ·
· 1 -
⎝
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.
The 4.7μH CDRH3D16 series inductor selected from
Sumida has a 105mW DCR and a 900mA DC current rat-
ing. At full load, the inductor DC loss is 17mW which gives
a 2.8% loss in efficiency for a 400mA, 1.5V output.
VO
VIN
⎛
VO ⎞
VIN ⎠
1
2
· 1 -
⎝
=
D · (1 - D) = 0.52 =
for VIN = 2 · VO
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DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
VOUT
IO ⋅ k ⋅ F
⎛
VOUT
VIN
⎞
⎠
1.5
V
1.5V
4.2V
⎠
Output Capacitor
⎛
⎞
L =
⋅ 1 -
⎝
=
⋅ 1 -
⎝
= 4.82μH
0.4A ⋅ 0.4 ⋅ 1.25MHz
The output capacitor limits the output ripple and pro-
vides holdup during large load transitions. A 4.7μF to
10μF X5R or X7R ceramic capacitor typically provides
sufficient bulk capacitance to stabilize the output during
large load transitions and has the ESR and ESL charac-
teristics necessary for low output ripple.
VO
·
VIN
⎛
⎝
VO
VIN
⎞
⎠
1 -
The term
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.
The output voltage droop due to a load transient is
dominated by the capacitance of the ceramic output
capacitor. During a step increase in load current, the
ceramic output capacitor alone supplies the load current
until the loop responds. Within two or three switching
cycles, the loop responds and the inductor current
increases to match the load current demand. The rela-
tionship of the output voltage droop during the three
switching cycles to the output capacitance can be esti-
mated by:
The input capacitor provides a low impedance loop for
the edges of pulsed current drawn by the AAT1143. 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.
3 · ΔILOAD
=
COUT
A laboratory test set-up typically consists of two long
wires running from the bench power supply to the evalu-
ation board input voltage pins. The inductance of these
wires, along with the low-ESR ceramic input capacitor,
can create a high Q network that may affect converter
performance. This problem often becomes apparent in
the form of excessive ringing in the output voltage dur-
ing load transients. Errors in the loop phase and gain
measurements can also result.
VDROOP · FS
Once the average inductor current increases to the DC
load level, the output voltage recovers. The above equa-
tion establishes a limit on the minimum value for the
output capacitor with respect to load transients.
The internal voltage loop compensation also limits the
minimum output capacitor value to 4.7μF. This is due to
its effect on the loop crossover frequency (bandwidth),
phase margin, and gain margin. Increased output capac-
itance will reduce the crossover frequency with greater
phase margin.
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.
The maximum output capacitor RMS ripple current is
given by:
In applications where the input power source lead induc-
tance cannot be reduced to a level that does not affect
the converter performance, a high ESR tantalum or alu-
minum electrolytic should be placed in parallel with the
low ESR, ESL bypass ceramic. This dampens the high Q
network and stabilizes the system.
1
V
OUT · (VIN(MAX) - VOUT
)
IRMS(MAX)
=
·
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.
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DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
Figure 2: AAT1143 Evaluation Board
Top Side.
Figure 3: Exploded View of Evaluation
Board Top Side Layout.
Figure 4: AAT1143 Evaluation Board
Bottom Side.
R2 set to either 59k for good noise immunity or 221k
for reduced no load input current.
Adjustable Output Resistor Selection
For applications requiring an adjustable output voltage,
the 0.6V version can be externally programmed. Resistors
R1 and R2 of Figure 5 program the output to regulate at
a voltage higher than 0.6V. To limit the bias current
required for the external feedback resistor string while
maintaining good noise immunity, the minimum sug-
gested value for R2 is 59k. Although a larger value will
further reduce quiescent current, it will also increase the
impedance of the feedback node, making it more sensi-
tive to external noise and interference. Table 2 summa-
rizes the resistor values for various output voltages with
V
V
1.5V
0.6V
⎛
⎝
⎞
⎛
⎝
⎞
⎠
R1 =
OUT -1 · R2 =
- 1 · 59kΩ = 88.5kΩ
⎠
REF
The adjustable version of the AAT1143, 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.
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DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
Thermal Calculations
R2 = 59kΩ
R1 (kΩ)
R2 = 221kΩ
R1 (kΩ)
VOUT (V)
There are three types of losses associated with the
AAT1143 step-down converter: switching losses, con-
duction losses, and quiescent current losses. Conduction
losses are associated with the RDS(ON) characteristics of
the power output switching devices. Switching losses are
dominated by the gate charge of the power output
switching devices. At full load, assuming continuous con-
duction mode (CCM), a simplified form of the losses is
given by:
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.8
1.85
2.0
2.5
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
75
113
150
187
221
261
301
332
442
464
523
715
124
137
187
IO2 · (RDS(ON)H · VO + RDS(ON)L · [VIN - VO])
PTOTAL
=
VIN
Table 2: Adjustable Resistor Values For Use With
0.6V Step-Down Converter.
+ (tsw · FS · IO + IQ) · VIN
IQ is the step-down converter quiescent current. The
term tsw is used to estimate the full load step-down con-
verter switching losses.
1
2
3
Enable
VIN
C4
100pF
U1
AAT1143
1
2
3
4
8
7
6
5
EN
PGND
VOUT =1.8V
R1
118k
OUT PGND
L1
VIN
LX
PGND
AGND
4.7μH
C1
R2
59k
10μF
C2
4.7μF
C3
n/a
GND
LX
GND2
U1 AAT1143 SC70JW-8
L1 CDRH3D16-4R7
C2 4.7μF 10V 0805 X5R
C1 10μF 6.3V 0805 X5R
Figure 5: AAT1143 Adjustable Evaluation Board Schematic.
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DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
For the condition where the step-down converter is in
dropout at 100% duty cycle, the total device dissipation
reduces to:
Layout
The suggested PCB layout for the AAT1143 is shown in
Figures 2, 3, and 4. The following guidelines should be
used to help ensure a proper layout.
PTOTAL = IO2 · RDS(ON)H + IQ · VIN
1. The input capacitor (C2) should connect as closely as
possible to VIN (Pin 3) and PGND (Pins 6 through 8).
2. C1 and L1 should be connected as closely as possi-
ble. The connection of L1 to the LX pin should be as
short as possible.
Since RDS(ON), quiescent current, and switching losses all
vary with input voltage, the total losses should be inves-
tigated over the complete input voltage range.
3. The feedback trace or OUT pin (Pin 2) should be
separate from any power trace and connect as close-
ly as possible to the load point. Sensing along a
high-current load trace will degrade DC load regula-
tion. If external feedback resistors are used, they
should be placed as closely as possible to the OUT
pin (Pin 2) to minimize the length of the high imped-
ance feedback trace.
4. The resistance of the trace from the load return to
PGND (Pins 6 through 8) should be kept to a mini-
mum. 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.
Given the total losses, the maximum junction tempera-
ture can be derived from the JA for the SC70JW-8 pack-
age which is 160°C/W.
TJ(MAX) = PTOTAL · ΘJA + TAMB
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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DATA SHEET
AAT1143
1MHz 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 = 1.0MHz
TAMB = 85°C
1.8V Output Inductor
μsec
A
μsec
A
(see Table 1)
L1 = 3
⋅ VO2 = 3
⋅ 1.8V = 5.4μH
For Sumida inductor CDRH3D16, 4.7μH, DCR = 105mΩ.
⎛
⎝
⎞
1.8V
⎠
4.2V
VO
L1 ⋅ FS
VO
VIN
1.8
V
⎛
⎞
⎠
ΔIL1 =
⋅ 1 -
⎝
=
⋅ 1 -
= 218mA
4.7μH ⋅ 1.0MHz
ΔI
IPKL1 = IO + L1 = 0.4A + 0.11A = 0.51A
2
PL1 = IO2 ⋅ DCR = 0.4A2 ⋅ 105mΩ = 17mW
1.8V Output Capacitor
VDROOP = 0.2V
3 · ΔILOAD
VDROOP · FS
3 · 0.3A
COUT
=
=
= 4.5μF
0.2V · 1MHz
(VO) · (VIN(MAX) - VO)
L1 · FS · VIN(MAX)
1
1.8V · (4.2V - 1.8V)
1
·
= 63mArms
IRMS
=
·
=
4.7μH · 1.0MHz · 4.2V
2· 3
2· 3
Pesr = esr · IRMS2 = 5mΩ · (63mA)2 = 20μW
Input Capacitor
Input Ripple VPP = 25mV
1
1
CIN =
=
= 4.75μF
⎛ VPP
⎝ IO
⎞
⎛ 25mV
⎝ 0.4A
⎞
- ESR · 4 · FS
- 5mΩ · 4 · 1MHz
⎠
⎠
IO
IRMS
=
= 0.2Arms
2
P = esr · IRMS2 = 5mΩ · (0.2A)2 = 0.2mW
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DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
AAT1143 Losses
IO2 · (RDS(ON)H · VO + RDS(ON)L · [VIN -VO])
PTOTAL
=
VIN
+ (tsw · FS · IO + IQ) · VIN
0.42 · (0.725Ω · 1.8V + 0.7Ω · [4.2V - 1.8V])
4.2V
=
+ (5ns · 1.0MHz · 0.4A + 50μA) · 4.2V = 122mW
TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (160°C/W) · 122mW = 104.5°C
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DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
VOUT (V)
Adjustable Version
(0.6V device)
R1 (kΩ)
R2 = 59kΩ
R1 (kΩ)
R2 = 221kΩ1
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
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
75.0
113
150
187
221
261
301
332
442
464
523
715
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
124
137
187
4.7
4.7 or 6.8
10
VOUT (V)
Fixed Version
R1 (k)
R2 Not Used
L1 (μH)
0.6-3.3V
0
4.7
Table 3: Evaluation Board Component Values.
Inductance
Max DC
Current (A)
Size (mm)
LxWxH
Manufacturer
Part Number
(μH)
DCR ()
Type
Sumida
Sumida
Murata
Murata
Murata
Coilcraft
Coilcraft
Coiltronics
Coiltronics
Coiltronics
Coiltronics
CDRH3D16-4R7
CDRH3D16-100
LQH32CN4R7M23
LQH32CN4R7M33
LQH32CN4R7M53
LPO6610-472
LPO3310-472
SDRC10-4R7
4.7
10
0.90
0.55
0.45
0.65
0.65
1.10
0.80
1.53
1.30
0.98
1.77
0.11
0.21
0.20
0.15
0.15
0.20
0.27
0.117
0.122
0.122
0.082
3.8x3.8x1.8
3.8x3.8x1.8
2.5x3.2x2.0
2.5x3.2x2.0
2.5x3.2x1.55
5.5x6.6x1.0
3.3x3.3x1.0
4.5x3.6x1.0
5.7x4.4x1.0
3.1x3.1x1.85
5.2x5.2x1.8
Shielded
Shielded
Non-Shielded
Non-Shielded
Non-Shielded
1mm
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
1mm
1mm Shielded
1mm Shielded
Shielded
SDR10-4R7
SD3118-4R7
SD18-4R7
Shielded
Table 4: Typical Surface Mount Inductors.
Manufacturer
Part Number
Value
Voltage
Temp. Co.
Case
Murata
Murata
Murata
Murata
GRM21BR61A475KA73L
GRM18BR60J475KE19D
GRM21BR60J106KE19
GRM21BR60J226ME39
4.7μF
4.7μF
10μF
22μF
10V
6.3V
6.3V
6.3V
X5R
X5R
X5R
X5R
0805
0603
0805
0805
Table 5: Surface Mount Capacitors.
1. For reduced quiescent current R2 = 221k.
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DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
Ordering Information
Output Voltage1
Package
Marking2
Part Number (Tape and Reel)3
0.6
1.2
1.6
1.8
2.5
3.3
SC70JW-8
SC70JW-8
SC70JW-8
SC70JW-8
SC70JW-8
SC70JW-8
NUXYY
PBXYY
PYXYY
OKXYY
OYXYY
PLXYY
AAT1143IJS-0.6-T1
AAT1143IJS-1.2-T1
AAT1143IJS-1.6-T1
AAT1143IJS-1.8-T1
AAT1143IJS-2.5-T1
AAT1143IJS-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
SC70JW-8
0.50 BSC 0.50 BSC 0.50 BSC
0.225 0.075
2.00 0.20
0.048REF
0.100
0.45 0.10
4° 4°
7° 3°
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 generally held on part numbers listed in BOLD.
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DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
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