AAT1143_201983B.pdf

DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
General Description
Features
The AAT1143 SwitchReg™ is a 1MHz step-down converter 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
• Temperature Range: -40°C to +85°C
The AAT1143 is available in either a fixed version with
internal feedback or a programmable version with external feedback resistors. It can deliver 400mA of load current 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.
The AAT1143 is designed to maintain high efficiency
throughout the operating range, which is critical for portable applications.
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.
Applications
•
•
•
•
•
•
Cellular Phones
Digital Cameras
Handheld Instruments
Microprocessor / DSP Core / IO Power
PDAs and Handheld Computers
USB Devices
Typical Application (Fixed Output Voltage)
VO
U1
AAT1143
3
1
C2
4.7μF
5
8
(VOUT = 2.5V; VIN = 3.3V)
VIN
LX
EN
OUT
AGND
PGND
Efficiency vs. Load Current
PGND
PGND
4
2
7
6
100
L1
95
4.7μH
C1
4.7μF
Efficiency (%)
VIN
90
85
80
75
70
65
60
0.1
1
10
100
1000
Output Current (mA)
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201983B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 25, 2013
1
DATA SHEET
AAT1143
1MHz 400mA 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 highand low-side MOSFETs.
Non-power signal ground pin.
Main power ground return pin. 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
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
201983B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 25, 2013
DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
Absolute Maximum Ratings1
Symbol
Description
VIN
VLX
VOUT
VEN
TJ
TLEAD
Input Voltage 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 VP + 0.3
-0.3 to VP + 0.3
-0.3 to 6.0
-40 to 150
300
V
V
V
V
°C
°C
Value
Units
625
160
mW
°C/W
Thermal Information
Symbol
PD
JA
Description
Maximum Power Dissipation (SC70JW-8)
Thermal Resistance2 (SC70JW-8)
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.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
201983B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 25, 2013
3
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
Conditions
Step-Down Converter
Input Voltage
VIN
VUVLO
UVLO Threshold
VOUT
Output Voltage Tolerance
VOUT
Output Voltage Range
IQ
ISHDN
ILIM
RDS(ON)H
RDS(ON)L
ILXLEAK
VLinereg
VOUT
IOUT
ROUT
FOSC
TSD
THYS
EN
VEN(L)
VEN(H)
IEN
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
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
Fixed Output Version
Adjustable Output Version2
No Load, 0.6V Adjustable Version
EN = AGND = PGND
Max
Units
5.5
2.6
V
V
mV
V
%
100
1.8
-3.0
0.6
0.6
25
+3.0
4.0
2.5
50
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
597
250
0.7
600
1.0
140
15
1
0.2
615
0.2
1.5
0.6
VIN = VFB = 5.5V
1.4
-1.0
1.0
V
μA
μA
mA


μA
%/V
mV
μA
k
MHz
°C
°C
V
V
μA
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 correlation with statistical process controls.
2. For adjustable version with higher than 2.5V output, please consult your Skyworks representative.
4
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
201983B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 25, 2013
DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
Typical Characteristics
Efficiency vs. Load
Load Regulation
(VOUT = 2.5V; L = 4.7μ
μH)
(VOUT = 2.5V; L = 4.7μ
μH)
100
2.0
VIN = 3.3V
Output Error (%)
Efficiency (%)
VIN = 3.0V
90
VIN = 3.6V
80
70
1.0
VIN = 3.0V
0.0
VIN = 3.3V
-1.0
VIN = 3.6V
60
0.1
-2.0
1
10
100
1000
0.1
1
10
Output Current (mA)
DC Regulation
(VOUT = 1.8V; L = 4.7μ
μH)
(VOUT = 1.8V; L = 4.7μ
μH)
100
2.0
Output Error (%)
VIN = 3.6V
VIN = 2.7V
90
Efficiency (%)
1000
Output Current (mA)
Efficiency vs. Load
80
VIN = 4.2V
70
60
50
1.0
VIN = 4.2V
0.0
VIN = 2.7V
-1.0
VIN = 3.6V
-2.0
0.1
1
10
100
1000
0.1
1
10
Output Current (mA)
100
1000
Output Current (mA)
Frequency vs. Input Voltage
Output Voltage Error vs. Temperature
(VOUT = 1.8V)
(VIN = 3.6V; VO = 1.5V)
2.0
1.0
0.5
Output Error (%)
Frequency Variation (%)
100
0.0
-0.5
-1.0
-1.5
-2.0
1.0
0.0
-1.0
-2.0
2.7
3.1
3.5
3.9
4.3
Input Voltage (V)
4.7
5.1
5.5
-40
-20
0
20
40
60
80
100
Temperature (°°C)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
201983B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 25, 2013
5
DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
Typical Characteristics
Switching Frequency vs. Temperature
Quiescent Current vs. Input Voltage
(VIN = 3.6V; VO = 1.5V)
(VO = 1.8V)
35
Supply Current (μ
μA)
Variation (%)
0.20
0.10
0.00
-0.10
85°C
30
25°C
25
20
-40°C
-0.20
-40
15
-20
0
20
60
80
2.5
100
4.0
4.5
5.0
5.5
P-Channel RDS(ON) vs. Input Voltage
N-Channel RDS(ON) vs. Input Voltage
750
700
700
650
100°C
RDS(ON) (mΩ
Ω)
120°C
600
550
85°C
500
450
25°C
120°C
100°C
600
550
500
85°C
450
25°C
350
300
300
2.5
3.0
3.5
4.0
4.5
5.0
5.5
2.5
6.0
Input Voltage (V)
3.0
3.5
4.0
4.5
5.0
5.5
Load Transient Response
(30mA to 300mA; VIN = 3.6V; VOUT = 1.8V;
C1 = 10μ
μF; C4 = 100pF; see Figure 1)
1.9
1.2
1.7
1.0
1.6
300mA
0.8
30mA
0.6
1.5
0.4
1.4
0.2
1.3
0.0
1.2
-0.2
Time (25μs/div)
1.4
0.1
0.0
-0.1
-0.2
1.2
300mA
1.0
30mA
0.8
-0.3
0.6
-0.4
0.4
-0.5
0.2
-0.6
0.0
-0.7
-0.2
Time (25μs/div)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
201983B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 25, 2013
Load and Inductor Current
(200mA/div) (bottom)
1.4
Load and Inductor Current
(200mA/div) (bottom)
2.0
Output Voltage (AC Coupled)
(top) (V)
Load Transient Response
1.8
6.0
Input Voltage (V)
(30mA to 300mA; VIN = 3.6V; VOUT = 1.8V; C1 = 10μ
μF)
Output Voltage
(top) (V)
6.0
400
350
6
3.5
Input Voltage (V)
750
400
3.0
Temperature (°°C)
650
RDS(ON) (mΩ
Ω)
40
DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
Typical Characteristics
Line Transient
(VOUT = 1.8V @ 400mA)
1.2
1.0
1.8
300mA
1.7
1.6
0.8
0.6
30mA
1.5
0.4
1.4
0.2
1.3
0.0
1.2
-0.2
1.90
7.0
1.85
6.5
1.80
6.0
1.75
5.5
1.70
5.0
1.65
4.5
1.60
4.0
1.55
3.5
1.50
3.0
Time (25μ
μs/div)
Time (25μs/div)
Line Regulation
Soft Start
(VOUT = 1.8V)
(VIN = 3.6V; VOUT = 1.8V; 400mA)
IOUT = 100mA
Accuracy (%)
0
-0.05
-0.1
IOUT = 10mA
-0.15
-0.2
IOUT = 400mA
-0.25
-0.3
-0.35
2.5
3.0
3.5
4.0
4.5
Input Voltage (V)
5.0
5.5
4.0
3.5
3.0
3.0
2.0
2.5
1.0
2.0
0.0
1.5
-1.0
1.0
-2.0
0.5
-3.0
0.0
-4.0
-0.5
Inductor Current
(bottom) (A)
Enable and Output Voltage
(top) (V)
0.1
0.05
Input Voltage
(bottom) (V)
Output Voltage
(top) (V)
1.9
Load and Inductor Current
(200mA/div) (bottom)
1.4
2.0
Output Voltage
(top) (V)
Load Transient Response
(30mA to 300mA; VIN = 3.6V; VOUT = 1.8V; C1 = 4.7μ
μF)
6.0
Time (250μ
μs/div)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
201983B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 25, 2013
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DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
Functional Block Diagram
VIN
OUT
See note
Err
Amp
.
DH
Voltage
Reference
LX
Logic
DL
EN
INPUT
PGND
AGND
Note: For adjustable version, the internal feedback divider is omitted and the FB pin is tied directly
to the internal error amplifier.
Functional Description
The AAT1143 is a high performance 400mA 1MHz monolithic step-down converter. It has been designed with the
goal of minimizing external component size and optimizing 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).
The fixed output version requires only three external
power components (CIN, COUT, and L). The adjustable version can be programmed with external feedback to any
voltage, ranging from 0.6V to the input voltage. An addi-
8
tional feed-forward capacitor can also be added 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 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 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
201983B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 25, 2013
DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
1
2
3
Enable
VIN
C4
100pF
U1
AAT1143
1
VOUT =1.8V
R1
2
118k
3
L1
C1
10μF
4
EN
PGND
OUT PGND
VIN
PGND
LX
AGND
8
7
6
5
4.7μH
R2
59k
C2
4.7μF
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.
Control Loop
The AAT1143 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 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 voltage is internally set to program the converter output
voltage. For the adjustable output, the error amplifier
reference is fixed at 0.6V.
non-switching state. The total input current during shutdown is less than 1μA.
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.
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 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.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
201983B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 25, 2013
9
DATA SHEET
AAT1143
1MHz 400mA 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 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.
0.75 ⋅ VO 0.75 ⋅ 1.5V
A
=
= 0.24
L
4.7μH
μsec
m=
This is the internal slope compensation for the adjustable (0.6V) version or low-voltage fixed versions. 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
Input Capacitor
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.
CIN =
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 105mW 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.
⎛ VPP
⎞
- ESR · FS
⎝ IO
⎠
VO ⎛
V ⎞
1
· 1 - O = for VIN = 2 · VO
4
VIN ⎝
VIN ⎠
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
0.6V Adjustable
With External
Resistive Divider
In this case, a standard 10μH value is selected.
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.
V ⎞
VO ⎛
· 1- O
VIN ⎝
VIN ⎠
Fixed Output
Output
Voltage
0.6V to
2.0V
2.5V
0.6V to
2.0V
2.5V to
3.3V
Inductor
Slope
Compensation
4.7μH
0.24A/μsec
10μH
0.24A/μsec
4.7μH
0.24A/μsec
4.7μH
0.48A/μsec
Table 1: Inductor Values.
The maximum input capacitor RMS current is:
IRMS = IO ·
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
10
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201983B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 25, 2013
1
2
DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
L=
⎛ V ⎞
VOUT
1.5V
⎛ 1.5V⎞
⋅ 1 - OUT =
⋅ 1= 4.82μH
IO ⋅ k ⋅ F ⎝
VIN ⎠ 0.4A ⋅ 0.4 ⋅ 1.25MHz ⎝ 4.2V⎠
VO
⎛
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.
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.
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 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) =
1
2· 3
·
VOUT · (VIN(MAX) - VOUT)
L · FS · VIN(MAX)
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
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.
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 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
12
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 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
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
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
75
113
150
187
221
261
301
332
442
464
523
715
Thermal Calculations
There are three types of losses associated with the
AAT1143 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:
PTOTAL =
Table 2: Adjustable Resistor Values For Use With
0.6V Step-Down Converter.
IO2 · (RDS(ON)H · VO + RDS(ON)L · [VIN - VO])
VIN
+ (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 converter switching losses.
1
2
3
Enable
VIN
C4
100pF
U1
AAT1143
1
VOUT =1.8V
R1
L1
4.7μH
C1
10μF
C3
n/a
2
118k
3
4
R2
59k
EN
PGND
OUT
PGND
VIN
PGND
LX
AGND
8
7
6
5
C2
4.7μF
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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13
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:
PTOTAL = IO2 · RDS(ON)H + IQ · VIN
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.
Given the total losses, the maximum junction temperature can be derived from the JA for the SC70JW-8 package which is 160°C/W.
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.
1.
2.
3.
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.
14
4.
The input capacitor (C2) should connect as closely as
possible to VIN (Pin 3) and PGND (Pins 6 through 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. 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 impedance feedback trace.
The resistance of the trace from the load return to
PGND (Pins 6 through 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.
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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
L1 = 3
μsec
μsec
⋅ VO2 = 3
⋅ 1.8V = 5.4μH (see Table 1)
A
A
For Sumida inductor CDRH3D16, 4.7μH, DCR = 105mΩ.
⎛ 1.8V⎞
VO
1.8V
⎛ V ⎞
⋅ 1- O =
⋅ 1-⎝
= 218mA
L1 ⋅ FS ⎝ VIN ⎠ 4.7μH ⋅ 1.0MHz
4.2V⎠
ΔIL1 =
IPKL1 = IO +
ΔIL1
= 0.4A + 0.11A = 0.51A
2
PL1 = IO2 ⋅ DCR = 0.4A2 ⋅ 105mΩ = 17mW
1.8V Output Capacitor
VDROOP = 0.2V
COUT =
3 · ΔILOAD
3 · 0.3A
=
= 4.5μF
VDROOP · FS
0.2V · 1MHz
IRMS =
(VO) · (VIN(MAX) - VO)
1
1.8V · (4.2V - 1.8V)
·
= 63mArms
=
L1 · FS · VIN(MAX)
2 · 3 4.7μH · 1.0MHz · 4.2V
2· 3
1
·
Pesr = esr · IRMS2 = 5mΩ · (63mA)2 = 20μW
Input Capacitor
Input Ripple VPP = 25mV
CIN =
IRMS =
⎛ VPP
⎝ IO
1
1
=
= 4.75μF
⎞
⎛ 25mV
⎞
- 5mΩ · 4 · 1MHz
- ESR · 4 · FS
⎠
⎝ 0.4A
⎠
IO
= 0.2Arms
2
P = esr · IRMS2 = 5mΩ · (0.2A)2 = 0.2mW
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15
DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
AAT1143 Losses
PTOTAL =
IO2 · (RDS(ON)H · VO + RDS(ON)L · [VIN -VO])
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
16
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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
124
137
187
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
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.
Manufacturer
Part Number
Inductance
(μH)
Max DC
Current (A)
DCR ()
Size (mm)
LxWxH
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
SDR10-4R7
SD3118-4R7
SD18-4R7
4.7
10
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
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
1mm
1mm Shielded
1mm Shielded
Shielded
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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17
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
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 generally held on part numbers listed in BOLD.
18
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DATA SHEET
AAT1143
1MHz 400mA Step-Down Converter
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