SKYWORKS AAT1126

DATA SHEET
AAT1126
600mA, 1MHz Step-Down Converter
General Description
Features
The AAT1126 SwitchReg™ is a member of Skyworks'
Total Power Management IC (TPMIC™) product family. It
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 AAT1126 the ideal choice for portable applications.
• VIN Range: 2.7V to 5.5V
• VOUT Adjustable Down to 0.6V
▪ Fixed or Adjustable Version
• Fast Turn-On Time (100μs Typical)
• 25μA No Load Quiescent Current
• Up to 97% Efficiency
• Output Current Up to 600mA
• 1MHz Switching Frequency
• Soft Start
• Over-Temperature Protection
• Current Limit Protection
• 100% Duty Cycle Low-Dropout Operation
• 0.1μA Shutdown Current
• SOT23-5 Package
• Temperature Range: -40°C to +85°C
The AAT1126 is available in either a fixed version with
internal feedback or a programmable version with external feedback resistors. It can deliver up to 600mA 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 AAT1126 feedback and control delivers
excellent load regulation and transient response with a
small output inductor and capacitor.
The AAT1126 is designed to maintain high efficiency
throughout the operating range and provides fast turnon time.
The AAT1126 is available in a Pb-free, space-saving
SOT23-5 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
VIN
U1
AAT1126
5
C2
4.7µF
2
1
VIN
LX
3
L1
4.7µH
EN
GND
OUT
4
C1
10µF
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201976B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013
1
DATA SHEET
AAT1126
600mA, 1MHz Step-Down Converter
Pin Descriptions
Pin #
Symbol
1
2
GND
EN
3
LX
4
OUT
5
VIN
Function
Ground pin.
Enable pin.
Switching node. Connect the inductor to this pin. It is internally connected to the drain of both highand low-side MOSFETs.
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.
Pin Configuration
SOT23-5
(Top View)
2
GND
1
EN
2
LX
3
5
VIN
4
OUT
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DATA SHEET
AAT1126
600mA, 1MHz Step-Down Converter
Absolute Maximum Ratings1
Symbol
VIN
VLX
VOUT
VEN
TJ
TLEAD
Description
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 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
667
150
mW
°C/W
Thermal Information
Symbol
PD
JA
Description
Maximum Power Dissipation (SOT23-5)
Thermal Resistance2 (SOT23-5)
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
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3
DATA SHEET
AAT1126
600mA, 1MHz 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
Min
Typ
Max
Units
5.5
2.6
V
V
mV
V
%
V
μA
μA
mA


μA
%/V
mV
μA
k
μs
MHz
°C
°C
Step-Down Converter
VIN
VUVLO
VOUT
VOUT
IQ
ISHDN
IOUT_X
RDS(ON)H
RDS(ON)L
ILXLEAK
VLinereg
VOUT
IOUT
ROUT
TS
FOSC
TSD
THYS
EN
VEN(L)
VEN(H)
IEN
Input Voltage
UVLO Threshold
Output Voltage Tolerance
Output Voltage Range
Quiescent Current
Shutdown Current
Maximum Load Current
High Side Switch On Resistance
Low Side Switch On Resistance
LX Leakage Current
Line Regulation
Out Threshold Voltage Accuracy
Out Leakage Current
Out Impedance
Start-Up Time
Oscillator Frequency
Over-Temperature Shutdown Threshold
Over-Temperature Shutdown Hysteresis
Enable Threshold Low
Enable Threshold High
Input Low Current
2.7
VIN Rising
Hysteresis
VIN Falling
IOUT = 0 to 600mA, VIN = 2.7V to 5.5V
100
1.8
-3.5
0.6
No Load, 0.6V Adjustable Version
EN = AGND = PGND
25
+3.5
VIN
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
From Enable to Output Regulation
TA = 25°C
591
600
1
0.5
609
0.2
250
0.7
100
1.0
140
15
1.5
0.6
VIN = VFB = 5.5V
1.4
-1.0
1.0
V
V
μA
1. The AAT1126 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
201976B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013
DATA SHEET
AAT1126
600mA, 1MHz Step-Down Converter
Typical Characteristics
Efficiency vs. Load
DC Regulation
(VOUT = 3.3V; L = 10μ
μH)
(VOUT = 3.3V; L = 10μ
μH)
3.0
90
Output Error (%)
Efficiency (%)
100
VIN = 3.9V
VIN = 4.2V
80
70
2.0
VIN = 4.2V
1.0
0.0
-1.0
VIN = 3.9V
-2.0
-3.0
60
0.1
1
10
100
0.1
1000
1
10
Output Current (mA)
100
1000
100
1000
DC Regulation
(VOUT = 2.5V; L = 10μ
μH)
(VOUT = 2.5V; L = 10μ
μH)
3.0
100
Output Error (%)
VIN = 3.3V
Efficiency (%)
1000
Output Current (mA)
Efficiency vs. Load
90
VIN = 3.0V
VIN = 3.6V
80
70
VIN = 3.3V
2.0
VIN = 3.6V
1.0
0.0
VIN = 3.0V
-1.0
-2.0
-3.0
60
0.1
1
10
100
1000
0.1
1
Output Current (mA)
10
Output Current (mA)
Efficiency vs. Load
DC Regulation
(VOUT = 1.5V; L = 4.7μ
μH)
(VOUT = 1.5V; L = 4.7μ
μH)
3.0
100
VIN = 2.7V
VIN = 3.6V
Output Error (%)
90
Efficiency (%)
100
80
VIN = 4.2V
70
60
50
VIN = 4.2V
2.0
VIN = 3.6V
1.0
0.0
VIN = 2.7V
-1.0
-2.0
-3.0
0.1
1
10
Output Current (mA)
100
1000
0.1
1
10
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
AAT1126
600mA, 1MHz Step-Down Converter
Typical Characteristics
Frequency vs. Input Voltage
Output Voltage Error vs. Temperature
(VIN = 3.6V; VO = 2.5V)
1.0
2.0
0.5
1.5
Output Error (%)
Frequency Variation (%)
(VOUT = 1.8V)
0.0
-0.5
-1.0
-1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
2.7
3.1
3.5
3.9
4.3
4.7
5.1
-2.0
-40
5.5
-20
0
20
60
80
100
Temperature (°°C)
Input Voltage (V)
Switching Frequency vs. Temperature
Quiescent Current vs. Input Voltage
(VIN = 3.6V; VO = 1.5V)
(VO = 1.8V)
0.20
35
Supply Current (μ
μA)
Variation (%)
40
0.10
0.00
-0.10
85°C
30
25°C
25
20
-40°C
-0.20
-40
15
-20
0
20
40
60
80
2.5
100
4.0
4.5
5.0
5.5
Input Voltage (V)
P-Channel RDS(ON) vs. Input Voltage
N-Channel RDS(ON) vs. Input Voltage
6.0
750
700
700
650
120°C
650
100°C
RDS(ON) (mΩ
Ω)
RDS(ON) (mΩ
Ω)
3.5
Temperature (°°C)
750
600
550
85°C
500
450
25°C
400
120°C
100°C
600
550
500
85°C
450
400
25°C
350
350
300
300
2.5
3.0
3.5
4.0
4.5
Input Voltage (V)
6
3.0
5.0
5.5
6.0
2.5
3.0
3.5
4.0
4.5
5.0
Input Voltage (V)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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5.5
6.0
DATA SHEET
AAT1126
600mA, 1MHz Step-Down Converter
Typical Characteristics
Load Transient Response
Load Transient Response
(30mA - 300mA; VIN = 3.6V; VOUT = 2.5V; C1 = 22μ
μF)
1.3
1.1
300mA
30mA
0.9
0.7
0.5
0.3
0.1
-0.1
2.65
1.5
2.55
Output Voltage
(top) (V)
1.5
1.3
1.1
300mA
2.45
0.9
30mA
2.35
0.7
2.25
0.5
0.3
2.15
0.1
2.05
-0.1
Time (25μs/div)
Load and Inductor Current
(200mA/div) (bottom)
1.65
1.60
1.55
1.50
1.45
1.40
1.35
1.30
1.25
1.20
1.15
1.10
1.05
1.00
Load and Inductor Current
(200mA/div) (bottom)
Output Voltage
(top) (V)
(30mA - 300mA; VIN = 3.6V; VOUT = 1.5V; C1 = 22μ
μF)
Time (25μs/div)
Line Transient
Line Regulation
(VOUT = 2.5V @ 500mA)
(VOUT = 1.5V)
2.55
6.5
2.50
6.0
2.45
5.5
2.40
5.0
2.35
4.5
2.30
2.25
4.0
2.20
3.5
2.15
3.0
1.5
Accuracy (%)
7.0
Input Voltage
(bottom) (V)
Output Voltage
(top) (V)
2
2.60
IOUT = 600mA
1
0.5
IOUT = 100mA
0
IOUT = 10mA
-0.5
-1
2.5
Time (25μ
μs/div)
Output Ripple
4
4.5
5
5.5
6
Soft Start
(VIN = 3.6V; VOUT = 1.5V; L = 4.7μ
μH)
0.8
0
0.7
-20
0.6
-40
0.5
-60
0.4
-80
0.3
-100
0.2
-120
0.1
Enable and Output Voltage
(top) (V)
0.9
20
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)
40
Inductor Current
(bottom) (A)
Output Voltage (AC Coupled)
(top) (mV)
3.5
Input Voltage (V)
(VIN = 3.6V; VOUT = 1.8V; 400mA)
Time (250ns/div)
3
Time (50μs/div)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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7
DATA SHEET
AAT1126
600mA, 1MHz Step-Down Converter
Functional Block Diagram
VIN
OUT
See note
Err
Amp
.
DH
Voltage
Reference
LX
Logic
DL
EN
INPUT
GND
Note: For adjustable version, the internal feedback divider is omitted and the OUT pin is tied directly
to the internal error amplifier.
Functional Description
The AAT1126 is a high performance 600mA 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
10μF 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 heavy load.
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
201976B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013
DATA SHEET
AAT1126
600mA, 1MHz Step-Down Converter
JP1
VIN
1
2
3
1
Enable
L1
4.7μH
VOUT = 1.8V
2
3
GND
VIN
EN
OUT
LX
AAT1126
C1
10μF
5
4
C2
4.7μF
C4
100pF
R1
118K
U1 AAT1126 SOT23-5
L1 CDRH3D16-4R7
C1 10μF 10V 0805 X5R
C2 4.7μF 10V 0805 X5R
C3
n/a
R2
59K
GND
LX
Figure 1: Enhanced Transient Response Schematic.
Control Loop
The AAT1126 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.
down is less than 1μA. The AAT1126 provides turn-on
within 100μs (typical) of the enable input transition.
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 AAT1126 into a low-power,
non-switching state. The total input current during shut-
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
201976B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013
9
DATA SHEET
AAT1126
600mA, 1MHz 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 AAT1126 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
µs
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
µs
0.75 ⋅ VO
≈ 3 A ⋅ VO
=
m
A
0.24A µs
=3
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 =
For high-voltage fixed versions (2.5V and above), m =
0.48A/μs. Table 1 displays inductor values for the
AAT1126 fixed and adjustable options.
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.
⎛ 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.
µs
⋅ 2.5V = 7.5µH
A
In this case, a standard 10μH value is selected.
V ⎞
VO ⎛
· 1- O
VIN ⎝
VIN ⎠
Configuration
0.6V Adjustable
With External
Resistive Divider
Fixed Output
Output
Voltage
0.6V to
2.0V
2.5V to
3.3V
0.6V to
2.0V
2.5V to
3.3V
Slope
Compensation
4.7μH
0.24A/μs
10μH
0.24A/μs
4.7μH
0.24A/μs
4.7μH
0.48A/μs
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 ⎠
10
Inductor
D · (1 - D) =
0.52 =
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1
2
DATA SHEET
AAT1126
600mA, 1MHz Step-Down Converter
for VIN = 2 · VO
IRMS(MAX) =
VO
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.
Figure 2: AAT1126 Evaluation Board
Top Side.
The input capacitor provides a low impedance loop for
the edges of pulsed current drawn by the AAT1126. 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 3: Exploded View of Evaluation
Board Top Side Layout.
Figure 4: AAT1126 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
AAT1126
600mA, 1MHz Step-Down Converter
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 22μF X5R or
X7R ceramic capacitor 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 equa-
12
tion establishes a limit on the minimum value for the
output capacitor with respect to load transients.
The internal voltage loop compensation limits the minimum output capacitor value to 10μF. 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 · F · 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.
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
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 AAT1126, 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
AAT1126
600mA, 1MHz Step-Down Converter
JP1
VIN
1
2
3
Enable
1
L1
4.7μH
2
3
VOUT
R1
118K
GND
VIN
EN
OUT
5
4
C2
4.7μF
LX
AAT1126
C1
10μF
U1 AAT1126 SOT23-5
L1 CDRH3D16-4R7
C2 4.7μF 10V 0805 X5R
C1 10μF 6.3V 0805 X5R
R2
59K
GND
LX
Figure 5: AAT1126 Adjustable Evaluation Board Schematic.
VOUT (V)
R2 = 59k
R1 (k)
R2 = 221k
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
PTOTAL =
IO2 · (RDSON(HS) · VO + RDSON(LS) · [VIN - VO])
VIN
+ (tsw · F · 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 · RDSON(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 SOT23-5 package which is 150°C/W.
There are three types of losses associated with the
AAT1126 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:
TJ(MAX) = PTOTAL · ΘJA + TAMB
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13
DATA SHEET
AAT1126
600mA, 1MHz Step-Down Converter
Layout
3.
The suggested PCB layout for the AAT1126 is shown in
Figures 2, 3, and 4. The following guidelines should be
used to help ensure a proper layout.
1.
2.
14
The input capacitor (C2) should connect as closely as
possible to VIN (Pin 3) and GND (Pin 1).
C1 and L1 should be connected as closely as possible. The connection of L1 to the LX pin should be as
short as possible.
4.
The feedback trace or OUT pin (Pin 4) 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 4) to minimize the length of the high impedance feedback trace.
The resistance of the trace from the load return to
GND (Pin 1) should be kept to a minimum. This will
help to minimize any error in DC regulation due to
differences in the potential of the load return and the
AAT1126 ground.
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DATA SHEET
AAT1126
600mA, 1MHz Step-Down Converter
Step-Down Converter Design Example
Specifications
VO
VIN
FS
TAMB
= 1.8V @ 400mA (adjustable using 0.6V version), Pulsed Load ILOAD = 300mA
= 2.7V to 4.2V (3.6V nominal)
= 1.0MHz
= 85°C
1.8V Output Inductor
L1 = 3
μsec
μsec
⋅ VO2 = 3
⋅ 1.8V = 5.4μH
A
A
(see Table 1)
For Sumida inductor CDRH3D16, 4.7μH, DCR = 105m.
ΔIL1 =
⎛ 1.8V⎞
VO
V ⎞
1.8V
⎛
⋅ 1- O =
⋅ 1- ⎝
= 218mA
L1 ⋅ F ⎝
VIN ⎠ 4.7μH ⋅ 1.0MHz
4.2V⎠
IPKL1 = IO +
ΔIL1
= 0.4A + 0.11A = 0.51A
2
PL1 = IO2 ⋅ DCR = 0.4A2 ⋅ 105mΩ = 17mW
1.8V Output Capacitor
VDROOP = 0.05V
COUT =
3 · ΔILOAD
3 · 0.3A
=
= 18.0μF
VDROOP · FS
0.05V · 1MHz
IRMS =
(VO) · (VIN(MAX) - VO)
1
1.8V · (4.2V - 1.8V)
·
= 63mArms
=
L1 · F · VIN(MAX)
2 · 3 4.7μH · 1.0MHz · 4.2V
2· 3
1
·
Pesr = esr · IRMS2 = 5mΩ · (63mA)2 = 20μW
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15
DATA SHEET
AAT1126
600mA, 1MHz Step-Down Converter
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
AAT1126 Losses
PTOTAL =
IO2 · (RDSON(HS) · VO + RDSON(LS) · [VIN -VO])
VIN
+ (tsw · F · IO + IQ) · VIN
=
0.42 · (0.45Ω · 1.8V + 0.4Ω · [4.2V - 1.8V])
4.2V
+ (5ns · 1.0MHz · 0.4A + 50μA) · 4.2V = 76mW
TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (150°C/W) · 76mW = 96.4°C
16
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DATA SHEET
AAT1126
600mA, 1MHz Step-Down Converter
VOUT (V)
Adjustable Version (0.6V device)
R1 (k)
R2 = 59k
R1 (k)
R2 = 221k1
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
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
10
VOUT (V)
Fixed Version
R1 (k)
R2 Not Used
0.6-3.3V
L1 (μH)
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
Coilcraft
Coilcraft
Coiltronics
Coiltronics
Coiltronics
Coiltronics
CDRH3D16-4R7
CDRH3D16/HP-100
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
0.90
0.84
0.65
0.65
1.10
0.80
1.53
1.30
0.98
1.77
0.11
0.23
0.15
0.15
0.20
0.27
0.117
0.122
0.122
0.082
4.0x4.0x1.8
4.0x4.0x1.8
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
1mm
1mm
1mm Shielded
1mm Shielded
Shielded
Shielded
Table 4: Typical Surface Mount Inductors.
Manufacturer
Part Number
Value
Voltage
Temp. Co.
Case
Murata
Murata
GRM21BR60J226ME39
GRM21BR60J106KE19
22μF
10μF
6.3V
6.3V
X5R
X5R
0805
0805
Table 5: Surface Mount Capacitors.
1. For reduced quiescent current R2 = 221k.
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17
DATA SHEET
AAT1126
600mA, 1MHz Step-Down Converter
Ordering Information
Output Voltage1
Package
Marking2
Part Number (Tape and Reel)3
Adj. 0.6
SOT23-5
QPXYY
AAT1126IGV-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
SOT23-5
2.85 ± 0.15
1.90 BSC
0.075 ± 0.075
10°° ± 5°°
0.40 ± 0.10
0.15 ± 0.07
GAUGE PLANE
4°° ± 4°°
1.10 ± 0.20
0.60 REF
1.20 ± 0.25
2.80 ± 0.20
1.575 ± 0.125
0.95
BSC
0.60 REF
0.45 ± 0.15
0.10 BSC
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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