Skyworks CDRH8D28 2a step-down converter Datasheet

DATA SHEET
AAT1153
2A Step-Down Converter
General Description
Features
The AAT1153 SwitchReg™ is a 1.2MHz constant frequency current mode PWM step-down converter. It is
ideal for portable equipment requiring very high current
up to 2A from single-cell Lithium-ion batteries while still
achieving over 90% efficiency during peak load conditions. The AAT1153 also can run at 100% duty cycle for
low dropout operation, extending battery life in portable
systems while light load operation provides very low
output ripple for noise sensitive applications.
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The AAT1153 can supply up to 2A output load current
from a 2.5V to 5.5V input voltage and the output voltage
can be regulated as low as 0.6V. The high switching frequency minimizes the size of external components while
keeping switching losses low. The internal slope compensation setting allows the device to operate with smaller
inductor values to optimize size and provide efficient
operation.
The AAT1153 is available with adjustable (0.6V to VIN)
output voltage. The device is available in a Pb-free, 3mm
x 3mm 10-lead TDFN package and is rated over the
-40°C to +85°C temperature range.
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Input Voltage Range: 2.5V to 5.5V
Output Voltages from 0.6V to VIN
2A Output Current
High Efficiency: Up to 95%
1.2MHz Constant Switching Frequency
Low RDS(ON) Internal Switches: 0.15Ω
Allows Use of Ceramic Capacitors
Current Mode Operation for Excellent Line and Load
Transient Response
Short-Circuit and Thermal Fault Protection
Soft Start
Low Dropout Operation: 100% Duty Cycle
Low Shutdown Current: ISHUTDOWN < 1μA
TDFN33-10 Package
-40°C to +85°C Temperature Range
Applications
•
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•
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Cellular Phones
Digital Cameras
DSP Core Supplies
PDAs
Portable Instruments
Smart Phones
Typical Application
VIN 2.5V-5.5V
1
2
C1
22μF
3
EN
LX
IN
LX
AIN
6 AGND
4 AGND
AAT1153
FB
PGND
PGND
8
7
5
10
9
L1
2.2μH
R1
634kΩ
VOUT
1.8V, 2A
C2
22μF
R2
316kΩ
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201992B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
1
DATA SHEET
AAT1153
2A Step-Down Converter
Pin Descriptions
Pin #
Symbol
1
EN
2
3
4, 6
IN
AIN
AGND
5
FB
7, 8
9, 10
LX
PGND
EP
Function
Enable pin. Active high. In shutdown, all functions are disabled drawing <1μA supply current. Do not leave
EN floating.
Power supply input pin. Must be closely decoupled to AGND with a 2.2μF or greater ceramic capacitor.
Analog supply input pin. Provides bias for internal circuitry.
Analog ground pin
Feedback input. Connect FB to the center point of the external resistor divider. The feedback threshold
voltage is 0.6V.
Switching node pin. Connect the output inductor to this pin.
Power ground pin
Power ground exposed pad. Must be connected to bare copper ground plane.
Pin Configuration
TDFN-10
(Top View)
EN
1
10
PGND
IN
2
9
PGND
AIN
3
8
LX
AGND
4
7
LX
FB/OUT
5
6
AGND
1. FB pin for the adjustable voltage version (AAT1153IDE-0.6), OUT pin for the fixed voltage version (AAT1153IDE-1.8).
2
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DATA SHEET
AAT1153
2A Step-Down Converter
Absolute Maximum Ratings1
Symbol
Description
IN, AIN
VFB, VLX
VEN
PGND, AGND
TA
TSTORAGE
TLEAD
Input Supply Voltages
FB, LX Voltages
EN Voltage
Ground Voltages
Operating Temperature Range
Storage Temperature
Lead Temperature (Soldering, 10s)
Value
Units
-0.3 to 6.0
-0.3 to VIN + 0.3
-0.3 to VIN + 0.3
-0.3 to 6.0
-40 to +85
-65 to 150
300
V
V
V
V
°C
°C
°C
Value
Units
45
2.2
°C/W
W
Thermal Information2
Symbol
JA
PD
Description
Thermal Resistance3
Maximum Thermal Dissipation at TA = 25°C
1. Absolute Maximum Ratings are those values beyond which the life of a device may be impaired.
2. TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formula: TJ = TA + PD x JA.
3. Thermal Resistance is specified with approximately 1 square inch of 1 oz. copper.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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3
DATA SHEET
AAT1153
2A Step-Down Converter
Electrical Characteristics1
VIN = 3.6V, TA = -40°C to +85°C unless otherwise noted; typical values are TA = 25°C.
Symbol
VIN
VOUT
Description
IQ
Input DC Supply Current
IFB
Feedback Input Bias Current
VFB
Regulated Feedback Voltage3
VLINEREG/
VIN
VLOADREG/
IOUT
VFB
FOSC
TS
TSD
THYS
ILIM
RDS(ON)
VEN(L)
VEN(H)
IEN
Conditions
Input Voltage Range2
Output Voltage Range
Min
Typ
Max
Units
V
V
μA
μA
nA
0.6000
0.6000
0.6000
5.5
VIN
500
1
30
0.6120
0.6135
0.6150
0.20
%/V
2.5
0.6
Active Mode: VFB = 0.5V
Shutdown Mode: VEN = 0V, VAIN = 5.5V
VFB = 0.65V
TA = 25°C
0°C ≤ TA ≤ 85°C
-40°C ≤ TA ≤ 85°C
300
0.1
0.5880
0.5865
0.5850
Line Regulation
VIN = 2.5V to 5.5V, IOUT = 10mA
0.10
Load Regulation
IOUT = 10mA to 2000mA
0.20
Output Voltage Accuracy
Oscillator Frequency
Startup Time
Over-Temperature Shutdown Threshold
Over-Temperature Shutdown Hysteresis
Peak Switch Current
P-CH MOSFET
N-CH MOSFET
Enable Threshold Low
Enable Threshold High
Input Low Current
VIN = 2.5 to 5.5V, IOUT = 10 to 2000mA
VFB = 0.6V
From Enable to Output Regulation
-3
0.96
2.5
VIN = 3.6V
VIN = 3.6V
VIN = VEN = 5.5V
1.2
1.3
170
10
3.5
135
95
1.5
-1.0
V
%/A
+3
1.44
200
150
0.3
1.0
% VOUT
MHz
ms
°C
°C
A
mΩ
V
V
μA
1. The AAT1153 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. VIN should be not less than VOUT + VDROPOUT, where VDROPOUT = IOUT x (RDS(ON)PMOS + ESRINDUCTOR), typically VDROPOUT = 0.3V.
3. The regulated feedback voltage is tested in an internal test mode that connects VFB to the output of the error amplifier.
4
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DATA SHEET
AAT1153
2A Step-Down Converter
Typical Characteristics
Efficiency vs. Output Current
DC Regulation
(VOUT = 3.3V, TA = 25°C, L = 2.2µH, CIN = COUT = 22µF)
(VOUT = 3.3V, TA = 25°C, L = 2.2µH, CIN = COUT = 22µF)
100
VIN = 3.7V
70
Output Voltage (V)
80
Efficiency (%)
3.399
VIN = 4.2V
90
VIN = 5.5V
VIN = 5.0V
60
50
40
30
20
10
0
0.1
1
10
100
1000
3.366
VIN = 3.7V
3.267
VIN = 4.2V
3.234
0
200
400
Output Current (mA)
600
800
1000 1200 1400 1600 1800 2000
Output Current (mA)
Efficiency vs. Output Current
DC Regulation
(VOUT = 1.8V, TA = 25°C, L = 2.2µH, CIN = COUT = 22µF)
(VOUT = 1.8V, TA = 25°C, L = 2.2µH, CIN = COUT = 22µF)
100
1.854
80
70
60
VIN = 5.0V
50
Output Voltage (V)
VIN = 4.2V
VIN = 3.6V
VIN = 2.5V
90
Efficiency (%)
VIN = 5.0V
3.300
3.201
10000
VIN = 5.5V
3.333
VIN = 5.5V
40
30
20
1.836
VIN = 4.2V
1.818
VIN = 5.0V
VIN = 5.5V
1.800
1.782
VIN = 3.6V
1.764
VIN = 2.5V
10
0
0.1
1.746
1
10
100
1000
0
10000
200
400
Output Current (mA)
800
1000 1200 1400 1600 1800 2000
Output Current (mA)
Efficiency vs. Output Current
DC Regulation
(VOUT = 1.5V, TA = 25°C, L = 2.2µH, CIN = COUT = 22µF)
(VOUT = 1.5V, TA = 25°C, L = 2.2µH, CIN = COUT = 22µF)
100
1.545
90
70
60
VIN = 4.2V
Output Voltage (V)
80
Efficiency (%)
600
VIN = 3.6V
VIN = 2.5V
VIN = 5.5V
50
40
VIN = 5.0V
30
20
10
0
0.1
1
10
100
Output Current (mA)
1000
10000
1.530
VIN = 4.2V
1.515
VIN = 5.0V
VIN = 5.5V
1.500
1.485
VIN = 3.6V
VIN = 2.5V
1.470
1.455
0
200
400
600
800
1000 1200 1400 1600 1800 2000
Output Current (mA)
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5
DATA SHEET
AAT1153
2A Step-Down Converter
Typical Characteristics
Efficiency vs. Output Current
DC Regulation
(VOUT = 1.2V, TA = 25°C, L = 2.2µH, CIN = COUT = 22µF)
(VOUT = 1.2V, TA = 25°C, L = 2.2µH, CIN = COUT = 22µF)
100
1.236
Efficiency (%)
80
70
60
VIN = 3.6V
VIN = 4.2V
Output Voltage (V)
90
VIN = 2.5V
50
VIN = 5.5V
VIN = 5.0V
40
30
20
10
0
0.1
1
10
100
1000
1.224
1.212
VIN = 3.6V
VIN = 2.5V
1.188
1.176
200
400
600
Output Current (mA)
800
1000 1200 1400 1600 1800 2000
Output Current (mA)
Quiescent Current vs. Input Voltage
Quiescent Current vs. Temperature
(TA = 25°C, L = 2.2µH, CIN = COUT = 22µF)
(L = 2.2µH, CIN = COUT = 22µF)
0.38
Quiescent Current (µA)
400
0.36
Input Current (mA)
VIN = 5.5V
1.200
1.164
0
10000
VIN = 5.0V
VIN = 4.2V
VOUT = 3.3V
0.34
0.32
0.30
VOUT = 1.8V
0.28
0.26
0.24
0.22
0.20
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Input Voltage (V)
350
VIN = 4.2V
VOUT = 3.3V
300
VIN = 3.6V
VOUT = 1.8V
250
200
-40
-20
0
20
40
60
Temperature (°C)
Line Regulation
(VOUT = 1.8V, L = 2.2µH, CIN = COUT = 22µF)
Accuracy (%)
0.40
IOUT = 1A
IOUT = 600mA
0.20
IOUT = 1mA
IOUT = 1.5A
0.00
-0.20
-0.40
2.5
IOUT = 2A
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Input Voltage (V)
6
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80
100
DATA SHEET
AAT1153
2A Step-Down Converter
Typical Characteristics
P-Channel RDS(ON) vs. Input Voltage
N-Channel RDS(ON) vs. Input Voltage
200
150
85°C
160
25°C
140
120
-40°C
110
3.5
4
4.5
5
-40°C
50
2.5
80
3
25°C
90
70
100
2.5
85°C
130
RDS(ON)_N (mΩ
Ω)
RDS(ON)_P (mΩ
Ω)
180
5.5
3
3.5
4.5
5
5.5
Switching Frequency vs. Temperature
Reference Voltage vs. Temperature
(VIN = 3.6V; VOUT = 1.8V)
(VIN = 3.6V)
1.4
0.609
1.3
1.2
1.1
1.0
-40
-20
0
20
40
60
80
0.607
0.605
0.603
0.601
0.599
0.597
0.595
0.593
0.591
-40
100
-20
Temperature (°C)
0
20
40
60
80
100
Temperature (°C)
Soft Start
Load Transient Response
(VIN = 3.6V; VOUT = 1.8V; IOUT = 2A; CFF = 22pF)
(VIN = 3.6V; VOUT = 1.8V; L = 2.2µH; CIN = COUT = 22µF)
2
0
-2
1.4
1.0
0.6
0.2
Output Voltage (top) (V)
4
2.2
2.0
1.8
1.6
2A
200mA
-0.2
Time (400µs/div)
2.6
2.2
1.8
1.4
1.0
0.6
0.2
-0.2
Output Current (bottom) (A)
6
Input Current
(bottom) (A)
Enable Voltage (top) (V)
Output Voltage (middle) (V)
4
Input Voltage (V)
Reference Voltage (V)
Switching Frequency (MHz)
Input Voltage (V)
Time (400µs/div)
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DATA SHEET
AAT1153
2A Step-Down Converter
Typical Characteristics
Output Ripple
Output Ripple
(VIN = 3.6V; VOUT = 1.8V; IOUT = 0A; L = 2.2µH)
(VIN = 3.6V; VOUT = 1.8V; IOUT = 2A; L = 2.2µH)
1.79
0.3
0.2
0.1
0.0
-0.1
Time (100µs/div)
8
Output Voltage (top) (V)
Output Voltage (top) (V)
1.80
1.82
1.81
1.80
1.79
2.5
2.3
2.1
1.9
1.7
1.5
Time (400ns/div)
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Inductor Current (bottom) (A)
1.81
Inductor Current (bottom) (A)
1.82
DATA SHEET
AAT1153
2A Step-Down Converter
Functional Block Diagram
OSC
SLOPE
COMP
IN
VIN 2.5V to 5.5V
ISENSE
AMP
0.6V
Softstart
SET
I
COMP
RESET
PWM
LOGIC
NON-OVERLAP
CONTROL
LX
FB/OUT
R1*
R1*
0.65V
Over-Temperature
and Short-Circuit
Protection
COUT
OVDET
R2*
R2*
IZERO
COMP
0.6V
EN
VOUT
L1
REF
PGND
SHUTDOWN
AIN AGND
*The resistor divider R1 + R2 is internally set for the fixed output versions, and is externally set for the adjustable output versions.
Functional Description
The AAT1153 is a high output current monolithic switchmode step-down DC-DC converter. The device operates
at a fixed 1.2MHz switching frequency, and uses a slope
compensated current mode architecture. This step-down
DC-DC converter can supply up to 2A output current at
VIN = 3V and has an input voltage range from 2.5V to
5.5V. It minimizes external component size and optimizes efficiency at the heavy load range. The slope compensation allows the device to remain stable over a
wider range of inductor values so that smaller values
(1μH to 4.7μH) with lower DCR can be used to achieve
higher efficiency. Apart from the small bypass input
capacitor, only a small L-C filter is required at the output.
The device can be programmed with external feedback
to any voltage, ranging from 0.6V to near the input voltage. It uses internal MOSFETs to achieve high efficiency
and can generate very low output voltages by using an
internal reference of 0.6V. At dropout, the converter duty
cycle increases to 100% and the output voltage tracks
the input voltage minus the low RDS(ON) drop of the
P-channel high-side MOSFET and the inductor DCR. The
internal error amplifier and compensation provides
excellent transient response, load and line regulation.
Internal soft start eliminates any output voltage overshoot when the enable or the input voltage is applied.
Current Mode PWM Control
Slope compensated current mode PWM control provides
stable switching and cycle-by-cycle current limit for
excellent load and line response with protection of the
internal main switch (P-channel MOSFET) and synchronous rectifier (N-channel MOSFET). During normal
operation, the internal P-channel MOSFET is turned on
for a specified time to ramp the inductor current at each
rising edge of the internal oscillator, and switched off
when the peak inductor current is above the error voltage. The current comparator, ICOMP, limits the peak inductor current. When the main switch is off, the synchronous rectifier turns on immediately and stays on until
either the inductor current starts to reverse, as indicated
by the current reversal comparator, IZERO, or the beginning of the next clock cycle.
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9
DATA SHEET
AAT1153
2A Step-Down Converter
Control Loop
The AAT1153 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 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. The error amplifier
reference is fixed at 0.6V.
Soft Start / Enable
Soft start limits the current surge seen at the input and
eliminates output voltage overshoot. The enable pin is
active high. When pulled low, the enable input (EN)
forces the AAT1153 into a low-power, 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 3.5A. 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. The termination lasts for seven consecutive
clock cycles after a current limit has been sensed during
a series of four consecutive clock cycles.
10
Thermal protection completely disables switching when
internal dissipation becomes excessive. The junction
over-temperature threshold is 170°C with 10°C of hysteresis. Once an over-temperature or over-current fault
conditions is removed, the output voltage automatically
recovers.
Dropout Operation
When the battery input voltage decreases near the value
of the output voltage, the AAT1153 allows the main
switch to remain on for more than one switching cycle
and increases the duty cycle until it reaches 100%. The
duty cycle D of a step-down converter is defined as:
D = TON · FOSC · 100% ≈
VOUT
· 100%
VIN
Where TON is the main switch on time and FOSC is the
oscillator frequency. The output voltage then is the input
voltage minus the voltage drop across the main switch
and the inductor. At low input supply voltage, the RDS(ON)
of the P-channel MOSFET increases, and the efficiency of
the converter decreases. Caution must be exercised to
ensure the heat dissipated does not exceed the maximum junction temperature of the IC.
Maximum Load Current
The AAT1153 will operate with an input supply voltage
as low as 2.5V, however, the maximum load current
decreases at lower input voltages due to a large IR drop
on the main switch and synchronous rectifier. The slope
compensation signal reduces the peak inductor current
as a function of the duty cycle to prevent sub-harmonic
oscillations at duty cycles greater than 50%. Conversely,
the current limit increases as the duty cycle decreases.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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DATA SHEET
AAT1153
2A Step-Down Converter
Applications Information
VIN 2.5V-5.5V
1
2
C1
22μF
3
LX
EN
IN
LX
AIN
AAT1153-0.6
6 AGND
4 AGND
FB
PGND
PGND
8
L1
2.2μH
7
5
C3
22pF
10
9
VOUT
1.8V, 2A
R1
634kΩ
C2
22μF
R2
316kΩ
Figure 1: Basic Application Circuit.
Setting the Output Voltage
Figure 1 shows the basic application circuit for the
AAT1153. The AAT1153 can be externally programmed.
Resistors R1 and R2 in Figure 1 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 1
summarizes the resistor values for various output voltages with R2 set to either 59k for good noise immunity
or 316k for reduced no load input current.
The AAT1153, combined with an external feed forward
capacitor (C3 in Figure 1), delivers enhanced transient
response for extreme pulsed load applications. The addition of the feed forward capacitor typically requires a
larger output capacitor C2 for stability. The external
resistor sets the output voltage according to the following equation:
⎛
R1 ⎞
VOUT = 0.6V · 1 +
⎝
R2 ⎠
R1 =
⎛ VOUT ⎞
- 1 · R2
⎝ 0.6V ⎠
Table 1 shows the resistor selection for different output
voltage settings.
VOUT (V)
R2 = 59k
R1 (k)
R2 = 316k
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
105
158
210
261
316
365
422
475
634
655
732
1000
1430
Table 1: Resistor Selections for Different Output
Voltage Settings (Standard 1% Resistors
Substituted For Calculated Values).
Inductor Selection
For most designs, the AAT1153 operates with inductor
values of 1μH to 4.7μH. Low inductance values are
physically smaller but require faster switching, which
results in some efficiency loss. The inductor value can
be derived from the following equation:
L=
VOUT · (VIN - VOUT)
VIN · ΔIL · fOSC
Where IL is inductor ripple current. Large value inductors lower ripple current and small value inductors result
in high ripple currents. Choose inductor ripple current
approximately 30% of the maximum load current 2A, or
ΔIL = 600mA
For output voltages above 2.0V, when light-load efficiency is important, the minimum recommended inductor is 2.2μH.
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.
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DATA SHEET
AAT1153
2A Step-Down Converter
Always consider the losses associated with the DCR and
its effect on the total converter efficiency when selecting
an inductor. For optimum voltage-positioning load transients, choose an inductor with DC series resistance in
the 20m to 100m range. For higher efficiency at
heavy loads (above 200mA), or minimal load regulation
(but some transient overshoot), the resistance should be
kept below 100m. The DC current rating of the inductor should be at least equal to the maximum load current
plus half the ripple current to prevent core saturation (2A
+ 600mA). Table 2 lists some typical surface mount
inductors that meet target applications for the AAT1153.
For example, the 2.2μH CDRH5D16-2R2 inductor selected from Sumida has a 28.7mΩ DCR and a 3.0ADC current rating. At full load, the inductor DC loss is 57mW
which gives a 1.6% loss in efficiency for a 1200mA, 1.8V
output.
Slope Compensation
The AAT1153 step-down converter uses peak current
mode control with slope compensation for stability when
duty cycles are greater than 50%. The slope compensation is set to maintain stability with lower value inductors
which provide better overall efficiency. The output inductor value must be selected so the inductor current down
slope meets the internal slope compensation requirements. As an example, the value of the slope compensation is set to 1A/μs which is large enough to guarantee
stability when using a 2.2μH inductor for all output voltage levels from 0.6V to 3.3V.
The worst case external current slope (m) using the
2.2μH inductor is when VOUT = 3.3V and is:
m=
VOUT 3.3
=
= 1.5A/µs
L
2.2
To keep the power supply stable when the duty cycle is
above 50%, the internal slope compensation (mA)
should be:
ma ≥
1
· m = 0.75A/µs
2
Therefore, to guarantee current loop stability, the slope
of the compensation ramp must be greater than one-half
of the down slope of the current waveform. So the inter-
12
nal slope compensated value of 1A/μs will guarantee
stability using a 2.2μH inductor value for all output voltages from 0.6V to 3.3V.
Input Capacitor Selection
The input capacitor reduces the surge current drawn
from the input and switching noise from the device. The
input capacitor impedance at the switching frequency
should be less than the input source impedance to prevent high frequency switching current passing to the
input. The calculated value varies with input voltage and
is a maximum when VIN is double the output voltage.
CIN =
CIN(MIN) =
V ⎞
VO ⎛
· 1- O
VIN ⎝
VIN ⎠
⎛ VPP
⎞
- ESR · fS
⎝ IO
⎠
1
⎛ VPP
⎞
- ESR · 4 · fS
⎝ IO
⎠
A low ESR input capacitor sized for maximum RMS current must be used. Ceramic capacitors with X5R or X7R
dielectrics are highly recommended because of their low
ESR and small temperature coefficients. A 22μF ceramic capacitor for most applications is sufficient. A large
value may be used for improved input voltage filtering.
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.
IRMS(MAX) =
1
· IO
2
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 (C1) can be seen in the
evaluation board layout in Figures 2 and 3.
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DATA SHEET
AAT1153
2A 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 Selection
In many practical designs, to get the required ESR, a
capacitor with much more capacitance than is needed
must be selected.
For both continuous or discontinuous inductor current
mode operation, the ESR of the COUT needed to limit the
ripple to ∆VO, V peak-to-peak is:
ESR ≤
Ripple current flowing through a capacitor’s ESR causes
power dissipation in the capacitor. This power dissipation
causes a temperature increase internal to the capacitor.
Excessive temperature can seriously shorten the expected life of a capacitor. Capacitors have ripple current ratings that are dependent on ambient temperature and
should not be exceeded. The output capacitor ripple current is the inductor current, IL, minus the output current,
IO. The RMS value of the ripple current flowing in the
output capacitance (continuous inductor current mode
operation) is given by:
The function of output capacitance is to store energy to
attempt to maintain a constant voltage. The energy is
stored in the capacitor’s electric field due to the voltage
applied.
The value of output capacitance is generally selected to
limit output voltage ripple to the level required by the
specification. Since the ripple current in the output inductor is usually determined by L, VOUT and VIN, the series
impedance of the capacitor primarily determines the output voltage ripple. The three elements of the capacitor
that contribute to its impedance (and output voltage
ripple) are equivalent series resistance (ESR), equivalent
series inductance (ESL), and capacitance (C).
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 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 =
ΔVO
ΔIL
IRMS = ΔIL ·
3
= ΔIL · 0.289
6
ESL can be a problem by causing ringing in the low
megahertz region but can be controlled by choosing low
ESL capacitors, limiting lead length (PCB and capacitor),
and replacing one large device with several smaller ones
connected in parallel.
In conclusion, in order to meet the requirement of output voltage ripple small and regulation loop stability,
ceramic capacitors with X5R or X7R dielectrics are recommended due to their low ESR and high ripple current
ratings. The output ripple VOUT is determined by:
ΔVOUT ≤
1
VOUT · (VIN - VOUT) ⎛
⎞
· ⎝ESR +
8 · fOSC · COUT ⎠
VIN · fOSC · L
A 22μF ceramic capacitor can satisfy most applications.
3 · ΔILOAD
VDROOP · fS
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13
DATA SHEET
AAT1153
2A Step-Down Converter
Thermal Calculations
Layout Guidance
There are three types of losses associated with the
AAT1153 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:
When laying out the PC board, the following layout
guideline should be followed to ensure proper operation
of the AAT1153:
PTOTAL =
1.
2.
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.
3.
4.
5.
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
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 DFN-10 package which is
45°C/W.
TJ(MAX) = PTOTAL · ΘJA + TAMB
14
6.
7.
The exposed pad (EP) must be reliably soldered to
the GND plane. A PGND pad below EP is strongly
recommended.
The power traces, including the GND trace, the LX
trace and the IN trace should be kept short, direct
and wide to allow large current flow. The L1 connection to the LX pins should be as short as possible.
Use several VIA pads when routing between layers.
The input capacitor (C1) should connect as closely
as possible to IN (Pin 2) and AGND (Pins 4 and 6) to
get good power filtering.
Keep the switching node, LX (Pins 7 and 8) away
from the sensitive FB/OUT node.
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 FB pin
(Pin 5) to minimize the length of the high impedance
feedback trace.
The output capacitor C2 and L1 should be connected
as closely as possible. The connection of L1 to the LX
pin should be as short as possible and there should
not be any signal lines under the inductor.
The resistance of the trace from the load return to
PGND 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.
Figures 3, 4 and 5 show an example of a layout with 4
layers. The internal 2 layers are SGND and PGND.
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DATA SHEET
AAT1153
2A Step-Down Converter
Manufacturer
Part Number
Sumida
Sumida
Sumida
Coiltronics
Coiltronics
Coiltronics
Inductance
(μH)
Max DC
Current (A)
DCR (m)
2.2
3.3
4.7
2.0
3.3
4.7
3.0
2.6
3.4
3.3
2.6
2.1
28.7
35.6
19
23
29
39
CDRH5D16
CDRH8D28
SD53
Size LxWxH
(mm)
Type
5.8x5.8x1.8
Shielded
8.3x8.3x3.0
Shielded
5.2x5.2x3.0
Shielded
Manufacturer
Part Number
Value
Voltage (V)
Temp. Co.
Case
Murata
Murata
Murata
GRM219R60J106KE19
GRM21BR60J226ME39
GRM1551X1E220JZ01B
10μF
22μF
22pF
6.3
6.3
25
X5R
X5R
JIS
0805
0805
0402
Table 2: Suggested Component Selection Information.
JP1
SGND
U1
AAT1153
1
JP3
EN
PGND
IN
PGND
10
PGND
2.5V ~ 5.5V
VIN
2
3
C1
22μF
PGND
4
LX
AIN
LX
AGND
9
SGND
SW
8
L1
2.2μH
7
SGND
5
FB
AGND
EP
6
SGND
11
JP2
R2A 316k
R2B 634k
R2C 1M
R2D 1.43M
R1
316k
SGND
1
2
3
4
5
6
7
8
1.2V, 1.8V, 2.5V, 3.3V
VOUT
C2
22μF
C3
22pF
JP2_1-2:
JP2_3-4:
JP2_5-6:
JP2_7-8:
1.2V;
1.8V;
2.5V;
3.3V.
L1: CDRH5D16-2R2NC
C1, C2: GRM21BR60J226ME39
Figure 2: AAT1153 Recommended Evaluation Board Schematic.
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15
DATA SHEET
AAT1153
2A Step-Down Converter
Figure 4: AAT1153 Evaluation
Board Component Side Layout.
Figure 5: Exploded View of AAT1153
Evaluation Board Component Side Layout.
Figure 6: AAT1153 Evaluation
Board Solder Side Layout.
16
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DATA SHEET
AAT1153
2A Step-Down Converter
Step-Down Converter Design Example
Specifications
VO = 1.8V @ 2A
VIN = 2.7V to 4.2V (3.6V nominal)
fS = 1.2MHz
Transient droop = 200mV
∆VO = 50mV
1.8V Output Inductor
ΔIL = 30% ⋅ IO = 0.3 · 2 = 600mA
L=
VOUT · (VIN(MAX) - VOUT)
1.8 · (4.2 - 1.8)
=
= 1.4µH
VIN(MAX) ⋅ ΔIL ⋅ fOSC
4.2 ⋅ 0.6 · 1.2 · 106
For Sumida 2.2μH inductor (CDRH2D14) with DCR 75m, the ∆IL should be:
ΔIL =
VO ⎛ VO ⎞
⋅ 1· T = 395mA
L ⎝ VIN ⎠
IPKL = IO +
0.395
ΔIL
=2+
= 2.2A
2
2
PL = IO2 ⋅ DCR = 22 ⋅ 0.0287 = 114.8mW
1.8V Output Capacitor
COUT =
3 · ΔILOAD
3 · 1.2
=
= 25µF; use 22µF
0.2 · 1.2 · 106
VDROOP · fS
ESR ≤
0.05
ΔVO
=
= 0.13Ω
ΔIL
0.395
Select a 22μF, 10m ESR ceramic capacitor to meet the ripple 50mV requirement.
ΔVOUT ≤
=
1
VOUT · (VIN - VOUT) ⎛
⎞
· ⎝ESR +
8 · fOSC · COUT ⎠
VIN · fOSC · L
1.8 · (4.2 - 1.8)
1
⎛
⎞
· ⎝ 0.01 +
= 5.7mV
6
-6
6
-6 ⎠
4.2 · 1.2 · 10 · 2.2 · 10
8 · 1.2 · 10 · 22 · 10
IRMS = IL ·0.289 = 0.395 · 0.289 = 114mArms
PCOUT = ESR · IRMS2 = 0.01 · 12 = 10mW
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17
DATA SHEET
AAT1153
2A Step-Down Converter
Input Capacitor
Input ripple VPP = 25mV
CIN(MIN) =
IRMS =
1
⎛ VPP
⎞
- ESR · 4 · fS
⎝ IO
⎠
=
1
= 13.9µF; use 22µF
⎛ 0.025
⎞
- 0.01 · 4 · 1.2 · 106
⎝ 2
⎠
IO
2
=
= 1Arms
2
2
PCIN = ESR · IRMS2 = 0.01 · 12 = 10mW
AAT1153 Losses
PTOTAL = IO2 · RDS(ON)P · D + IO2 · RDS(ON)N · (1 - D) + (tSW · fS · IO) · VIN
= 22 · 0.135 ·
18
1.8
1.8⎞
⎛
+ 22 · 0.095 · 1 + (5 · 10-9 · 1.2 · 106 · 2) · 4.2 = 498.9mW
⎝
4.2
4.2⎠
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DATA SHEET
AAT1153
2A Step-Down Converter
Ordering Information
Output Voltage
Package
Marking1
Part Number (Tape and Reel)2
Adj. 0.6V to VIN
TDFN33-10
ZSXYY
AAT1153IDE-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 Information3
TDFN33-10
Pin 1 dot by marking
0.500 BSC
1.70 ± 0.05
3.00 ± 0.05
0.23 ± 0.05
Pin 1 identification
R0.200
0.40 ± 0.05
3.00 ± 0.05
2.40 ± 0.05
Top View
0.05 ± 0.05
0.203 REF
0.75 ± 0.05
Bottom View
Side View
All dimensions in millimeters.
1. XYY = assembly and date code.
2. Sample stock is generally held on all part numbers listed in BOLD.
3. The leadless package family, which includes QFN, TQFN, DFN, TDFN and STDFN, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing
process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection.
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