AAT1112 - Skyworks Solutions, Inc.

DATA SHEET
AAT1112
1.5A, 1.4MHz Step-Down Converter
General Description
Features
The AAT1112 SwitchReg is a 1.5A step-down converter
with an input voltage range of 2.4V to 5.5V and an
adjustable output voltage from 0.6V to VIN. The 1.4MHz
switching frequency enables the use of small external
components. The small footprint and high efficiency make
the AAT1112 an ideal choice for portable applications.
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The AAT1112 delivers 1.5A maximum output current
while consuming only 42μA of no-load quiescent current.
Ultra-low RDS(ON) integrated MOSFETs and 100% duty
cycle operation make the AAT1112 an ideal choice for
high output voltage, high current applications which
require a low dropout threshold.
The AAT1112 provides excellent transient response and
high output accuracy across the operating range. No
external compensation components are required.
The AAT1112 is designed to maintain high efficiency
throughout the load range. Pulling the MODE/ SYNC pin
high enables “PWM Only” mode, maintaining constant
frequency and low output ripple across the operating
range. Alternatively, the converter may be synchronized
to an external clock input via the MODE/SYNC pin. Overtemperature and short-circuit protection safeguard the
AAT1112 and system components from damage.
1.5A Maximum Output Current
Input Voltage: 2.4V to 5.5V
Output Voltage: 0.6V to VIN
Up to 95% Efficiency
42μA No Load Quiescent Current
No External Compensation Required
1.4MHz Switching Frequency
Synchronizable to External Clock
Optional “PWM Only” Low Noise Mode
100% Duty Cycle Low-Dropout Operation
Internal Soft Start
Over-Temperature and Current Limit Protection
<1μA Shutdown Current
TSOPJW-12 or TDFN33-12 Package
Temperature Range: -40°C to +85°C
Applications
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Cellular Phones
Digital Cameras
Hard Disk Drives
MP3 Players
PDAs and Handheld Computers
Portable Media Players
USB Devices
The AAT1112 is available in a Pb-free, space-saving
TDFN33-12 or 2.85 x 3mm TSOPJW-12 package. The
product is rated over an operating temperature range of
-40°C to +85°C.
Typical Application
L1
3.3μH
VIN
VP
LX
AAT1112
R1
267kΩ
VIN
C2
10μF
EN
C1
22μF
FB
MODE/SYNC
GND
VOUT = 3.3V
PGND
R2
59kΩ
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013
1
DATA SHEET
AAT1112
1.5A, 1.4MHz Step-Down Converter
Pin Descriptions
Pin #
TSOPJW-12
TDFN33-12
Symbol
Function
1
12
LX
2
3
11
10
VP
N/C
4
9
MODE/SYNC
5
8
EN
6
7
VIN
7
6
FB
8, 9, 10, 11
12
N/A
4, 5
1, 2, 3
EP
GND
PGND
Switching node. Connect the output inductor to this pin. The switching node is internally connected to the drain of both high- and low-side MOSFETs.
Input voltage for the power switches.
Not connected.
Connect to ground for PFM/PWM mode and optimized efficiency throughout the load
range. Connect high for low noise PWM operation under all operating conditions.
Connect to an external clock for synchronization (PWM only).
Enable pin. A logic low disables the converter and it consumes less than 1μA of current. When connected high, it resumes normal operation.
Power supply. Supplies power for the internal circuitry.
Feedback input pin. This pin is connected either directly to the converter output or
to an external resistive divider for an adjustable output.
Non-power signal ground pin.
Main power ground return pin. Connect to the output and input capacitor return.
Exposed paddle (bottom); connect to ground as closely as possible to the device.
Pin Configuration
TSOPJW-12
(Top View)
LX
1
12
PGND
VP
2
11
GND
N/C
3
10
GND
MODE/SYNC
4
9
GND
EN
5
8
GND
7
FB
VIN
2
TDFN33-12
(Top View)
6
PGND
1
12
LX
PGND
2
11
VP
PGND
3
10
N/C
GND
4
9
MODE/SYNC
GND
5
8
EN
FB
6
7
VIN
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013
DATA SHEET
AAT1112
1.5A, 1.4MHz Step-Down Converter
Absolute Maximum Ratings1
Symbol
Description
VIN
VLX
VFB
VN
TJ
TLEAD
VIN, VP to GND
LX Pin to GND
FB Pin to GND
MODE/SYNC, 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
Thermal Information
Symbol
Description
PD
Maximum Power Dissipation
JA
Thermal Resistance2
Value
TSOPJW-12
TDFN33-12
TSOPJW-12
TDFN33-12
0.625
2.0
160
50
Units
W
°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.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013
3
DATA SHEET
AAT1112
1.5A, 1.4MHz Step-Down Converter
Electrical Characteristics1
VIN = 3.6V; TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C.
Symbol
Description
VIN
VOUT
Input Voltage
Output Voltage Range
VUVLO
UVLO Threshold
VOUT
IQ
ISHDN
ILIM
RDS(ON)H
RDS(ON)L
ILXLEAK
ILXLK, R
VLOADREG
VLINEREG/
VIN
VFB
IFB
FOSC
TS
TSD
THYS
Output Voltage Tolerance
Quiescent Current
Shutdown Current
Current Limit
High Side Switch On-Resistance
Low Side Switch On-Resistance
LX Leakage Current
LX Reverse Leakage Current
Load Regulation
Line Regulation
Feedback Threshold Voltage Accuracy
(Adjustable Version)
FB Leakage Current
Internal Oscillator Frequency
Synchronous Clock
Start-Up Time
Over-Temperature Shutdown Threshold
Over-Temperature Shutdown Threshold
Conditions
Min
Typ
2.4
0.6
Max
Units
5.5
VIN
2.4
VIN = 5.5V, VLX = 0 to VIN
VIN Unconnected, VLX = 5.5V, VEN = GND
ILOAD = 0A to 1.5A
0.5
V
V
V
mV
V
%
μA
μA
A


μA
μA
%
VIN = 2.4V to 5.5V
0.2
%/V
VIN Rising
Hysteresis
VIN Falling
IOUT = 0A to 1.5A, VIN = 2.4V to 5.5V
No Load
VEN = GND
250
1.8
-3.0
42
3.0
90
1.0
1.8
0.120
0.085
No Load, TA = 25°C
1.0
1.0
0.591
0.60
0.609
V
1.4
0.2
1.68
3.0
μA
1.12
0.60
VOUT = 1.0V
From Enable to Output Regulation
150
140
15
MHz
μs
°C
°C
EN
VIL
Enable
VIH
Enable
IEN
Enable
MODE/SYNC
VMODE/SYNC(L) Enable
VMODE/SYNC(H) Enable
IMODE/SYNC
Enable
Threshold Low
Threshold High
Leakage Current
Threshold Low
Threshold High
Leakage Current
0.6
VIN = VEN = 5.5V
1.4
-1.0
VIN = VEN = 5.5V
1.4
-1.0
1.0
0.6
1.0
V
V
μA
V
V
μA
1. The AAT1112 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
201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013
DATA SHEET
AAT1112
1.5A, 1.4MHz Step-Down Converter
Typical Characteristics
Efficiency (%)
90
Load Regulation
(PFM Mode; VOUT = 3.3V)
(PFM Mode; VOUT = 3.3V)
0.50
VIN = 3.6V
80
VIN = 4.2V
VOUT Error (%)
100
Efficiency vs. Output Current
VIN = 5.0V
70
60
0.25
VIN = 3.6V
VIN = 4.2V
0.00
-0.25
VIN = 5.0V
50
40
0.1
1
10
100
1000
-0.50
0.1
10000
1
Output Current (mA)
10
100
1000
10000
1000
10000
1000
10000
Output Current (mA)
Efficiency vs. Output Current
Load Regulation
(PWM Mode; VOUT = 3.3V)
(PWM Mode; VOUT = 3.3V)
100
0.50
VIN = 3.6V
VOUT Error (%)
Efficiency (%)
80
VIN = 5.0V
60
VIN = 4.2V
40
20
0
1.0
10
100
1000
0.25
0.00
VIN = 4.2V
-0.25
-0.50
0.1
10000
1
Output Current (mA)
100
Load Regulation
(PFM Mode; VOUT = 2.5V)
(PFM Mode; VOUT = 2.5V)
0.50
80
VIN = 3.6V
VOUT Error (%)
Efficiency (%)
100
Efficiency vs. Output Current
VIN = 2.7V
VIN = 4.2V
70
60
0.1
10
Output Current (mA)
90
50
VIN = 5.0V
VIN = 3.6V
1
10
100
Output Current (mA)
1000
10000
VIN = 2.7V
0.25
VIN = 3.6V
0.00
VIN = 4.2V
-0.25
-0.50
0.1
1
10
100
Output Current (mA)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013
5
DATA SHEET
AAT1112
1.5A, 1.4MHz Step-Down Converter
Typical Characteristics
Efficiency vs. Output Current
Load Regulation
(PWM Mode; VOUT = 2.5V)
(PWM Mode; VOUT = 2.5V)
0.50
100
90
VOUT Error (%)
Efficiency (%)
VIN = 3.6V
VIN = 2.7V
80
70
60
VIN = 5.0V
50
40
30
VIN = 4.2V
20
10
0
VIN = 3.6V
1
10
100
1000
0.25
VIN = 5.0V
0.00
VIN = 4.2V
-0.25
-0.50
0.1
10000
VIN = 2.7V
1
10
1000
10000
Output Current (mA)
Output Current (mA)
Efficiency vs. Output Current
Load Regulation
(PFM Mode; VOUT = 1.8V)
(PFM Mode; VOUT = 1.8V)
100
0.50
VOUT Error (%)
VIN = 2.7V
90
Efficiency (%)
100
80
70
VIN = 4.2V
VIN = 3.6V
60
0.25
VIN = 2.7V
VIN = 3.6V
0.00
-0.25
50
VIN = 4.2V
40
0.1
1
10
100
1000
-0.50
0.1
10000
1
Output Current (mA)
10
100
1000
Output Current (mA)
Efficiency vs. Output Current
Load Regulation
(PWM Mode; VOUT = 1.8V)
(PWM Mode; VOUT = 1.8V)
100
0.50
90
Efficiency (%)
70
VOUT Error (%)
VIN = 2.7V
80
VIN = 4.2V
60
50
40
VIN = 3.6V
30
20
VIN = 2.7V
0.25
VIN = 3.6V
0.00
VIN = 4.2V
-0.25
10
0
1
10
100
Output Current (mA)
6
1000
10000
-0.50
0.1
1
10
100
1000
Output Current (mA)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013
10000
DATA SHEET
AAT1112
1.5A, 1.4MHz Step-Down Converter
Typical Characteristics
Efficiency vs. Output Current
Load Regulation
(PFM Mode; VOUT = 1.2V)
(PFM Mode; VOUT = 1.2V)
100
0.50
VIN = 2.7V
80
70
VIN = 4.2V
VIN = 3.6V
60
VOUT Error (%)
Efficiency (%)
90
50
VIN = 2.7V
0.25
VIN = 3.6V
0.00
VIN = 4.2V
-0.25
40
30
0.1
1
10
100
1000
-0.50
0.1
10000
1
Output Current (mA)
10
100
1000
10000
Output Current (mA)
Efficiency vs. Output Current
Load Regulation
(PWM Mode; VOUT = 1.2V)
(PWM Mode; VOUT = 1.2V)
100
0.50
90
Efficiency (%)
70
VOUT Error (%)
VIN = 2.7V
80
VIN = 4.2V
60
VIN = 3.6V
50
40
30
20
VIN = 2.7V
0.25
VIN = 3.6V
0.00
VIN = 4.2V
-0.25
10
0
1
10
100
1000
-0.50
10000
0.1
1
10000
Supply Current vs. Supply Voltage
(VIN = 3.6V; VOUT = 1.8V; IOUT = 1A)
(VOUT = 1.8V; No Load; PFM Mode)
70
0.8
65
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-40
1000
Output Voltage vs. Temperature
1.0
-1.0
100
Output Current (mA)
Supply Current (µA)
Output Voltage Change (%)
Output Current (mA)
10
-20
0
20
40
Temperature (°°C)
60
80
60
25°C
85°C
55
50
45
40
35
30
-40°C
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Supply Voltage (V)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013
7
DATA SHEET
AAT1112
1.5A, 1.4MHz Step-Down Converter
Switching Frequency vs. Temperature
Line Regulation
(VIN = 3.6V; VOUT = 1.8V; IOUT = 1A)
(VOUT = 1.8V; IOUT = 1A)
0.12
1.40
Output Voltage Error (%)
Switching Frequency (MHz)
Typical Characteristics
1.38
1.36
1.34
1.32
1.30
1.28
1.26
1.24
-40
-20
0
20
40
60
80
0.10
0.08
0.06
0.04
0.02
0.00
-0.02
-0.04
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
Switching Frequency (MHz)
Temperature (°°C)
Supply Voltage (V)
Switching Frequency vs. Input Voltage
Enable Soft Start
(IOUT = 1A)
(VOUT = 3.6V; IOUT = 1.5A)
1.40
1.39
1.38
EN
(2V/div)
VOUT = 1.8V VOUT = 2.5V
1.37
VOUT
(1V/div)
1.36
1.35
VOUT = 3.3V
1.34
IIN
(500mA/div)
1.33
1.32
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
Time (100µs/div)
Input Voltage (V)
P-Channel RDS(ON) vs. Input Voltage
N-Channel RDS(ON) vs. Input Voltage
180
170
150
120°C
140
130
RDS(ON) (mΩ
Ω)
RDS(ON) (mΩ
Ω)
160
150
140
85°C
130
120
110
25°C
110
100
85°C
90
80
70
90
60
Input Voltage (V)
8
120
100
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
120°C
25°C
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
Input Voltage (V)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013
DATA SHEET
AAT1112
1.5A, 1.4MHz Step-Down Converter
Light Load Switching Waveform
(PWM Mode; VIN = 3.6V; VOUT = 1.8V; 1mA Load)
2.6
2.0
2.4
0.0
2.2
-2.0
2.0
-4.0
1.8
-6.0
1.6
-8.0
1.4
-10.0
1.2
-12.0
1.0
4.0
1200
2.0
1000
0.0
800
-2.0
600
-4.0
400
-6.0
200
-8.0
0
-10.0
-200
-12.0
-400
Time (2.5µs/div)
Load Transient Response
(VIN = 3.6V; VOUT = 1.8V; CFF = 100pF)
700
4.0
600
0.0
500
-4.0
400
-8.0
300
-12.0
200
-16.0
100
-20.0
0
-24.0
-100
2.0
2.4
1.9
2.2
1.8
2.0
1.7
1.8
1.6
1.6
1.5
1.4
1.4
1.2
1.3
1.0
1.2
0.8
Time (20µs/div)
Load Transient Response
Line Transient Response
(VIN = 3.6V; VOUT = 1.8V; No CFF)
(VOUT = 1.8V; 1.5A Load)
5.0
3.0
3.0
4.5
2.8
1.5
2.5
4.0
2.6
1.0
2.0
3.5
2.4
0.5
1.5
3.0
2.2
0.0
1.0
2.5
2.0
-0.5
0.5
2.0
1.8
-1.0
0.0
1.5
1.6
-1.5
-0.5
1.0
1.4
Time (50µs/div)
Input Voltage
(top) (V)
3.5
2.0
Output Voltage
(bottom) (V)
2.5
Load Current
(bottom) (A)
Output Voltage
(top) (V)
Time (100µs/div)
Load Current
(bottom) (A)
8.0
Output Voltage
(top) (V)
Light Load Switching Waveform
(PFM Mode; VIN = 3.6V; VOUT = 1.8V; 1mA Load)
Inductor Ripple Current
(bottom) (mA)
Output Voltage (AC coupled)
(top) (mV)
Time (2.5µs/div)
Inductor Ripple Current
(bottom) (mA)
4.0
Output Voltage (AC coupled)
(top) (mV)
Heavy Load Switching Waveform
(PWM Mode; VIN = 3.6V; VOUT = 1.8V; 1.5A Load)
Inductor Ripple Current
(bottom) (mA)
Output Voltage (AC coupled)
(top) (mV)
Typical Characteristics
Time (200µs/div)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013
9
DATA SHEET
AAT1112
1.5A, 1.4MHz Step-Down Converter
Functional Block Diagram
FB
VP
VIN
Err.
Amp
DH
VREF
LX
Logic
EN
Input
DL
MODE/SYNC
PGND
GND
Functional Description
The AAT1112 is a high performance 1.5A monolithic
step-down converter operating at 1.4MHz switching frequency. It minimizes external component size and optimizes 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 3.3μH inductor and a 22μF ceramic capacitor are recommended for
a 3.3V output (see table of recommended values).
At dropout, the converter duty cycle increases to 100%
and the output voltage tracks the input voltage minus
the RDS(ON) drop of the P-channel high-side MOSFET (plus
the DC drop of the external inductor). The device integrates extremely low RDS(ON) MOSFETs to achieve low
dropout voltage during 100% duty cycle operation. This
is advantageous in applications requiring high output
voltages (typically > 2.5V) at low input voltages.
The integrated low-loss MOSFET switches can provide
greater than 95% efficiency at full load. PFM operation
10
maintains high efficiency under light load conditions
(typically <150mA). The MODE/ SYNC pin allows optional “PWM only” mode. This maintains constant frequency
and low output ripple across all load conditions.
Alternatively, the IC can be synchronized to an external
clock via the MODE/ SYNC input. External synchronization is maintained between 0.6MHz and 3.0MHz.
In battery-powered applications, as VIN decreases, the
converter dynamically adjusts the operating frequency
prior to dropout to maintain the required duty cycle and
provide accurate output regulation. Output regulation is
maintained until the dropout voltage, or minimum input
voltage, is reached. At 1.5A output load, dropout voltage headroom is approximately 200mV.
The AAT1112 typically achieves better than ±0.5% output regulation across the input voltage and output load
range. A current limit of 2.0A (typical) protects the IC
and system components from short-circuit damage.
Typical no load quiescent current is 42μA.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013
DATA SHEET
AAT1112
1.5A, 1.4MHz Step-Down Converter
Soft Start/Enable
Thermal protection completely disables switching when
the maximum junction temperature is detected. The
junction over-temperature threshold is 140°C with 15°C
of hysteresis. Once an over-temperature or over-current
fault condition is removed, the output voltage automatically recovers.
Soft start limits the current surge seen at the input and
eliminates output voltage overshoot. When pulled low,
the enable input forces the AAT1112 into a low-power,
non-switching state. The total input current during shutdown is less than 1μA.
Peak current mode control and optimized internal compensation provide high loop bandwidth and excellent
response to input voltage and fast load transient events.
Soft start eliminates output voltage overshoot when the
enable or the input voltage is applied. Under-voltage
lockout prevents spurious start-up events.
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.
Control Loop
The AAT1112 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 shortcircuit 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.
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.
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
reference voltage is internally set to program the converter output voltage greater than or equal to 0.6V.
Under-Voltage Lockout
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.
VIN
U1
AAT1112
TDFN33-12
C1
10μF
11
7
3
2
1
8
9
Enable
10
5
3
2
1
VP
VCC
EN
LX
N/C
FB
SYNC PGND
N/C
PGND
GND
PGND
3.3V
12
L1
3.3μH
4
C3
(optional)
R2
6
C2
22μF
3
2
R3
59K
1
SYNC
Figure 1: AAT1112 Schematic.
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DATA SHEET
AAT1112
1.5A, 1.4MHz Step-Down Converter
Component Selection
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 inductor should be set equal to the output voltage
numeric value in μH. This guarantees that there is sufficient internal slope compensation.
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 3.3μH CDRH4D28 series Sumida inductor has a
49.2m worst case DCR and a 1.57A DC current rating.
At full 1.5A load, the inductor DC loss is 97mW which
gives less than 1.5% loss in efficiency for a 1.5A, 3.3V
output.
Input Capacitor
Select a 10μF to 22μF 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 =
V ⎞
VO ⎛
· 1- O
VIN ⎝
VIN ⎠
⎛ VPP
⎞
- ESR · FS
⎝ IO
⎠
VO ⎛
V ⎞ 1
· 1 - O = for VIN = 2 · VO
VIN ⎝ VIN ⎠ 4
CIN(MIN) =
12
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.
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 =
1
2
for VIN = 2 · VO
IRMS(MAX) =
VO
IO
2
⎛
V ⎞
· 1- O
The term V ⎝ V ⎠ 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.
IN
IN
The input capacitor provides a low impedance loop for
the edges of pulsed current drawn by the AAT1112. 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 (C1) can be
seen in the evaluation board layout in the Layout section
of this datasheet (see 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
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DATA SHEET
AAT1112
1.5A, 1.4MHz Step-Down Converter
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 capacitor. 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 10μF to
22μF 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:
3 · ΔILOAD
COUT =
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 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.
Adjustable Output Resistor Selection
The output voltage on the AAT1112 is programmed with
external resistors R1 and R2. 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 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
221k for reduced no load input current.
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
3.0
3.3
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
237
267
75
113
150
187
221
261
301
332
442
464
523
715
887
1000
Table 1: AAT1112 Resistor Values for Various
Output Voltages.
Thermal Calculations
There are three types of losses associated with the
AAT1112 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 =
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.
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DATA SHEET
AAT1112
1.5A, 1.4MHz 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 TDFN3-12 and
TSOPJW-12 packages, which is 50°C/W and 160°C/W
respectively.
Layout
The suggested PCB layout for the AAT1112 is shown in
Figures 2 and 3. The following guidelines should be used
to help ensure a proper layout.
1.
2.
3.
4.
TJ(MAX) = PTOTAL · ΘJA + TAMB
5.
The input capacitor (C1) should connect as closely as
possible to VP and PGND.
C2 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 FB pin 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.
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.
Connect unused signal pins to ground to avoid
unwanted noise coupling.
Figure 2: AAT1112 Evaluation Board Top Side Layout.
14
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DATA SHEET
AAT1112
1.5A, 1.4MHz Step-Down Converter
Figure 3: AAT1112 Evaluation Board Bottom Side Layout.
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DATA SHEET
AAT1112
1.5A, 1.4MHz Step-Down Converter
Design Example
Specifications
VO 3.3V @ 1.5A, Pulsed Load ILOAD = 1.5A
VIN 2.7V to 4.2V (3.6V nominal)
FS 1.2MHz
TAMB 85°C in TDFN33-12 Package
Output Inductor
L1 = VO(μH) = 3.3μH; see Table 2.
For Sumida inductor CDRH4D28 3.3μH DCR = 49.2m max.
⎛
VO
V ⎞
3.3V
3.3V ⎞
⎛
⋅ 1 - O1 =
⋅ 1= 179mA
L1 ⋅ FS ⎝
VIN ⎠ 3.3µH ⋅ 1.2MHz ⎝
4.2V ⎠
ΔI1 =
IPK1 = IO1 +
ΔI1
= 1.5A + 0.089A = 1.59A
2
PL1 = IO12 ⋅ DCR = 1.5A2 ⋅ 49.2mΩ = 110mW
Output Capacitor
VDROOP = 0.2V
COUT =
3 · ΔILOAD
3 · 1.5A
=
= 18.8µF; use 22µF
VDROOP · FS
0.2V · 1.2MHz
IRMS(MAX) =
(VOUT) · (VIN(MAX) - VOUT)
1
3.3V · (4.2V - 3.3V)
·
= 52mArms
=
3.3µH
· 1.2MHz · 4.2V
·
V
L
·
F
·
2
3
2· 3
S
IN(MAX)
1
·
Pesr = esr · IRMS2 = 5mΩ · (52mA)2 = 13.3µW
Input Capacitor
Input Ripple VPP = 50mV
CIN =
1
⎛ VPP
⎞
- ESR · 4 · FS
⎝ IO1 + IO2
⎠
IRMS(MAX) =
=
1
= 7.3µF; use 10µF
⎛ 50mV
⎞
- 5mΩ · 4 · 1.2MHz
⎝ 1.5A
⎠
IO
= 0.75Arms
2
P = esr · IRMS2 = 5mΩ · (0.75A)2 = 3mW
16
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DATA SHEET
AAT1112
1.5A, 1.4MHz Step-Down Converter
AAT1112 Losses
Total losses can be estimated by calculating the dropout (VIN = VO) losses where the power MOSFET RDS(ON) will be at
the maximum value. All values assume an 85°C ambient temperature and a 120°C junction temperature with the TDFN
50°C/W package.
PLOSS = IO12 · RDS(ON)H = 1.5A2 · 0.16Ω = 0.36W
TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (50°C/W) · 360mW = 103°C
The total losses are also investigated at the nominal lithium-ion battery voltage (3.6V). The simplified version of the
RDS(ON) losses assumes that the N-channel and P-channel RDS(ON) are equal.
PTOTAL = IO2 · RDS(ON) + (tsw · FS · IO + IQ) · VIN
= 1.5A2 · 152mΩ + (5ns · 1.2MHz · 1.5A + 50μA) · 3.6V = 375mW
TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (50°C/W) · 375mW = 104°C
VOUT (V)
Inductance
(μH)
Part
Number
Manufacturer
Size (mm)
3.3
2.5
1.8
1.5
1.2
1.0
0.8
0.6
3.3
2.2
1.8
1.8
1.2
1.0
1.0
1.0
CDRH4D28
CDRH4D28
CDRH4D28
CDRH4D28
CDRH4D28
SD3114-1.0
SD3114-1.0
SD3114-1.0
Sumida
Sumida
Sumida
Sumida
Sumida
Cooper
Cooper
Cooper
5x5x3
5x5x3
5x5x3
5x5x3
5x5x3
3.1x3.1x1.45
3.1x3.1x1.45
3.1x3.1x1.45
Rated
Current
(A)
IRMS
(A)
ISAT
(A)
DCR ()
2.07
2.07
2.07
36.4
23.2
20.4
20.4
17.5
0.042
0.042
0.042
1.57
2.04
2.2
2.2
2.56
1.67
1.67
1.67
Table 2: Surface Mount Inductors.
Manufacturer
Part Number
Value
Voltage
Temp. Co.
Case
Murata
Murata
GRM21BR60J106KE19
GRM21BR60J226ME39
10μF
22μF
6.3V
6.3V
X5R
X5R
0805
0805
Table 3: Surface Mount Capacitors.
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DATA SHEET
AAT1112
1.5A, 1.4MHz Step-Down Converter
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
TSOPJW-12
TDFN33-12
YVXYY
SBXYY
AAT1112ITP-0.6-T1
AAT1112IWP-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
TSOPJW-12
2.85 ± 0.20
2.40 ± 0.10
0.20 + 0.10
- 0.05
0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC
7° NOM
0.04 REF
0.055 ± 0.045
0.15 ± 0.05
+ 0.10
1.00 - 0.065
0.9625 ± 0.0375
3.00 ± 0.10
4° ± 4°
0.45 ± 0.15
0.010
2.75 ± 0.25
All dimensions in millimeters.
1. XYY = assembly and date code.
2. Sample stock is generally held on 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.
18
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DATA SHEET
AAT1112
1.5A, 1.4MHz Step-Down Converter
TDFN33-12
Index Area
0.43 ± 0.05
0.1 REF
C0.3
0.45 ± 0.05
2.40 ± 0.05
3.00 ± 0.05
Detail "A"
3.00 ± 0.05
1.70 ± 0.05
Top View
Bottom View
0.23 ± 0.05
Pin 1 Indicator
(optional)
0.05 ± 0.05
0.23 ± 0.05
0.75 ± 0.05
Detail "A"
Side View
All dimensions in millimeters.
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