AAT1142
DATA SHEET
800mA Voltage-Scaling Step-Down Converter
1
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201931B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 17, 2012
General Description
The AAT1142 SwitchReg is a dynamically programmable
2.2MHz step-down converter with an input voltage range
of 2.7V to 5.5V and output from 0.6V to 2.0V. Its low
supply current, high level of integration, and small foot-
print make the AAT1142 the ideal choice for micropro-
cessor core power in systems such as smartphones.
The 2.2MHz switching frequency allows the use of a
small external inductor and capacitors. Peak current
mode control and internal compensation provide stable
operation and fast voltage response without over/under-
shoot or ringing.
The AAT1142 delivers up to 800mA of output current
while consuming 35μA of typical no load quiescent cur-
rent. Dynamic Voltage Management is provided through
I2C or Skyworks' S2Cwire™ (Simple Serial Control™)
single wire interface. The user can program the output
from 0.6V to 2.0V in 50mV steps.
The AAT1142 optimizes power efficiency throughout the
load range via PWM/PFM mode. Pulling the MODE/SYNC
pin high enables PWM Only mode, maintaining constant
frequency and low noise across the operating range.
Alternatively, the converter may be synchronized to an
external clock input via the MODE/SYNC pin. Over-
temperature and short-circuit protection safeguard the
AAT1142 and system components from damage.
The AAT1142 is available in a Pb-free, low-profile
3x3x0.8mm TDFN33-12 package. The device is rated
over the -40°C to +85°C temperature range.
Features
V
IN Range: 2.7V to 5.5V
V
OUT Programmable Range: 0.6V to 2.0V
Dynamic Voltage Management:
50mV Output Resolution
Fast, Stable Response
Serial Control Options:
I
2C Two-Wire Interface
S
2Cwire Single-Wire Interface
800mA Output Current
Up to 93% Efficiency
Line, Load Regulation Less Than ±0.5%
2.2MHz Switching Frequency
Ultra-Small External Filter
Low 35μA No Load Quiescent Current
100% Duty Cycle Low Dropout Operation
Internal Soft Start
Over-Temperature Protection
Current Limit Protection
Multi-Function MODE/SYNC Pin:
PFM/PWM for High Efficiency
PWM Only for Low Noise
Clock Input to Synchronize to System Clock
TDFN33-12 Package
Temperature Range: -40°C to +85°C
Applications
Camcorders
Cellular Phones and Smartphones
Digital Still Cameras
Handheld Instruments
Microprocessor / DSP Core
MP3, Portable Music, and Portable Media Players
PDAs and Handheld Computers
Typical Application
LXPVIN, VIN
AAT1142
MODE/SYNC
PGND
FB
L1
2.2μH
AGND
C2
4.7μF
C1
10μF
VIN: 2.7V to 5.5V
VOUT: 0.6V to 2.0V
800mA Maximum
SDA
SCL
EN/SET
I2C
S2Cwire*
*Optional S2Cwire or I2C Input
Efficiency vs. Load
(VOUT = 1.8V)
Output Current (mA)
Efficiency (%)
30
40
50
60
70
80
90
100
0 1 10 100 1000
PWM Only
Mode
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
VIN = 5.0V
AAT1142
DATA SHEET
800mA Voltage-Scaling Step-Down Converter
2Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201931B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 17, 2012
Pin Descriptions
Pin Number Symbol Function
12 LX Connect the output inductor to this pin. The switching node is internally connected to
the drain of both high- and low-side MOSFETs.
11 PGND Main power ground return pin. Connect to the output and input capacitor return.
10 MODE/SYNC
Connect to ground for PFM/PWM mode and optimized ef ciency throughout the load
range. Connect to high for low noise PWM Only operation under all operating condi-
tions. Connect to an external clock for synchronization (PWM Only).
9 SDA I2C control pin: Data input.
8 SCL I2C control pin: Clock input.
7 EN/SET I2C enable pin. Pull high to enable the AAT1142; pull low to disable the AAT1142.
Also serves as S2Cwire input for programmable output voltages.
6FB
Feedback input pin. This pin is connected directly to the converter output for pro-
grammable output.
4, 5 AGND Ground connection pin.
3 VIN Input voltage for the converter.
1 PVIN Input voltage for the power switches.
2 N/C Not connected.
EP Exposed paddle (bottom); connect to ground as closely as possible to the device.
Pin Configuration
TDFN33-12
(Top View)
PVIN
N/C
VIN
1
A
GND
AGND
FB
LX
PGND
MODE/SYNC
SDA
SCL
EN/SET
2
3
4
5
6
12
11
10
9
8
7
AAT1142
DATA SHEET
800mA Voltage-Scaling Step-Down Converter
3
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201931B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 17, 2012
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.
3. Derate 20mW/°C above 25°C.
Absolute Maximum Ratings1
Symbol Description Value Units
VIN, PVIN Input Voltage and Input Power to GND 6.0
V
VLX LX to GND -0.3 to VIN + 0.3
VFB FB to GND -0.3 to VIN + 0.3
VSDA/SCL SDA/SCL to GND -0.3 to 6.0
VMODE/SYNC, VEN/SET MODE/SYNC and EN/SET to GND -0.3 to 6.0
TJOperating Junction Temperature Range -40 to 150 °C
TLEAD Maximum Soldering Temperature (at leads, 10 sec) 300
Thermal Information2
Symbol Description Value Units
PD Maximum Power Dissipation3 2.0 W
JA Thermal Resistance 50 °C/W
AAT1142
DATA SHEET
800mA Voltage-Scaling Step-Down Converter
4Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201931B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 17, 2012
1. The AAT1142 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and correla-
tion with statistical process controls.
Electrical Characteristics1
L = 2.2μH, CIN = COUT = 10μF, V IN = 3.6V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA =
25°C.
Symbol Description Conditions Min Typ Max Units
Step-Down Converter
VIN Input Voltage 2.7 5.5 V
VUVLO UVLO Threshold
VIN Rising 2.7
Hysteresis 250 mV
VIN Falling 2.0 V
VOUT Output Voltage Tolerance IOUT = 0mA to 800mA, VIN = 2.7V to 5.5V -3.0 3.0 %
VOUT VOUT Programmable Range 0.6 2.0 V
VSLEW Output Voltage Programming Slew Rate COUT = 10μF 10 mV/μs
IQQuiescent Current No Load 35 70 μA
ISHDN Shutdown Current EN/SET = AGND = PGND 1.0
ILIM P-Channel Current Limit 1.0 A
RDS(ON)H High Side Switch On Resistance 0.29
RDS(ON)L Low Side Switch On Resistance 0.24
ILXLEAK LX Leakage Current VIN = 5.5V, VLX = 0V to VIN 1μA
VOUT/
VOUT*VIN
Line Regulation VIN = 2.7V to 5.5V 0.2 %/V
ROUT Output Impedance 250 k
TSStart-Up Time From Enable to Output Regulation 100 μs
FOSC Oscillator Frequency 2.2 MHz
FSYNC SYNC Frequency Range 1.0 3.0
TSD Over-Temperature Shutdown Threshold 140 °C
THYS Over-Temperature Shutdown Hysteresis 15
EN/SET and MODE/SYNC
VEN/SET(L) Enable Threshold Low 0.6 V
VEN/SET(H) Enable Threshold High 1.4
TEN/SET(L) EN/SET Low Time VEN/SET < 0.6V 0.3 75
μs
TEN/SET(H) EN/SET High Time VEN/SET > 1.4V 50 75
TOFF EN/SET Timeout VEN/SET < 0.6V 500
TLATCH EN/SET Latch Timeout VEN/SET > 1.4V 500
IEN/SET Input Low Current VIN = VFB = 5.5V -1.0 1.0 μA
VMODE/SYNC(L) Enable Threshold Low VIN ·
0.4 V
VMODE/SYNC(H) Enable Threshold High VIN ·
0.7
IMODE/SYNC Input Low Current -1.0 1.0 μA
AAT1142
DATA SHEET
800mA Voltage-Scaling Step-Down Converter
5
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201931B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 17, 2012
Characteristics of SDA and SCL Bus Lines
Parameter Symbol
Standard Mode Fast Mode
UnitsMin Max Min Max
SCL Clock Frequency Hold Time for START Condition; After this
Period, the First Clock Pulse is Generated
fSCL 100 400 kHz
tHD;STA 4.0 0.6
μs
LOW Period of the SCL Clock tLOW 4.7 1.3
HIGH Period of the SCL Clock tHIGH 4.0 0.6
Set-up Time for a Repeated START Condition tSU;STA 4.7 0.6
Data in Hold Time tHD;DAT 0 3.45 0 0.9
Data in Set-Up Time tSU;DAT 350 350 μs
Set-Up Time for STOP Condition tSU;STO 4.0 0.6
Bus Free Time Between a STOP and START Condition tBUF 4.7 1.3 μs
Input Low Level VIL VIN· 0.3 VIN · 0.3 V
Input High Level VIH VIN · 0.7 VIN · 0.7
AAT1142
DATA SHEET
800mA Voltage-Scaling Step-Down Converter
6Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201931B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 17, 2012
Typical Characteristics
Efficiency vs. Load
(VOUT = 0.9V)
Output Current (mA)
Efficiency (%)
20
30
40
50
60
70
80
90
100
0 1 10 100 1000
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
VIN = 5.0V
PWM Only
Mode
DC Regulation
(VOUT = 0.9V)
Output Current (mA)
Output Accuracy (%)
-2.0
-1.0
0.0
1.0
2.0
0 1 10 100 1000
VIN = 2.7V VIN = 3.6V
VIN = 4.2V VIN = 5.0V
Efficiency vs. Load
(VOUT = 1.0V)
Output Current (mA)
Efficiency (%)
20
30
40
50
60
70
80
90
100
0 1 10 100 100
0
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
VIN = 5.0V
PWM Only
Mode
DC Regulation
(VOUT = 1.0V)
Output Current (mA)
Output Accuracy (%)
-2.0
-1.0
0.0
1.0
2.0
0 1 10 100 1000
VIN = 2.7V VIN = 3.6V
VIN = 4.2V VIN = 5.0V
Efficiency vs. Load
(VOUT = 1.2V)
Output Current (mA)
Efficiency (%)
20
30
40
50
60
70
80
90
100
0 1 10 100 1000
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
VIN = 5.0V
PWM Only
Mode
DC Regulation
(VOUT = 1.2V)
Output Current (mA)
Output Accuracy (%)
-2.0
-1.0
0.0
1.0
2.0
0 1 10 100 1000
VIN = 2.7V VIN = 3.6V
VIN = 4.2V VIN = 5.0V
AAT1142
DATA SHEET
800mA Voltage-Scaling Step-Down Converter
7
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201931B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 17, 2012
Typical Characteristics
Efficiency vs. Load
(VOUT = 1.8V)
Output Current (mA)
Efficiency (%)
30
40
50
60
70
80
90
100
0 1 10 100 1000
PWM Only
Mode
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
VIN = 5.0V
DC Regulation
(VOUT = 1.8V)
Output Current (mA)
Output Accuracy (%)
-2.0
-1.6
-1.2
-0.8
-0.4
0.0
0.4
0.8
1.2
1.6
2.0
0 1 10 100 100
0
VIN = 4.2V
VIN = 5.0V
VIN = 3.6V
VIN = 2.7V
Soft Start
(VIN = 3.6V; VOUT = 1.8V; IOUT = 800mA)
Output and Enable Voltage
(top) (V)
Inductor Current
(bottom) (A)
-4.0
-3.0
-2.0
-1.0
0.0
1.0
2.0
3.0
4.0
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
Time (50μs/div)
Line Regulation
(VOUT = 1.0V)
Input Voltage (V)
Output Accuracy (%)
-1.00
-0.75
-0.50
-0.25
0.00
0.25
0.50
0.75
1.00
2.5 3.0 3.5 4.0 4.5 5.0 5.5
IOUT = 650mA
IOUT = 0mA
IOUT = 100mA
Output Voltage Accuracy vs. Temperature
(VIN = 3.6V; VOUT = 1.0V; IOUT = 400mA)
Temperature (°
°
C)
Accuracy (%)
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
-40-30-20-100 1020304050607080
Switching Frequency vs. Temperature
(VIN = 3.6V; VOUT = 1.0V; IOUT = 400mA)
Temperature (°
°
C)
Variation (%)
-10.0
-8.0
-6.0
-4.0
-2.0
0.0
2.0
4.0
-40-30-20-10 0 1020304050607080
AAT1142
DATA SHEET
800mA Voltage-Scaling Step-Down Converter
8Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201931B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 17, 2012
Typical Characteristics
P-Channel RDS(ON) vs. Input Voltage
Input Voltage (V)
RDS(ON)H (mΩ
Ω
)
200
250
300
350
400
450
2.5 3 3.5 4 4.5 5 5.5 6 6.5
125°C
100°C
85°C
25°C
N-Channel RDS(ON) vs. Input Voltage
Input Voltage (V)
RDS(ON)L (mΩ
Ω
)
150
200
250
300
350
400
450
2.5 3 3.5 4 4.5 5 5.5 6 6.5
125°C
100°C85°C
25°C
Load Transient Response
(10mA to 400mA; VIN = 3.6V; VOUT = 1.2V)
Output Voltage
(top) (V)
Load and Inductor Current
(bottom) (200mA/div)
Time (50μs/div)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
Load Transient Response
(400mA to 800mA; VIN = 3.6V; VOUT = 1.0V)
Output Voltage
(top) (V)
Load and Inductor Current
(bottom) (200mA/div)
Time (50μs/div)
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
No Load Quiescent Current vs. Input Voltage
(VOUT = 1.8V)
Input Voltage (V)
Supply Current (µA)
20
25
30
35
40
45
50
55
60
2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
85°C
25°C
-40°C
Line Response
(VOUT = 1.2V; IOUT = 650mA)
Output Voltage
(top) (VAC)
Input Voltage
(bottom) (V)
Time (500μs/div)
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
3.0
3.5
4.0
4.5
5.0
5.5
6.0
AAT1142
DATA SHEET
800mA Voltage-Scaling Step-Down Converter
9
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201931B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 17, 2012
Typical Characteristics
Output Ripple
(VIN = 4.2V; VOUT = 0.8V; No Load)
Output Voltage
(top) (V)
Inductor Current
(bottom) (A)
Time (4μs/div)
0.60
0.65
0.70
0.75
0.80
0.85
0.90
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
Output Ripple
(VIN = 4.2V; VOUT = 0.8V; IOUT = 650mA)
Output Voltage
(top) (V)
Inductor Current
(bottom) (A)
Time (200ns/div)
0.72
0.73
0.74
0.75
0.76
0.77
0.78
0.79
0.80
0.81
0.82
0.60
0.62
0.64
0.66
0.68
0.70
0.72
0.74
0.76
0.78
0.80
Output Programming Step
from 0.9V to 1.2V
(VIN = 3.6V; ROUT = 1.85Ω
)
Output Voltage
(top) (V)
Output Current
(bottom) (A)
Time (50μs/div)
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1.10
1.20
1.30
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
Output Programming Step
from 1.2V to 0.9V
(VIN = 3.6V; ROUT = 1.85Ω
)
Output Voltage
(top) (V)
Output Current
(bottom) (A)
Time (50μs/div)
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1.10
1.20
1.30
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
AAT1142
DATA SHEET
800mA Voltage-Scaling Step-Down Converter
10 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201931B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 17, 2012
Functional Description
The AAT1142 is a high performance, 800mA step-down
converter with an input voltage range from 2.7V to 5.5V.
The AAT1142 uses Dynamic Voltage Manage ment, which
allows the system host to quickly set the output voltage
through the integrated I2C or S2Cwire interface. Through
this interface, the host can change the output voltage to
track processor idle and active states, greatly extending
battery life without degrading system performance. I2C
provides an industry-standard, dual-line interface, while
S2Cwire provides a single-line, high-speed serial inter-
face.
The 2.2MHz switching frequency allows the use of small
external components. Only three external components
are needed to program the output from 0.6V to 2.0V.
Typically, one 4.7μF capacitor, one 10μF capacitor, and
one 2.2μH inductor are required.
The integrated low-loss MOSFET switches provide up to
93% efficiency. PFM operation maintains high efficiency
under light load conditions (typically <50mA). Pulling the
MODE/SYNC pin high allows optional PWM Only low noise
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 can be maintained
between 1MHz and 3MHz.
At low input voltages, the converter dynamically adjusts
the operating frequency prior to dropout to maintain the
required duty cycle and provide accurate output regula-
Functional Block Diagram
SCL
LX
Logic
DH
DL
PGND
AGND
PVINVIN
FB
SDA
EN/SET
MODE/SYNC
Control
Logic
Voltage
Reference
Err.
Amp.
AAT1142
DATA SHEET
800mA Voltage-Scaling Step-Down Converter
11
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201931B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 17, 2012
tion. Output regulation is maintained until the dropout
voltage, or minimum input voltage, is reached.
The AAT1142 achieves better than ±0.5% output regula-
tion across the input voltage and output load range.
Maximum continuous load is 800mA. A current limit of
1A (typical) protects the IC and system components
from short-circuit damage. Typical no load quiescent cur-
rent is 35μA.
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 automati-
cally recovers.
Peak current mode control and optimized internal com-
pensation provide high loop bandwidth and excellent
response to input voltage and fast load transient events.
The output voltage is stable across all operating condi-
tions, ensuring fast transitions with no overshoot or ring-
ing. Soft start eliminates output voltage overshoot when
the enable or the input voltage is applied. Under-voltage
lockout prevents spurious start-up events.
Control Loop
The AAT1142 is a peak current mode step-down con-
verter. The current through the P-channel MOSFET (high
side) is sensed for current loop control, as well as short-
circuit and overload protection. A fixed slope compensa-
tion signal is added to the sensed current to maintain
stability for duty cycles greater than 50%. The peak cur-
rent mode loop appears as a voltage-programmed cur-
rent source in parallel with the output capacitor.
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. Loop
stability and fast transient response are maintained
across the entire input and output voltage range with a
small 2.2μH output inductor and 10μF output capacitor.
Soft Start/Enable
Soft start limits the current surge seen at the input and
eliminates output voltage overshoot. When pulled low,
the enable input forces the AAT1142 into a low-power,
non-switching state. The total input current during shut-
down is less than 1μA. The turn-on time from EN to
output regulation is 100μs (typical).
Alternatively, the EN/SET pin serves as the input for
S2Cwire single line control. Details of S2Cwire operation
and timing diagrams are provided in the Applications
Information section of this datasheet.
Current Limit and
Over-Temperature Protection
Switching is terminated after entering current limit for a
series of pulses to minimize power dissipation and
stresses under overload and short-circuit conditions.
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 hys-
teresis. Once an over-temperature or over-current fault
condition is removed, the output voltage automatically
recovers.
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.
AAT1142
DATA SHEET
800mA Voltage-Scaling Step-Down Converter
12 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201931B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 17, 2012
Applications Information
The AAT1142 output voltage may be programmed from
0.6V to 2.0V through I2C or S2Cwire serial interface.
When using I2C or S2Cwire, the output voltage can be
programmed across the entire output voltage range or in
increments as small as ±50mV (see Figure 1).
I2C Serial Interface
The AAT1142 is compatible with the I2C interface, which
is a widely used two-line serial interface. The I2C two-
wire communications bus consists of SDA and SCL lines.
SDA provides data, while SCL provides clock input. SDA
data consists of an address bit sequence followed by a
data bit sequence. SDA data transfer is synchronized to
SCL rising clock edges.
When using the I2C interface, EN/SET is pulled high to
enable the output or low to disable the output. To ensure
a disable event, the EN/SET pulse width must be greater
than the latch time (500μs maximum).
The I2C serial interface requires a master to initiate all
the communications with slave devices. The I2C protocol
is a bidirectional bus allowing both read and write actions
to take place; while the AAT1142 is a slave device and
only supports the write protocol.
The AAT1142 is a receiver-only (or write-only) slave
device and the Read/Write (R/W) bit is set low. The
AAT1142 address is preset to 0x14 (Hex).
I2C START and STOP Conditions
START and STOP conditions are initialized by the I2C bus
master. The master determines the START (beginning)
and STOP (end) of a transfer with the slave device. Prior
to initiating a START or after STOP, both the SDA and
SCL lines are in bus-free mode. Bus-free mode is when
SDA and SCL are both in the high state (see Figure 2).
I2C Address Bit Map
Figure 3 illustrates the address bit map format. The 7-bit
address is sent with the Most Significant Bit (MSB) first
and is valid when SCL is high. This is followed by the R/W
bit in the Least Significant Bit (LSB) location. The R/W
bit determines the direction of the transfer (‘1’ for read,
‘0’ for write). The AAT1142 is a write-only device and
this bit must be set low when communicating with the
AAT1142. The Acknowledge bit (ACK) is set to low by the
AAT1142 slave to acknowledge receipt of the address.
0.0
0.5
1.0
1.5
1.2
2.0
2.5
1 3 5 7 9 111315171921232527293132
I2C/S2Cwire Register
Output Voltage Level (V)
(default)
Figure 1: AAT1142 Graphical Output Voltage
Programming Map.
AAT1142
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SDA
SCL
SD
A
SCL
START STOP
Figure 2: I2C Start and Stop Conditions.
START: A High “1” to Low “0” Transition on the SDA Line While SCL is High “1”
STOP: A Low “0” to High “1” Transition on the SDA Line While SCL is High “1”
SCL 1 2 3456789
SDAA6A5A4A3A2A1A0R/WACK
Slave Address
LSBMSB
Figure 3: I2C Address Bit Map;
7-bit Slave Address (A6-A0), 1-bit Read/Write (R/W), 1-bit Acknowledge (ACK).
AAT1142
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I2C Data Bit Map
Figure 4 illustrates the data bit format. The 8-bit data is
always sent with the most significant bit first and is valid
when SCL is high. The ACK bit is set low by the AAT1142
slave device to acknowledge receipt of the data.
I2C Acknowledge Bit
The ACK bit is the ninth bit in the address and data byte.
The master must first release the SDA line, and then the
slave will pull the SDA line low. The AAT1142 sends a low
bit to acknowledge receipt of each byte. This occurs dur-
ing the ninth clock cycle of Address and Data transfers
(see Figures 4 and 5).
I2C Software Protocol
An I2C master / slave data transfer, detailing the address
and data bits, is shown in Figure 5. The programming
sequence is as follows:
1. Send a start condition
2. Send the I2C slave address with the R/W bit set low
3. Wait for acknowledge within the clock cycle
4. Send the data bits
5. Wait for acknowledge within the clock cycle
6. Send the stop condition
I2C Output Voltage Programming
The AAT1142 output voltage is programmed through the
I2C interface according to Table 1. The data register
encoded on the SCL and SDA lines determines the out-
put voltage set-point after initial start-up. Upon power-
up and prior to I2C programming, the default output
voltage is set to 1.8V.
SCL 1 2 3456789
SDAD7D6D5D4D3D2D1 D0ACK
Data
LSBMSB
Figure 4: I2C Data Bit Map;
8-bit Data (D7-D0), 1-bit Acknowledge (ACK).
Start Slave Address R/W ACK Data ACK Stop
1SCL 23456789 123456789
1100000
7-bit address (0 x14)
0 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1
Figure 5: I2C SCL, SDA Transfer Protocol Example;
7-bit Slave Address (A6-A0 = 0x14), 1-bit Read/Write (R/W = 0), 1-bit Acknowledge (ACK),
8-bit Data (D7-D0), 1-bit Acknowledge (ACK).
AAT1142
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Data Register
Data Bits
Output Voltage (V)D7 D6 D5 D4 D3 D2 D1 D0
1 XX000000 0.60
2 XX000001 0.65
3 XX000010 0.70
4 XX000011 0.75
5 XX000100 0.80
6 X X 0 0 0 1 0 1 0.85
7 X X 0 0 0 1 1 0 0.90
8 XX000111 0.95
9 XX001000 1.00
10 X0001001 1.05
11 XX001010 1.10
12 XX001011 1.15
13 XX001100 1.20 (default)
14 X X 0 0 1 1 0 1 1.25
15 X X 0 0 1 1 1 0 1.30
16 XX001111 1.35
17 XX010000 1.40
18 XX010001 1.45
19 XX010010 1.50
20 XX010011 1.55
21 XX010100 1.60
22 X X 0 1 0 1 0 1 1.65
23 X X 0 1 0 1 1 0 1.70
24 XX010111 1.75
25 XX011000 1.80
26 XX011001 1.85
27 XX011010 1.90
28 XX011011 1.95
29 XX011100 2.00
30 XX011101 2.00
31 X X 0 1 1 1 1 0 2.00
32 XX011111 2.00
Table 1: AAT1142 I2C Output Voltage Programming Map (X = don’t care).
S2Cwire Serial Interface
Skyworks' S2Cwire serial interface is a proprietary high-
speed single-wire interface. The S2Cwire interface records
rising edges of the EN/SET input and decodes them into
one of 32 registers which determines the output voltage,
as shown in Table 2. Each state corresponds to an output
voltage setting.
When using the S2Cwire interface, both I2C inputs should
be tied to the ground return. This disables the I2C func-
tionality.
S2Cwire Serial Interface Timing
The S2Cwire serial interface has flexible timing. Data can
be clocked-in at speeds up to 1MHz. After data has been
submitted, EN/SET is held high to latch the data for a
period TLAT
. The output is subsequently changed to the
predetermined voltage. When EN/SET is set low for a
time greater than TOFF
, the AAT1142 is disabled. When
disabled, the data register is reset to the default value.
AAT1142
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Rising Clock
Edges/Data
Register
Output
Voltage
(V)
Rising Clock
Edges/Data
Register
Output
Voltage
(V)
1 No change 17 1.40
2 0.65 18 1.45
3 0.70 19 1.50
4 0.75 20 1.55
5 0.80 21 1.60
6 0.85 22 1.65
7 0.90 23 1.70
8 0.95 24 1.75
9 1.00 25 1.80
10 1.05 26 1.85
11 1.10 27 1.90
12 1.15 28 1.95
13 1.20 (default) 29 2.00
14 1.25 30 2.00
15 1.30 31 2.00
16 1.35 32 2.00
Table 2: AAT1142 S2Cwire Output Voltage
Programming Map.
Component Selection
Inductor Selection
The step-down converter uses peak current mode con-
trol with slope compensation to maintain stability for
duty cycles greater than 50%. The output inductor value
must be selected so the inductor current down slope
meets the internal slope compensation requirements.
The internal slope compensation for the programmable
AAT1142 is 0.61A/μs. This equates to a slope compensa-
tion that is 75% of the inductor current down slope for a
1.8V output and 2.2μH inductor.
0.75 · V
O
m = = = 0.61
L
0.75 · 1.8V
2.2μH
A
μs
Manufacturer’s specifications list both the inductor DC
current rating, which is a thermal limitation, and the
peak current rating, which is determined by the satura-
tion characteristics. The inductor should not show any
appreciable saturation under normal load conditions.
Some inductors may meet the peak and average current
ratings yet result in excessive losses due to a high DCR.
Always consider the losses associated with the DCR and
its effect on the total converter efficiency when selecting
an inductor.
The 2.2μH CDRH2D14 series Sumida inductor has a
94m DCR and a 1.5A DC current rating. At full 800mA
load, the inductor DC loss is 60mW which gives a 4.8%
loss in efficiency for an 800mA, 1.0V output.
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.
⎛⎞
· 1 -
⎝⎠
VO
VIN
CIN =
VO
VIN
⎛⎞
- ESR · FS
⎝⎠
VPP
IO
⎛⎞
· 1 - = for VIN = 2 · V
O
⎝⎠
VO
VIN
VO
VIN
1
4
CIN(MIN) = 1
⎛⎞
- ESR · 4 · F
S
⎝⎠
VPP
IO
Always examine the ceramic capacitor DC voltage coeffi-
cient characteristics when selecting the proper value. For
example, the capacitance of a 10F, 6.3V, X5R ceramic
S2Cwire Timing Diagram
1
EN/SET
2n-1 n 64
Data Reg 0n
0
THI
TLO TLAT TOFF
AAT1142
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capacitor with 5.0V DC applied is actually about 6μF.
The maximum input capacitor RMS current is:
⎛⎞
IRMS = IO · · 1 -
⎝⎠
VO
VIN
VO
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.
⎛⎞
· 1 - = D · (1 - D) = 0.52 =
⎝⎠
VO
VIN
VO
VIN
1
2
for VIN = 2 · VO
IO
RMS(MAX)
I2
=
The term ⎛⎞
· 1 -
⎝⎠
VO
VIN
VO
VIN appears in both the input voltage
ripple and input capacitor RMS current equations and is
a maximum when VO is twice VIN. This is why the input
voltage ripple and the input capacitor RMS current ripple
are a maximum at 50% duty cycle.
The input capacitor provides a low impedance loop for
the edges of pulsed current drawn by the AAT1142. 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.
A laboratory test set-up typically consists of two long
wires running from the bench power supply to the evalu-
ation board input voltage pins. The inductance of these
wires, along with the low-ESR ceramic input capacitor,
can create a high Q network that may affect converter
performance. This problem often becomes apparent in
the form of excessive ringing in the output voltage dur-
ing load transients. Errors in the loop phase and gain
measurements can also result.
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 induc-
tance cannot be reduced to a level that does not affect
the converter performance, a high ESR tantalum or alu-
minum electrolytic capacitor 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 4.7μF to 10μF X5R
or X7R ceramic capacitor typically provides sufficient bulk
capacitance to stabilize the output during large load tran-
sitions and has the ESR and ESL characteristics necessary
for low output ripple. A smaller capacitor may result in
slightly increased no load output regulation and output
ripple with input voltages above 5V. This should be veri-
fied under actual operating conditions.
The output voltage droop due to a load transient is dom-
inated 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 volt-
age 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-
tion establishes a limit on the minimum value for the
output capacitor with respect to load transients.
The internal voltage loop compensation also limits the
minimum output capacitor value to 4.7F. This is due to
its effect on the loop crossover frequency (bandwidth),
phase margin, and gain margin. Increased output capac-
itance will reduce the crossover frequency with greater
phase margin.
Thermal Calculations
There are three types of losses associated with the
AAT1142 step-down converter: switching losses, conduc-
tion 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 switch-
ing devices. At full load, assuming continuous conduction
mode (CCM), a simplified form of the losses is given by:
PTOTAL
IO
2 · (RDS(ON)H · VO + RDS(ON)L · [VIN - VO])
VIN
=
+ (tsw · FS · IO + IQ) · VIN
AAT1142
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IQ is the step-down converter quiescent current. The
term tsw is used to estimate the full load step-down con-
verter switching losses.
For the condition where the step-down converter is in
dropout at 100% duty cycle, the total device dissipation
reduces to:
PTOTAL = IO
2 · RDS(ON)H + IQ · VIN
Since RDS(ON), quiescent current, and switching losses all
vary with input voltage, the total losses should be inves-
tigated over the complete input voltage range.
Given the total losses, the maximum junction tempera-
ture can be derived from the JA for the TDFN33-12 pack-
age which is 50°C/W.
TJ(MAX) = PTOTAL · ΘJA + TAMB
Layout
The suggested PCB layout for the AAT1142 is used to
help ensure a proper layout.
1. The input capacitor should connect as closely as pos-
sible to VIN and PGND.
2. C1 and L1 should be connected as closely as possi-
ble. The connection of L1 to the LX pin should be as
short as possible.
3. The feedback pin should be separate from any power
trace and connected close to the VOUT terminal.
Sensing along a high-current load trace will degrade
VOUT load regulation.
4. The resistance of the trace from the GND terminal to
PGND should be kept to a minimum. This will help to
minimize any error in DC regulation due to differ-
ences in the potential of the internal signal ground
and the power ground.
5. Connect unused signal pins to ground to avoid
unwanted noise coupling. When using S2Cwire, con-
nect SDA and SCL to ground to disable I2C function-
ality.
6. Connect the exposed paddle (EP) to the GND plane.
Manufacturer Part Number Inductance (μH)
Max DC
Current (A) DCR ()
Size (mm)
LxWxH Type
Sumida CDRH3D16-2R2 2.2 1.20 0.072 3.8x3.8x1.8 Shielded
Sumida CDRH2D14-2R2 2.2 1.50 0.094 3.2x3.2x1.55 Shielded
Taiyo Yuden NR3010T2R2M 2.2 1.10 0.095 3.0x3.0x1.0 Shielded
Taiyo Yuden CBC3225T2R2MR 2.2 1.13 0.080 3.2x2.5x2.5 Non-Shielded
Table 3: Typical Surface Mount Inductors.
Manufacturer Part Number Type Value Voltage Temp. Co. Case
Murata GRM188R60J106ME47D Ceramic 10 6.3 X5R 0603
Murata GRM21BR60J106KE19L Ceramic 10 10 X5R 0805
Murata GRM188R60J475KE19D Ceramic 4.7 6.3 X5R 0603
Murata GRM21BR61A475KA73L Ceramic 4.7 10 X5R 0805
Table 4: Surface Mount Capacitors.
AAT1142
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Ordering Information
Package Marking Part Number (Tape and Reel)
TDFN33-12 AAT1142-1.2
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
TDFN33-121
Top View Bottom View
Detail "A"
Side View
3.00
±
0.05
Index Area Detail "A"
1.70
±
0.05
3.00
±
0.05
0.05
±
0.05
0.23
±
0.05
0.75
±
0.05
2.40
±
0.05
Pin 1 Indicator
(optional)
0.40
±
0.05
0.45
±
0.050.23
±
0.05
0.1 REF
C0.3
All dimensions in millimeters.
1. 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.
AAT1142
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Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved.
Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. These materials, including the information contained herein, are provided by Skyworks as a
service to its customers and may be used for informational purposes only by the customer. Skyworks assumes no responsibility for errors or omissions in these materials or the information contained herein. Sky-
works may change its documentation, products, services, speci cations or product descriptions at any time, without notice. Skyworks makes no commitment to update the materials or information and shall have no
responsibility whatsoever for con icts, incompatibilities, or other dif culties arising from any future changes.
No license, whether express, implied, by estoppel or otherwise, is granted to any intellectual property rights by this document. Skyworks assumes no liability for any materials, products or information provided here-
under, including the sale, distribution, reproduction or use of Skyworks products, information or materials, except as may be provided in Skyworks Terms and Conditions of Sale.
THE MATERIALS, PRODUCTS AND INFORMATION ARE PROVIDED “AS IS” WITHOUT WARRANTY OF ANY KIND, WHETHER EXPRESS, IMPLIED, STATUTORY, OR OTHERWISE, INCLUDING FITNESS FOR A PARTICULAR
PURPOSE OR USE, MERCHANTABILITY, PERFORMANCE, QUALITY OR NON-INFRINGEMENT OF ANY INTELLECTUAL PROPERTY RIGHT; ALL SUCH WARRANTIES ARE HEREBY EXPRESSLY DISCLAIMED. SKYWORKS DOES
NOT WARRANT THE ACCURACY OR COMPLETENESS OF THE INFORMATION, TEXT, GRAPHICS OR OTHER ITEMS CONTAINED WITHIN THESE MATERIALS. SKYWORKS SHALL NOT BE LIABLE FOR ANY DAMAGES, IN-
CLUDING BUT NOT LIMITED TO ANY SPECIAL, INDIRECT, INCIDENTAL, STATUTORY, OR CONSEQUENTIAL DAMAGES, INCLUDING WITHOUT LIMITATION, LOST REVENUES OR LOST PROFITS THAT MAY RESULT FROM
THE USE OF THE MATERIALS OR INFORMATION, WHETHER OR NOT THE RECIPIENT OF MATERIALS HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
Skyworks products are not intended for use in medical, lifesaving or life-sustaining applications, or other equipment in which the failure of the Skyworks products could lead to personal injury, death, physical or en-
vironmental damage. Skyworks customers using or selling Skyworks products for use in such applications do so at their own risk and agree to fully indemnify Skyworks for any damages resulting from such improper
use or sale.
Customers are responsible for their products and applications using Skyworks products, which may deviate from published speci cations as a result of design defects, errors, or operation of products outside of pub-
lished parameters or design speci cations. Customers should include design and operating safeguards to minimize these and other risks. Skyworks assumes no liability for applications assistance, customer product
design, or damage to any equipment resulting from the use of Skyworks products outside of stated published speci cations or parameters.
Skyworks, the Skyworks symbol, and “Breakthrough Simplicity” are trademarks or registered trademarks of Skyworks Solutions, Inc., in the United States and other countries. Third-party brands and names are for
identi cation purposes only, and are the property of their respective owners. Additional information, including relevant terms and conditions, posted at www.skyworksinc.com, are incorporated by reference.