AAT1142
800mA Voltage-Scaling Step-Down Converter
General Description
Features
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 footprint make the AAT1142
the ideal choice for microprocessor core power in
systems such as smartphones.
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VIN Range: 2.7V to 5.5V
VOUT Programmable Range: 0.6V to 2.0V
Dynamic Voltage Management:
— 50mV Output Resolution
— Fast, Stable Response
Serial Control Options:
— I2C Two-Wire Interface
— S2Cwire 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
TSOPJW-12 or TDFN33-12 Package
Temperature Range: -40°C to +85°C
•
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/undershoot or ringing.
•
•
•
•
•
•
•
•
•
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The AAT1142 delivers up to 800mA of output current
while consuming 35µA of typical no load quiescent
current. Dynamic Voltage Management is provided
through I2C or AnalogicTech's 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.
SwitchReg™
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Applications
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The AAT1142 is available in a Pb-free, space-saving 2.85x3.0x1.0mm TSOPJW-12 package or a
Pb-free, low-profile 3x3x0.8mm TDFN33-12 package. The device is rated over the -40°C to +85°C
temperature range.
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
Efficiency vs. Load
(VOUT = 1.8V)
VOUT: 0.6V to 2.0V
800mA Maximum
VIN: 2.7V to 5.5V
100
L1
VIN
LX
AAT1142
FB
C1
10µF
MODE/SYNC
I 2C
S2Cwire*
PGND
SDA
SCL
1142.2006.07.1.0
80
70
VIN = 4.2V
60
VIN = 5.0V
50
PWM Only
Mode
40
EN/SET
AGND
*Optional S2Cwire or I2C Input
Efficiency (%)
C2
4.7µF
VIN = 3.6V VIN = 2.7V
90
2.2µH
30
0
1
10
100
1000
Output Current (mA)
1
AAT1142
800mA Voltage-Scaling Step-Down Converter
Pin Descriptions
Pin #
TSOPJW-12
TDFN33-12
1
12
Symbol
LX
2
11
PGND
3
10
MODE/SYNC
4
5
6
9
8
7
SDA
SCL
EN/SET
7
6
FB
8, 9, 10, 11
121
121
n/a
n/a
4, 5
3
1
2
EP
AGND
VIN
PVIN
N/C
Function
Connect the output inductor to this pin. The switching node is
internally connected to the drain of both high- and low-side
MOSFETs.
Main power ground return pin. Connect to the output and
input capacitor return.
Connect to ground for PFM/PWM mode and optimized efficiency throughout the load range. Connect to high for low
noise PWM Only operation under all operating conditions.
Connect to an external clock for synchronization (PWM Only).
I2C control pin: Data input.
I2C control pin: Clock input.
IC enable pin. Pull high to enable the AAT1142; pull low to
disable the AAT1142. Also serves as S2Cwire input for programmable output voltages.
Feedback input pin. This pin is connected directly to the converter output for programmable output.
Ground connection pin.
Input voltage for the converter.
Input voltage for the power switches.
Not connected.
Exposed paddle (bottom); connect to ground as closely as
possible to the device.
Pin Configuration
TSOPJW-12
(Top View)
LX
PGND
MODE/SYNC
SDA
SCL
EN/SET
1
12
2
11
3
10
4
9
5
8
6
7
TDFN33-12
(Top View)
VIN
AGND
AGND
AGND
AGND
FB
PVIN
N/C
VIN
AGND
AGND
FB
1
12
2
11
3
10
4
9
5
8
6
7
LX
PGND
MODE/SYNC
SDA
SCL
EN/SET
1. VIN and PVIN are tied together in the TSOPJW-12 package.
2
1142.2006.07.1.0
AAT1142
800mA Voltage-Scaling Step-Down Converter
Absolute Maximum Ratings1
Symbol
VIN, PVIN
VLX
VFB
VSDA/SCL
VMODE/SYNC, VEN/SET
TJ
TLEAD
Description
Input Voltage and Input Power to GND
LX to GND
FB to GND
SDA/SCL to GND
MODE/SYNC and EN/SET 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
-0.3 to 6.0
-40 to 150
300
V
V
V
V
V
°C
°C
Value
Units
625
2.0
160
50
mW
W
Thermal Information2
Symbol
Description
TSOPJW-12
TDFN33-124
TSOPJW-12
TDFN33-12
3
PD
Maximum Power Dissipation
θJA
Thermal Resistance
°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.
3. Derate 6.25mW/°C above 25°C.
4. Derate 20mW/°C above 25°C.
1142.2006.07.1.0
3
AAT1142
800mA Voltage-Scaling Step-Down Converter
Electrical Characteristics1
L = 2.2µH, CIN = COUT = 10µF, VIN = 3.6V, TA = -40°C to +85°C, unless otherwise noted. Typical values are
at TA = 25°C.
Symbol
Description
Conditions
Step-Down Converter
VIN
Input Voltage
VUVLO
UVLO Threshold
Output Voltage Tolerance
VOUT
VOUT Programmable Range
Output Voltage Programming
Slew Rate
Quiescent Current
Shutdown Current
P-Channel Current Limit
High Side Switch On Resistance
Low Side Switch On Resistance
LX Leakage Current
VIN = 5.5V, VLX = 0V to VIN
Line Regulation
VIN = 2.7V to 5.5V
IQ
ISHDN
ILIM
RDS(ON)H
RDS(ON)L
ILXLEAK
ΔVOUT/
VOUT*ΔVIN
ROUT
TS
FOSC
FSYNC
TSD
THYS
Output Impedance
Start-Up Time
Oscillator Frequency
SYNC Frequency Range
Over-Temperature Shutdown
Threshold
Over-Temperature Shutdown
Hysteresis
Typ
2.7
VIN Rising
Hysteresis
VIN Falling
IOUT = 0mA to 800mA,
VIN = 2.7V to 5.5V
VOUT
VSLEW
Min
Max Units
5.5
2.7
V
V
mV
V
-3.0
3.0
%
0.6
2.0
V
250
2.0
COUT = 10µF
10
No Load
EN/SET = AGND = PGND
35
mV/µs
70
1.0
1.0
0.29
0.24
1
0.2
%/V
100
2.2
kΩ
µs
MHz
MHz
250
From Enable to Output Regulation
µA
µA
A
Ω
Ω
µA
1.0
3.0
140
°C
15
°C
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 correlation with statistical process controls.
4
1142.2006.07.1.0
AAT1142
800mA Voltage-Scaling Step-Down Converter
Electrical Characteristics1
L = 2.2µH, CIN = COUT = 10µF, VIN = 3.6V, TA = -40°C to +85°C, unless otherwise noted. Typical values are
at TA = 25°C.
Symbol
Description
EN/SET and MODE/SYNC
VEN/SET(L)
Enable Threshold Low
VEN/SET(H)
Enable Threshold High
TEN/SET(L)
EN/SET Low Time
TEN/SET(H)
EN/SET High Time
TOFF
EN/SET Timeout
TLATCH
EN/SET Latch Timeout
IEN/SET
Input Low Current
VMODE/SYNC(L)
Enable Threshold Low
VMODE/SYNC(H)
Enable Threshold High
IMODE/SYNC
Conditions
Min
Typ
Max Units
0.6
1.4
0.3
VEN/SET < 0.6V
VEN/SET > 1.4V
VEN/SET < 0.6V
VEN/SET > 1.4V
VIN = VFB = 5.5V
75
75
500
500
1.0
VIN ×
0.4
50
-1.0
VIN ×
0.7
-1.0
Input Low Current
V
V
µs
µs
µs
µs
µA
V
V
1.0
µA
Characteristics of SDA and SCL Bus Lines
Standard Mode
Parameter
SCL Clock Frequency
Hold Time for START Condition; After
this Period, the First Clock Pulse is
Generated
LOW Period of the SCL Clock
HIGH Period of the SCL Clock
Set-up Time for a Repeated START
Condition
Data in Hold Time
Data in Set-Up Time
Set-Up Time for STOP Condition
Bus Free Time Between a STOP and
START Condition
Input Low Level
Input High Level
Symbol
Min
fSCL
tHD;STA
4.0
tSU;STA
4.7
4.0
4.7
tHD;DAT
tSU;DAT
tSU;STO
tBUF
0
350
4.0
4.7
tLOW
tHIGH
VIL
VIH
Max
Fast Mode
Min
Max
Units
400
0.6
kHz
µs
1.3
0.6
0.6
µs
µs
µs
100
3.45
0
350
0.6
1.3
VIN · 0.3
VIN · 0.7
VIN · 0.7
0.9
µs
ns
µs
µs
VIN · 0.3
V
V
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 correlation with statistical process controls.
1142.2006.07.1.0
5
AAT1142
800mA Voltage-Scaling Step-Down Converter
Typical Characteristics
Efficiency vs. Load
DC Regulation
(VOUT = 0.9V)
(VOUT = 0.9V)
2.0
100
Efficiency (%)
Output Accuracy (%)
VIN = 3.6V VIN = 2.7V
90
VIN = 4.2V
80
70
60
50
40
PWM Only
Mode
VIN = 5.0V
30
20
0
1
10
100
1.0
VIN = 2.7V
VIN = 4.2V
-1.0
0
1
Output Accuracy (%)
Efficiency (%)
(VOUT = 1.0V)
VIN = 4.2V
70
60
PWM Only
Mode
VIN = 5.0V
40
30
1.0
1
10
100
VIN = 2.7V
VIN = 4.2V
1000
0
1
(VOUT = 1.2V)
PWM Only
Mode
60
50
VIN = 5.0V
30
20
0
1
10
Output Current (mA)
6
1000
2.0
Output Accuracy (%)
Efficiency (%)
DC Regulation
(VOUT = 1.2V)
70
40
100
Efficiency vs. Load
VIN = 4.2V
80
10
Output Current (mA)
VIN = 3.6V VIN = 2.7V
90
VIN = 5.0V
-1.0
Output Current (mA)
100
VIN = 3.6V
0.0
-2.0
20
0
1000
2.0
VIN = 3.6V VIN = 2.7V
50
100
DC Regulation
(VOUT = 1.0V)
80
10
Output Current (mA)
Efficiency vs. Load
90
VIN = 5.0V
-2.0
1000
Output Current (mA)
100
VIN = 3.6V
0.0
100
1000
1.0
VIN = 2.7V
VIN = 3.6V
0.0
VIN = 4.2V
VIN = 5.0V
-1.0
-2.0
0
1
10
100
1000
Output Current (mA)
1142.2006.07.1.0
AAT1142
800mA Voltage-Scaling Step-Down Converter
Typical Characteristics
Efficiency vs. Load
DC Regulation
(VOUT = 1.8V)
(VOUT = 1.8V)
2.0
100
Efficiency (%)
Output Accuracy (%)
VIN = 3.6V VIN = 2.7V
90
80
70
VIN = 4.2V
60
VIN = 5.0V
50
PWM Only
Mode
40
30
1.6
1.2
VIN = 5.0V
0.8
VIN = 4.2V
0.4
0.0
VIN = 2.7V
-0.4
-0.8
VIN = 3.6V
-1.2
-1.6
-2.0
0
1
10
100
1000
0
1
Output Current (mA)
10
Soft Start
Line Regulation
(VOUT = 1.0V)
3.5
3.0
3
2.0
2.5
1.0
2
0.0
1.5
-1.0
1
-2.0
0.5
-3.0
0
-4.0
-0.5
Output Accuracy (%)
4.0
1.00
Inductor Current
(bottom) (A)
Output and Enable Voltage
(top) (V)
1000
Output Current (mA)
(VIN = 3.6V; VOUT = 1.8V; IOUT = 800mA)
0.75
0.50
IOUT = 650mA
0.25
0.00
-0.25
-0.50
IOUT = 0mA
IOUT = 100mA
-0.75
-1.00
2.5
3.0
3.5
Time (50µs/div)
4.0
4.5
5.0
5.5
Input Voltage (V)
Output Voltage Accuracy vs. Temperature
Switching Frequency vs. Temperature
(VIN = 3.6V; VOUT = 1.0V; IOUT = 400mA)
(VIN = 3.6V; VOUT = 1.0V; IOUT = 400mA)
2.0
4.0
1.5
2.0
1.0
Variation (%)
Accuracy (%)
100
0.5
0.0
-0.5
-1.0
-2.0
-4.0
-6.0
-8.0
-1.5
-2.0
-40
0.0
-30
-20
-10
0
10
20
30
40
Temperature (°°C)
1142.2006.07.1.0
50
60
70
80
-10.0
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
Temperature (°°C)
7
AAT1142
800mA Voltage-Scaling Step-Down Converter
Typical Characteristics
P-Channel RDS(ON) vs. Input Voltage
N-Channel RDS(ON) vs. Input Voltage
450
450
125°C
400
100°C
RDS(ON)L (mΩ
Ω)
RDS(ON)H (mΩ
Ω)
400
85°C
350
300
25°C
250
125°C
350
100°C
250
25°C
200
150
2.5
200
2.5
3
3.5
4
4.5
5
5.5
6
6.5
Input Voltage (V)
3
3.5
4
4.5
5
Load Transient Response
(400mA to 800mA; VIN = 3.6V; VOUT = 1.0V)
6.5
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
-0.1
-0.2
Load and Inductor Current
(bottom) (200mA/div)
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Output Voltage
(top) (V)
Load Transient Response
Time (50µs/div)
No Load Quiescent Current vs. Input Voltage
Line Response
(VOUT = 1.8V)
(VOUT = 1.2V; IOUT = 650mA)
60
0.2
6.0
0.1
5.5
0.0
5.0
-0.1
4.5
-0.2
4.0
-0.3
3.5
-0.4
3.0
50
85°C
45
25°C
40
-40°C
35
30
25
20
2.5
3.0
3.5
4.0
4.5
Input Voltage (V)
5.0
5.5
6.0
Output Voltage
(top) (VAC)
55
Input Voltage
(bottom) (V)
Supply Current (µA)
6
(10mA to 400mA; VIN = 3.6V; VOUT = 1.2V)
Time (50µs/div)
8
5.5
Input Voltage (V)
Load and Inductor Current
(bottom) (200mA/div)
Output Voltage
(top) (V)
85°C
300
Time (500µs/div)
1142.2006.07.1.0
AAT1142
800mA Voltage-Scaling Step-Down Converter
Typical Characteristics
Output Ripple
Output Ripple
(VIN = 4.2V; VOUT = 0.8V; No Load)
(VIN = 4.2V; VOUT = 0.8V; IOUT = 650mA)
Output Voltage
(top) (V)
0.80
0.06
0.04
0.75
0.70
0.02
0.65
0.00
-0.02
0.60
0.82
0.80
0.81
0.78
0.80
0.76
0.79
0.74
0.78
0.72
0.77
0.70
0.76
0.68
0.75
0.66
0.74
0.64
0.73
0.62
Time (200ns/div)
Output Programming Step
from 0.9V to 1.2V
Output Programming Step
from 1.2V to 0.9V
(VIN = 3.6V; ROUT = 1.85Ω
Ω)
(VIN = 3.6V; ROUT = 1.85Ω
Ω)
1.30
0.90
1.20
0.85
1.20
0.85
1.10
0.80
1.10
0.80
1.00
0.75
1.00
0.75
0.90
0.70
0.90
0.70
0.80
0.65
0.80
0.65
0.70
0.60
0.70
0.60
0.60
0.55
0.60
0.55
0.50
0.50
0.50
0.50
0.40
0.45
0.40
0.45
0.30
0.40
0.30
Time (50µs/div)
1142.2006.07.1.0
Output Voltage
(top) (V)
0.90
Output Current
(bottom) (A)
1.30
Output Current
(bottom) (A)
Output Voltage
(top) (V)
0.60
0.72
Time (4µs/div)
Inductor Current
(bottom) (A)
0.08
Inductor Current
(bottom) (A)
0.85
Output Voltage
(top) (V)
0.10
0.90
0.40
Time (50µs/div)
9
AAT1142
800mA Voltage-Scaling Step-Down Converter
Functional Block Diagram
VIN
FB
PVIN
MODE/SYNC
Voltage
Reference
Err.
Amp.
DH
Logic
EN/SET
LX
DL
SDA
SCL
Control
Logic
PGND
AGND
Functional Description
The AAT1142 is a high performance, 800mA stepdown converter with an input voltage range from
2.7V to 5.5V. The AAT1142 uses Dynamic Voltage
Management, 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, highspeed serial interface.
The 2.2MHz switching frequency allows the use of
small external components. Only three external
components are needed to program the output
10
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 accu-
1142.2006.07.1.0
AAT1142
800mA Voltage-Scaling Step-Down Converter
rate output regulation. Output regulation is maintained until the dropout voltage, or minimum input
voltage, is reached.
The AAT1142 achieves better than ±0.5% output
regulation 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 current 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 automatically recovers.
Peak current mode control and optimized internal
compensation provide high loop bandwidth and
excellent response to input voltage and fast load
transient events. The output voltage is stable across
all operating conditions, ensuring fast transitions
with no overshoot or ringing. 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
converter. The current through the P-channel
MOSFET (high side) is sensed for current loop
control, as well as short-circuit and overload protection. A fixed slope compensation signal is added
to the sensed current to maintain stability for duty
cycles greater than 50%. The peak current mode
loop appears as a voltage-programmed current
source in parallel with the output capacitor.
The output of the voltage error amplifier programs
the current mode loop for the necessary peak
switch current to force a constant output voltage for
all load and line conditions. Internal loop compen-
1142.2006.07.1.0
sation 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 shutdown 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 hysteresis. 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.
11
AAT1142
800mA Voltage-Scaling Step-Down Converter
LX
L1
2.2µH
VOUT
C4
(optional)
0.1µF
C2
10µF
U1
1
2
3
4
1
2
VIN
JP1
VIN
5
6
R5
(optional)
1.8K
SDA
SCL
R4
1.8K
LX
VIN
PGND
AGND
MODE/SYNC AGND
SDA
AGND
SCL
AGND
EN/SET
FB
AAT1142
TSOPJW-12
1
2
12
VIN
VIN
11
C1
4.7µF
10
C3
(optional)
10µF
9
R1
0
8
7
VIN
R2
(optional)
R3
10K
1
2
3
JP2
JP3
U1 AAT1142 TSOPJW-12
L1 CDRH2D14/2R2
C1 4.7µF 10V 0805 X5R
C2 10µF 10V 0805 X5R
C3 10µF optional
C4 0.1µF optional
R1 0Ω 0603
R2 optional 0603
R3 10K 0603
R4, R5 1.8K 0603
Figure 1: AAT1142 Evaluation Board Schematic.
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 2).
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 out-
12
put. 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 3).
1142.2006.07.1.0
AAT1142
800mA Voltage-Scaling Step-Down Converter
Output Voltage Level (V)
2.5
2.0
1.8
(default)
1.5
1.0
0.5
0.0
1
3
5
7
9
11
13
15
17
19
21
23
25
27
29
31 32
I2C/S2Cwire Register
Figure 2: AAT1142 Graphical Output Voltage Programming Map.
START
STOP
SDA
SDA
SCL
SCL
Figure 3: 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"
I2C Address Bit Map
Figure 4 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
1142.2006.07.1.0
(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.
13
AAT1142
800mA Voltage-Scaling Step-Down Converter
SCL
1
4
3
2
5
6
8
7
MSB
SDA
9
LSB
A6
A5
A4
A3
A2
A1
A0
R/W
ACK
Slave Address
Figure 4: I2C Address Bit Map;
7-bit Slave Address (A6-A0), 1-bit Read/Write (R/W), 1-bit Acknowledge (ACK).
I2C Data Bit Map
I2C Software Protocol
Figure 5 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.
An I2C master / slave data transfer, detailing the
address and data bits, is shown in Figure 6. 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 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 during the ninth clock cycle
of Address and Data transfers (see Figures 5 and 6).
SCL
1
4
3
2
5
6
8
7
MSB
SDA
9
LSB
D7
D6
D5
D4
D3
D2
D1
D0
ACK
Data
Figure 5: I2C Data Bit Map;
8-bit Data (D7-D0), 1-bit Acknowledge (ACK).
SCL
1
2
3
0
0
1
4
5
6
7
0
0
Slave Address
Start
0
1
8
9
R/W
ACK
0
0/1
1
2
3
4
0/1
0/1
0/1
5
6
7
8
0/1
0/1
0/1
0/1
Data
0/1
9
ACK Stop
0/1
7-bit address (0x14)
Figure 6: 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).
14
1142.2006.07.1.0
AAT1142
800mA Voltage-Scaling Step-Down Converter
I2C Output Voltage Programming
determines the output voltage set-point after initial
start-up. Upon power-up and prior to I2C programming, the default output voltage is set to 1.8V.
The AAT1142 output voltage is programmed
through the I2C interface according to Table 1. The
data register encoded on the SCL and SDA lines
Data
Register
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
Data Bits
D7 D6 D5 D4 D3 D2 D1 D0
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
0
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
Output
Voltage
(V)
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
1.05
1.10
1.15
1.20
1.25
1.30
1.35
1.40
1.45
1.50
1.55
1.60
1.65
1.70
1.75
1.80 (default)
1.85
1.90
1.95
2.00
2.00
2.00
2.00
Table 1: AAT1142 I2C Output Voltage Programming Map (X = don’t care).
1142.2006.07.1.0
15
AAT1142
800mA Voltage-Scaling Step-Down Converter
S2Cwire Serial Interface
S2Cwire Serial Interface Timing
AnalogicTech's 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.
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.
When using the S2Cwire interface, both I2C inputs
should be tied to the ground return. This disables
the I2C functionality.
S2Cwire Timing Diagram
THI
TLO
TOFF
T LAT
EN/SET
1
Data Reg
2
n-1
n ≤ 64
0
S2Cwire Output Voltage Programming
The AAT1142 is programmed through the S2Cwire
interface according to Table 2. The rising clock
edges received through the EN/SET pin corresponding to a given data register determine the
output voltage set-point. Upon power-up and prior
to S2Cwire programming, the default output voltage
is set to 1.8V.
n-1
Rising
Clock
Edges/
Data
Register
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
0
Output
Voltage
(V)
Rising
Clock
Edges/
Data
Register
Output
Voltage
(V)
No change
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
1.05
1.10
1.15
1.20
1.25
1.30
1.35
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
1.40
1.45
1.50
1.55
1.60
1.65
1.70
1.75
1.80 (default)
1.85
1.90
1.95
2.00
2.00
2.00
2.00
Table 2: AAT1142 S2Cwire Output Voltage
Programming Map.
16
1142.2006.07.1.0
AAT1142
800mA Voltage-Scaling 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 internal slope compensation for
the programmable AAT1142 is 0.61A/µsec. This
equates to a slope compensation that is 75% of the
inductor current down slope for a 1.8V output and
2.2µH inductor.
m=
0.75 ⋅ VO 0.75 ⋅ 1.8V
A
=
= 0.61
L
2.2µH
µsec
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 2.2µH CDRH2D14 series Sumida inductor has
a 94mΩ 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.
CIN =
⎛ VPP
⎞
- ESR · FS
⎝ IO
⎠
VO ⎛
V ⎞
1
· 1 - O = for VIN = 2 · VO
VIN ⎝
VIN ⎠
4
CIN(MIN) =
1
⎛ VPP
⎞
- ESR · 4 · FS
⎝ IO
⎠
Always examine the ceramic capacitor DC voltage
coefficient characteristics when selecting the proper value. For example, the capacitance of a 10μF,
6.3V, X5R ceramic capacitor with 5.0V DC applied
is actually about 6µF.
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
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.
VO ⎛
V ⎞
· 1- O
VIN ⎝
VIN ⎠
IRMS(MAX) =
VO
IO
2
⎛
V ⎞
· 1- O
The term VIN ⎝ VIN ⎠ appears in both the input
voltage ripple and input capacitor RMS current
equations and is a maximum when VO is twice VIN.
This is why the input voltage ripple and the input
capacitor RMS current ripple are a maximum at
50% duty cycle.
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
1142.2006.07.1.0
17
AAT1142
800mA Voltage-Scaling Step-Down Converter
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.
current demand. The relationship of the output voltage droop during the three switching cycles to the
output capacitance can be estimated by:
COUT =
Proper placement of the input capacitor (C1) is
shown in the evaluation board layout in Figure 7.
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 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 transitions 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
verified under actual operating conditions.
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
18
3 · ΔILOAD
VDROOP · FS
Once the average inductor current increases to the
DC load level, the output voltage recovers. The
above equation establishes a limit on the minimum
value for the output capacitor with respect to load
transients.
The internal voltage loop compensation also limits
the minimum output capacitor value to 4.7μF. This
is due to its effect on the loop crossover frequency
(bandwidth), phase margin, and gain margin.
Increased output capacitance will reduce the
crossover frequency with greater phase margin.
Thermal Calculations
There are three types of losses associated with the
AAT1142 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 stepdown converter switching losses.
For the condition where the step-down converter is
in dropout at 100% duty cycle, the total device dissipation reduces to:
PTOTAL = IO2 · RDS(ON)H + IQ · VIN
1142.2006.07.1.0
AAT1142
800mA Voltage-Scaling Step-Down Converter
Since RDS(ON), quiescent current, and switching
losses all vary with input voltage, the total losses
should be investigated over the complete input
voltage range.
Given the total losses, the maximum junction temperature can be derived from the θJA for the
TSOPJW-12 package which is 160°C/W.
TJ(MAX) = PTOTAL · ΘJA + TAMB
Layout
The suggested PCB layout for the AAT1142 in a
TSOPJW-12 package is shown in Figures 7 and 8.
The following guidelines should be used to help
ensure a proper layout.
1. The input capacitor (C2) should connect as
closely as possible to VIN (Pin 12) and PGND
(Pin 2).
Figure 7: AAT1142 Evaluation Board
Top Side Layout (TSOPJW-12 Package).
1142.2006.07.1.0
2. C1 and L1 should be connected as closely as
possible. The connection of L1 to the LX pin
(Pin 1) should be as short as possible.
3. The feedback pin (Pin 7) 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 (Pin 2) 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.
5. Connect unused signal pins to ground to avoid
unwanted noise coupling. When using S2Cwire,
connect SDA and SCL to ground to disable I2C
functionality.
6. When using the TDFN33-12 package, connect
the exposed paddle (EP) to the GND plane.
Figure 8: AAT1142 Evaluation Board
Bottom Side Layout (TSOPJW-12 Package).
19
AAT1142
800mA Voltage-Scaling Step-Down Converter
Manufacturer
Sumida
Sumida
Taiyo Yuden
Taiyo Yuden
Part Number
Inductance
(µH)
Max DC
Current (A)
DCR
Ω)
(Ω
Size (mm)
LxWxH
Type
CDRH3D16-2R2
CDRH2D14-2R2
NR3010T2R2M
CBC3225T2R2MR
2.2
2.2
2.2
2.2
1.20
1.50
1.10
1.13
0.072
0.094
0.095
0.080
3.8x3.8x1.8
3.2x3.2x1.55
3.0x3.0x1.0
3.2x2.5x2.5
Shielded
Shielded
Shielded
Non-Shielded
Table 3: Typical Surface Mount Inductors.
Manufacturer
MuRata
MuRata
MuRata
MuRata
Part Number
Type
Value
Voltage
Temp. Co.
Case
GRM188R60J106ME47D
GRM21BR60J106KE19L
GRM188R60J475KE19D
GRM21BR61A475KA73L
Ceramic
Ceramic
Ceramic
Ceramic
10
10
4.7
4.7
6.3
10
6.3
10
X5R
X5R
X5R
X5R
0603
0805
0603
0805
Table 4: Surface Mount Capacitors.
20
1142.2006.07.1.0
AAT1142
800mA Voltage-Scaling Step-Down Converter
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
TSOPJW-12
TDFN33-12
RIXYY
AAT1142ITP-1.8-T1
AAT1142IWP-1.8-T1
All AnalogicTech products are offered in Pb-free packaging. The term “Pb-free” means
semiconductor products that are in compliance with current RoHS standards, including
the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more
information, please visit our website at http://www.analogictech.com/pbfree.
Package Information
TSOPJW-12
2.85 ± 0.20
+ 0.10
- 0.05
2.40 ± 0.10
0.20
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.
1142.2006.07.1.0
21
AAT1142
800mA Voltage-Scaling Step-Down Converter
TDFN33-12
2.40 ± 0.05
Detail "B"
3.00 ± 0.05
Index Area
(D/2 x E/2)
0.3 ± 0.10 0.16 0.375 ± 0.125
0.075 ± 0.075
3.00 ± 0.05
1.70 ± 0.05
Top View
Bottom View
Pin 1 Indicator
(optional)
0.23 ± 0.05
Detail "A"
0.45 ± 0.05
0.1 REF
0.05 ± 0.05
0.229 ± 0.051
+ 0.05
0.8 -0.20
7.5° ± 7.5°
Option A:
C0.30 (4x) max
Chamfered corner
Side View
Option B:
R0.30 (4x) max
Round corner
Detail "B"
Detail "A"
All dimensions in millimeters.
© Advanced Analogic Technologies, Inc.
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or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice.
Customers are advised to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. AnalogicTech
warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with AnalogicTech’s standard warranty. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed.
AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085
Phone (408) 737-4600
Fax (408) 737-4611
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