DATA SHEET
AAT1272
1.5A Step-Up Current Regulator for Flash LEDs
General Description
Features
The AAT1272 is a high-efficiency, high-current boost
converter capable of 1.5A typical output current. It is an
ideal power solution for LED photo flash applications in
all single cell Li-ion powered products.
• VIN Range: 2.7V to 5.5V
• Dual Channel Output
• Up to 1.5A Regulated Output Current (750mA per
channel)
• Up to 85% Efficiency with Small Inductor (1μH)
• 2 MHz Switching Frequency
• Separate Flash Enable
• User-Programmable Safety Timer
• Single Resistor Sets Flash and Movie Mode Current
• Two Wire, I2C Compliant Serial Interface
▪ Fast, 400kHz Serial Transfer Rate
▪ 16 Level Movie-mode Current
▪ Flash/Movie-mode
▪ Current Output Channel Control
▪ Safety Timer
• True Load Disconnect
• Input Current Limit
• Over-Voltage (Open LED, Open Circuit), Short Circuit,
and Over-Temperature Protection
• Shutdown Current < 1.0μA
• 14-pin TDFN 3x3 mm Package
• -40°C to +85°C Temperature Range
The AAT1272 maintains output current regulation by
switching the internal high-side and low-side switch
transistors. The transistor switches are pulse-width
modulated at a fixed frequency of 2MHz. The high
switching frequency allows the use of a small inductor
and output capacitor, making the AAT1272 ideally suited
for small battery-powered applications.
An industry-standard I2C serial digital input is used to
enable, disable and set the movie-mode current for each
flash LED with up to 16 movie-mode settings. The
AAT1272 also includes a separate Flash Enable input to
initiate both the flash operation and the default timer,
which can be used either to terminate a flash event at the
end of a user-programmed delay or as a safety feature.
The maximum flash and movie-mode current is set by one
external resistor; the ratio of Flash to Movie-mode current
is set at approximately 7.3:1. One or two LEDs can be
connected to the AAT1272; in the case of two LEDs the
output current is matched between each diode.
The AAT1272 contains a thermal management system to
protect the device in the event of an output short-circuit
condition. Built-in circuitry prevents excessive inrush
current during start-up. The shutdown feature reduces
quiescent current to less than 1.0μA.
Applications
•
•
•
•
•
Digital Still Cameras (DSCs)
LED Photo Flash/Torch
Mobile Handsets
MP3 Players
PDAs and Notebook PCs
The AAT1272 is available in a Pb-free, thermally-enhanced
14-pin 3x3mm TDFN package.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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1
DATA SHEET
AAT1272
1.5A Step-Up Current Regulator for Flash LEDs
Typical Application
L1
1μH
SW
IN
High Current Flash LEDs
OUT
CIN
2.2μF
VBAT
COUT
2.2μF
I2C
Interface
AAT1272
Flash
Enable
FLEN
Enable
EN
FLOUTA
SDA
SDA
SCL
SCL
FLOUTB
CT
CT
RSET AGND PGND FLGND
RSET
107kΩ
Pin Descriptions
Pin #
Symbol
1
CT
2
EN
3
FLEN
4
AGND
5
IN
6
SW
7
PGND
8
OUT
9
10
SCL
SDA
11
FLOUTB
12
FLGND
13
FLOUTA
14
RSET
EP
2
Function
Flash timer control input. Connect a capacitor between CT and AGND to set maximum duration of the flash
pulse. To disable the flash timer, connect CT to AGND.
Enable input. EN is an active HIGH asserted input. EN must be strobed low-to-high to enable the AAT1272 to
accept I2C programming instructions.
Flash enable pin. A low-to-high transition on the FLEN pin initiates a flash pulse and starts the flash timer.
Analog ground pin. Connect AGND to PGND, GND, and FLGND at a single point as close to the AAT1272 as
possible.
Power input. Connect IN to the input power supply voltage. Connect a 2.2μF or larger ceramic capacitor from
IN to PGND as close as possible to the AAT1272
Boost converter switching node. Connect a 1μH inductor between SW and IN.
Power ground pin. Connect PGND to AGND, GND, and FLGND at a single point as close to the AAT1272 as possible.
Power output of the boost converter. Connect a 2.2μF or larger ceramic capacitor from OUT to PGND as close
as possible to the AAT1272. Connect OUT to the anode(s) of the Flash LED(s).
I2C interface serial control line.
I2C interface serial data/address.
Flash Output B. Connect cathode of Flash LEDB to FLOUTB. For a single flash LED, connect FLOUTB and
FLOUTA together. For two flash LEDs, each output will conduct 50% of the total flash output current.
Flash ground pin. Connect FLGND to PGND, GND, and AGND at a single point as close to the AAT1272 as
possible.
Flash Output A. Connect cathode of Flash LEDA to FLOUTA. For a single flash LED, connect FLOUTA and
FLOUTB together. For two flash LEDs, each output will conduct 50% of the total flash output current.
Flash current setting input. A 107kΩ resistor from RSET to AGND sets the maximum flash current available
at FLOUTA and FLOUTB to 1.5A. Each FLOUTA and FLOUTB channel will conduct 50% of the maximum programmed current. The AAT1272’s flash-to-movie-mode ratio is fixed at 7.3:1.
Exposed paddle (bottom); Connect EP to PGND as close as possible to the AAT1272.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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DATA SHEET
AAT1272
1.5A Step-Up Current Regulator for Flash LEDs
Pin Configuration
TDFN33-14
(Top View)
CT
EN
FLEN
AGND
IN
SW
PGND
1
14
2
13
3
4
12
EP
11
5
10
6
9
7
8
RSET
FLOUTA
FLGND
FLOUTB
SDA
SCL
OUT
Absolute Maximum Ratings1
(TA = 25°C unless otherwise noted.)
Symbol
IN, SW, OUT
RSET, EN/SET, FLEN, FLINH, CT,
FLOUTA, FLOUTB
TJ
Ts
TLEAD
Description
Value
Units
Maximum Rating
-0.3 to 6.0
V
Maximum Rating
VIN + 0.3
V
-40 to 150
-65 to 150
300
C
C
C
Value
Units
50
2
C/W
W
Operating Temperature Range
Storage Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
Recommended Operating Conditions
Symbol
θJA
PD
Description
Thermal Resistance
Maximum Power Dissipation
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. The AAT1272 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.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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3
DATA SHEET
AAT1272
1.5A Step-Up Current Regulator for Flash LEDs
Electrical Characteristics1
VIN = 3.6V; CIN = 2.2μF; COUT = 2.2μF; L = 1μH; RSET = 107kΩ; TA = -40°C to 85°C, unless otherwise noted. Typical
values are TA = 25°C.
Symbol
Description
Conditions
Power Supply
Input Voltage Range
VIN
VOUT(MAX)
Maximum Output Voltage
IIN(Q)
Supply Current
ISHDN(MAX)
IFL(TOTAL)
IFL(MATCH)
VIN Shutdown Current
Total Output Current, Flash Mode
FLOUTA and FLOUTB Current Matching
IMM(LOAD)
Total Output Current, Movie Mode
fOSC
tDEFAULT
TSD
TSD(HYS)
I2C Control –
Switching Frequency
Default ON Time
Thermal Shutdown Threshold
Thermal Shutdown Hysteresis
SDA, SCL
VIL
Input Threshold Low
VIH
Input Threshold High
II
VOL
fSCL
tLOW
tHIGH
Input Current
Output Logic Low (SDA)
SCL Clock Frequency
SCL Clock Low Period
SCL Clock High Period
tHD_STA
Hold Time START Condition
tSU_STA
Setup Time for Repeat START
tSU_DAT
SDA Data Setup Time
tHD_DAT
SDA Data Hold Time
tSU_STO
Setup time for STOP Condition
Bus Free Time between STOP and
tBUF
START Condition
EN, FLEN Logic Control
VEN(L),
EN, FLEN Input Low Threshold
VFLEN(L)
VEN(H),
EN, FLEN Input High Threshold
VFLEN(H)
tFLEN_OND
FLEN ON Delay Time
tFLEN_OFFD
FLEN OFF Delay Time
Min
Typ
2.7
EN = FLEN = IN, Set FL Load = 1.5A
EN = IN, FLEN = AGND
EN = FLEN = GND
RSET = 107k; FLOUTA + FLOUTB
RSET = 107k , Movie Mode Current Set =
100%; FLOUTA + FLOUTB
TA = 25˚C
CT = 74nF
0.67
0.23
Max
Units
5.5
5.5
1
V
V
1
1.2
1.5
1.5
10
μA
A
%
206
mA
2.0
600
140
15
2.5
MHz
ms
°C
°C
0.4
V
1.4
V
-1.0
1.0
0.4
400
0.6
μA
V
kHz
μs
μs
μs
μs
ns
μs
μs
1.3
μs
IPULLUP = 3mA
0
1.3
0.6
0.6
0.6
100
0.9
0.4
1.4
EN = AGND
EN = AGND
mA
V
V
40
10
μs
μs
1. The AAT1272 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 • sales@skyworksinc.com • www.skyworksinc.com
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DATA SHEET
AAT1272
1.5A Step-Up Current Regulator for Flash LEDs
I2C Interface Timing Details
SDA
TSU_DAT
TLOW
THD_STA
TBUF
SCL
THD_STA
THD_DAT
THIGH
TSU_STA
TSU_STO
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DATA SHEET
AAT1272
1.5A Step-Up Current Regulator for Flash LEDs
Typical Characteristics
Flash Mode Efficiency vs. Input Voltage
90
100
320mA, VF = 2.91V
540mA, VF = 3.00V
700mA, VF = 3.04V
900mA, VF = 3.04V
1500mA, VF = 3.15V
1200mA, VF = 3.27V
80
102mA/ch
52mA/ch
26mA/ch
85
Efficiency (%)
90
Efficiency (%)
Movie Mode Efficiency vs. Input Voltage
70
60
50
80
75
70
65
60
55
40
2.7
3.1
3.5
3.9
4.3
4.7
5.1
50
2.7
5.5
3.1
3.5
5.1
5.5
Boost Switching Frequency vs. Input Voltage
Shutdown Current vs. Input Voltage
(VEN/SET = VFLEN = 0V)
3
0.03
Shutdown Current (µA)
Switching Frequency (MHz)
4.7
Input Voltage (V)
2.5
2
1.5
1
85°C
25°C
-40°C
0.5
0.025
0.02
0.015
0.01
0.005
25°C
-40°C
0
0
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
2.7
3.1
Input Voltage (V)
900
115
Output Current (mA)
120
800
700
600
500
400
300
85°C
25°C
-40°C
200
100
3.9
4.3
Input Voltage (V)
4.7
5.1
5.5
4.7
5.1
110
105
100
95
90
FLOUTA
FLOUTB
85
80
0
3.5
4.3
(IFLOUTX = 103mA/Ch; VIN = 3.6V; L = 1µH)
1000
3.1
3.9
Movie Mode Current vs. Temperature
(VEN = VFLEN = 3.6V)
2.7
3.5
Input Voltage (V)
Supply Current vs. Input Voltage
Supply Current (µA)
4.3
Input Voltage (V)
(Movie Mode; L = 1µH)
6
3.9
5.5
-40
-15
10
35
Temperature (°C)
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85
DATA SHEET
AAT1272
1.5A Step-Up Current Regulator for Flash LEDs
Typical Characteristics
Movie Mode Output Ripple
(IFLOUTX = 103mA/Channel; L = 1µH)
(IFLOUTX = 103mA/ch; VIN = 3.6V; L = 1µH)
LED Current Accuracy (%)
Movie Mode LED Current Accuracy vs. Input Voltage
10
8
VOUT
(AC Coupled)
(50mV/div)
6
4
2
0
VINDUCTOR
(2V/div)
-2
0V
-4
-6
IINDUCTOR
(100mA/div)
FLOUTA
FLOUTB
-8
-10
2.7
3.1
3.5
3.9
4.3
4.7
5.1
100mA
5.5
Input Voltage (V)
Time (500ns/div)
Flash Mode Output Ripple
Flash LED Current Matching vs. Temperature
(IFLOUTX = 750mA/ch; VIN = 4V; L = 1µH)
(IFLOUTX = 750mA/Ch; VIN = 4.2V; L = 1µH)
800
790
VINDUCTOR
(2V/div)
Output Current (mA)
VOUT
(AC Coupled)
(50mV/div)
0V
IINDUCTOR
(50mA/div)
780
770
760
750
740
730
720
FLOUTA
FLOUTB
710
700
-40
1.65A
-15
10
60
85
Temperature (°C)
Time (200ns/div)
Flash On Time Delay vs. Input Voltage
Flash Timeout Delay vs. CT Capacitor
(IFLOUTX = 750mA/ch; COUT = 2.2µF; L = 1µH)
(IFLOUTX = 750mA/ch; VIN = 3.6V)
80
1200
Flash Timeout (ms)
70
TFLEN_OND (µs)
35
60
50
40
30
20
-40°C
25°C
85°C
10
0
2.7
3.1
3.5
3.9
4.3
Input Voltage (V)
4.7
5.1
5.5
1000
800
600
400
200
0
0
20
40
60
80
100
120
140
CT Capacitor (nF)
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DATA SHEET
AAT1272
1.5A Step-Up Current Regulator for Flash LEDs
Typical Characteristics
Movie Mode Line Transient
Flash Turn On Characteristic
(IFLOUTX = 103mA/ch; VIN = 4.2V to 3.6V)
(IFLOUTX = 750mA/ch; VIN = 3.6V; L = 1µH)
4.2V
VIN
(500mV/div)
3.6V
IFLOUTx
(AC Coupled)
(50mA/div)
VFLEN
(5V/div)
VOUT
(2V/div)
0V
0V
VSINK
(2V/div)
0V
IFLOUTX
(1A/div)
0V
Time (50µs/div)
Time (50µs/div)
Movie Mode to Flash Turn On Characteristic
Movie Mode Turn On Characteristic
(IFLOUTX = 103mA to 750mA/ch; VIN = 3.6V; L = 1µH)
(IFLOUTX = 103mA/ch; VIN = 3.6V; L = 1µH)
VFLEN
(2V/div)
VOUT
(2V/div)
SDA
(5V/div)
VOUT
(2V/div)
0V
2V
0V
0V
VSINK
(500mV/div)
VSINK
(2V/div)
0V
IFLOUTX
(1A/div)
IFLOUTX
(100mA/div)
0A
0V
0A
Time (50µs/div)
Movie Mode Transition Characteristic
Flash Timeout vs. Temperature
(IFLOUTX = 102mA to 188mA/ch; COUT = 0.22µF;
VIN = 3.6V; L = 1µH)
(IFLOUTX = 750mA/ch; VIN = 3.6V; CT = 47nF)
0V
0V
VSINK
(2V/div)
IFLOUTX
(100mA/div)
500
Flash Timeout (ms)
SDA
(5V/div)
VOUT
(2V/div)
0V
450
400
350
300
250
200
0A
-40
Time (100µs/div)
8
Time (100µs/div)
-15
10
35
Temperature (°C)
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85
DATA SHEET
AAT1272
1.5A Step-Up Current Regulator for Flash LEDs
Typical Characteristics
EN, FLEN Low Threshold Voltage
vs. Input Voltage
1.4
1.4
1.3
1.3
VEN/SET(L), VFLEN(L) (V)
VEN/SET(H), VFLEN(H) (V)
EN, FLEN High Threshold Voltage
vs. Input Voltage
1.2
1.1
1.0
0.9
0.8
0.7
85°C
25°C
-40°C
0.6
0.5
85°C
25°C
-40°C
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.4
2.7
3.1
3.5
3.9
4.3
Input Voltage (V)
4.7
5.1
5.5
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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DATA SHEET
AAT1272
1.5A Step-Up Current Regulator for Flash LEDs
Functional Block Diagram
IN
SW
OUT
FLOUTA
FLOUTB
EN
FLEN
SCL
Control
SDA
RSET
CT
AGND PGND FLGND
Functional Description
The AAT1272 is a boost converter with a current-regulated output designed to drive high current white LEDs
used in camera flash applications. The maximum flash
current is set by an external resistor, RSET, which sets the
flash current and the maximum movie-mode current.
The maximum movie-mode current is equal to the maximum programmed flash current minus the programmed
flash-to-movie-mode ratio whose default value is 7.3.
A flash pulse is initiated by strobing the FLEN input pin
low-to-high, which initiates a flash pulse and also starts
the internal timer. The maximum flash current in the
AAT1272 is set by an external resistor, RSET, which sets
the flash current and the maximum movie-mode current
reduced by a factor of 2. The flash timer will terminate
the flash current regardless of the status of the FLEN pin.
This can be either used as a simple flash timing pulse or
can be used as a safety timer in the event of a control
logic malfunction to prevent the LED from over-heating.
The maximum flash time is determined by an external
timing capacitor connected to the CT pin. The flash duration can be set from 50ms up to a maximum of 1s. The
10
I2C-compliant interface allows further adjustment of the
flash timer duration. This allows the flash timer duration
to be reduced in 16 linear steps from the maximum time
set by the timing capacitor. If the safety timer is not
needed in the application, it can be disabled by connecting the CT pin directly to AGND.
The AAT1272 has two LED current sources which share
the output current equally. For a single white LED application, the two current sources can be connected together to apply full output current into the LED. In two LED
applications, each diode can be connected to its corresponding current source (FLOUTA or FLOUTB) and the
output current will be shared. In applications where only
one LED is connected to either FLOUTA or FLOUTB, the
unused current sink must be directly connected to OUT,
thereby disabling that channel.
Movie Mode
The movie mode current level, the flash safety timer,
the output channel enable, and the flash-to-movie mode
current ratio can be set using the AAT1272’s I2Ccompliant interface. The movie-mode current level can
be adjusted in 16 steps using a logarithmic scale where
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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DATA SHEET
AAT1272
1.5A Step-Up Current Regulator for Flash LEDs
each code is 1dB below the previous code. The flash
safety delay can be reduced from the maximum value
programmed externally by CT in 16 linear steps. The
flash current outputs FLOUTA and FLOUTB can be
enabled or disabled individually or together. The flashto-movie-mode current ratio can be set from 1:2 to
1:30 with respect to the maximum programmed flash
current. The FLEN signal takes priority over movie-mode
operation. Lastly, the EN pin must be toggled low-tohigh to enable the AAT1272 to accept I2C programming
instructions.
Over-Temperature Protection
Thermal protection disables the AAT1272 when internal
power dissipation becomes excessive, as it disables both
MOSFETs. The junction over-temperature threshold is
140°C with 15°C of temperature hysteresis. The output
voltage automatically recovers when the over-temperature fault condition is removed.
Over-Voltage Protection
(Open LED, Open Circuit)
The AAT1272’s output voltage is limited by internal overvoltage protection circuitry, which prevents damage to
the AAT1272 from open LED or open circuit conditions.
During an open circuit, the output voltage rises and
reaches 5.5V (typical), and the OVP circuit disables the
switching, preventing the output voltage from rising
higher. Once the open circuit condition is removed,
switching will resume. The controller will return to normal operation and maintain an average output voltage.
Auto-Disable Feature
The AAT1272 is equipped with an auto-disable feature
for each LED channel. After the IC is enabled and started
up, a test current of 2-3mA (typical) is forced through
each sink channel. The channel will be disabled if the
voltage of that particular SINK pin does not drop to a
certain threshold. This feature is very convenient for
disabling an unused channel or during an LED fail-short
event. This small test current should be added to the set
output current in both Flash and MM conditions.
Applications Information
LED Selection
The AAT1272 is specifically designed to drive white flash
LEDs (typical forward voltage of 2.5V to 4.0V). Since the
FLOUTA and FLOUTB input current sinks are matched
with low voltage dependence; the LED-to-LED brightness
will be matched regardless of the individual LED forward
voltage (VF) levels.
Flash Mode LED Current
The LED current is controlled by the RSET resistor. For
maximum accuracy, a 1% tolerance resistor is recommended. FLOUTA and FLOUTB can be programmed up to
a maximum total flash current of 1.5A or up to 750mA
per channel. FLOUTA and FLOUTB output current is
matched across the programming range. A flash event is
initiated by asserting the FLEN pin. A flash event is automatically terminated when FLEN is disabled or if the
safety timer terminates before the FLEN pin is disabled.
The maximum flash current in each FLOUTA and FLOUTB
is set by the RSET resistor and can be calculated using the
following equation:
IFLOUTA = IFLOUTB =
81kΩ · A 81kΩ · A
=
= ~750mA per channel
RSET
107kΩ
To prevent excessive power dissipation during higher
flash current operation, RSET values smaller than 107kΩ
are not recommended.
Movie Mode LED Current
The maximum movie-mode current level is set by the
maximum, programmed flash current reduced by the
programmed flash-to-movie-mode ratio in which the
default value is 7.3:
IMOVIE-MODE[A/B] =
IFLOUT[A/B](MAX)
750mA
=
= 103mA
7.3
7.3
To change the configuration or the settings, the AAT1272
can be programmed via the I2C interface. Triggering the
FLEN low to high will enable a flash event with the maximum flash current set by the RSET resistor or with programmed flash current set via the I2C interface.
Concurrently, the flash timer is also initiated. All data
and register contents are cleared (reset to the default
value) after each flash event.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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11
DATA SHEET
AAT1272
1.5A Step-Up Current Regulator for Flash LEDs
Flash Safety Timeout
The AAT1272 includes a timer circuit that enables the
flash current for a programmed period of time. This feature eliminates the need for an external, housekeeping
baseband controller to contain a safety delay routine. It
also serves as a protection feature to minimize thermal
issues with the flash LEDs in the event an external controller’s flash software routine experiences hang-up or
freeze. The flash safety timeout, T can be calculated by
the following equation:
T = 7.98s/μF · CT
Where T is in seconds and CT is the capacitance of the
timer capacitor in μF.
For example, using a 47nF capacitor for CT sets the flash
timeout to:
Flash Safety Timeout = 7.98s/μF · 0.047μF = 375ms
The relationship between the flash safety timeout and
the capacitance of the timer capacitor is illustrated in
Figure 1.
Flash Timeout (ms)
1000
800
600
400
200
20
40
60
80
100
120
START and STOP conditions are always generated by the
master. Prior to initiating a START, both the SDA and SCL
pins are in idle mode (idle mode is when there is no
activity on the bus and SDA and SCL are pulled high by
the external pull-up resistors). A START condition occurs
when the master strobes the SDA line low and after a
short period strobes the SCL line low. A START condition
acts as a signal to all ICs that transmission activity is
about to occur on the I2C bus. A STOP condition, as
shown in Figure 2, is when master releases the bus and
SCL changes from low to high followed by SDA low-tohigh transition. The master does not issue an
ACKNOWLEDGE and releases the SCL and SDA pins.
I2C Address Bit Map
140
CT Capacitor (nF)
Figure 1: Flash Safety Timeout
vs. Timer Capacitor.
I2C Serial Interface
The AAT1272 is fully compliant with the industry-standard I2C interface. The I2C two-wire communications bus
consists of SDA and SCL lines. SDA provides data, while
SCL provides clock synchronization with speed up to
400kHz. SDA data transfers device address followed by
a register address and data bits sequence. When using
the I2C interface, EN is pulled high to enable the device
or low to disable the device. The I2C serial interface
12
I2C START and STOP Conditions
Figure 4 illustrates the address bit transfer. The 7-bit
address is transferred 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 on the eighth bit determines the direction of
the transfer (a '1' for read or a '0' for write). The
AAT1272 is a write-only device and the R/W bit must be
set low. The Acknowledge bit (ACK) is set to low by the
AAT1272 to acknowledge receipt of the address.
1200
0
0
requires a master to initiate all the communications with
target devices. The AAT1272 is a target device and only
supports the write protocol. The AAT1272 is manufactured with a target device address of 0x37 (Hex). See
Figure 2 for the I2C interface diagram.
I2C Register Address/Data Bit Map
Figure 5 illustrates the Register Address or the serial data
bit transfer. The 8-bit data is always transferred most
significant bit first and is valid when SCL is high. The
Acknowledge bit (ACK) is set low by the AAT1272 to
acknowledge receipt of the register address or the data.
I2C Acknowledge Bit (ACK)
The Acknowledge bit is the ninth bit of each transfer on
the SDA line. It is used to send back a confirmation to
the master that the data has been received properly by
the target device. For each ACK to take place, the master must first release the SDA line, and then the target
device will pull the SDA line low, as shown in Figures 1,
4, and 5.
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DATA SHEET
AAT1272
1.5A Step-Up Current Regulator for Flash LEDs
ack from slave
start
MSB
Device Address
LSB
w
ack
ack from slave
MSB
Register Address
LSB
ack
ack from slave
MSB
DATA
LSB
ack
stop
SCL
SDA
start
AAT1272 Device Address = 37h
w
ack
Register Address = 00h
Data = 06h
ack
ack
stop
Figure 2: I2C Interface Diagram.
STOP
START
SDA
SDA
SCL
SCL
Figure 3: I2C STOP and START 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
3
4
5
6
7
MSB
SDA
A6
8
9
LSB
A5
A4
A3
A2
A1
A0
R/W
ACK
Device Address
Figure 4: I2C Address Bit Map;
7-bit Slave Address (A6-A0), 1-bit Read/Write (R/W), 1-bit Acknowledge (ACK).
SCL
1
2
3
4
5
6
7
MSB
SDA
D7
8
9
LSB
D6
D5
D4
D3
D2
D1
D0
ACK
Register Address /
Data
Figure 5: I2C Register Address and Data Bit Map;
8-bit Data (D7-D0), 1-bit Acknowledge (ACK).
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DATA SHEET
AAT1272
1.5A Step-Up Current Regulator for Flash LEDs
Device Register Information
To program the register through the I2C interface, the master needs to send the AAT1272’s device address, 0x37 (Hex),
first, and then sends an 8-bit register address and 8-bit data. The AAT1272 has two registers, Register 0 and Register
1. If no instruction is written to the register, the default value is applied.
Register 0 (REG0), Register Address: 00h
Bits [7:4] Program the movie-mode current with 16 different percentage levels.
Bits [3:0] Program the flash safety timeout with 16 different fractions from the hardware configuration, CT.
MSB
7
LSB
6
5
4
3
2
1
0
Flash Safety
Timeout
0000 = 16/16 (default)
0001 = 15/16
0010 = 14/16
0011 = 13/16
0100 = 12/16
0101 = 11/16
0110 = 10/16
0111 = 9/16
1000 = 8/16
1001 = 7/16
1010 = 6/16
1011 = 5/16
1100 = 4/16
1101 = 3/16
1110 = 2/16
1111 = 1/16
Movie Mode
Current
0000 = 100% (default)
0001 = 89.1%
0010 = 79.4%
0011 = 70.8%
0100 = 63.1%
0101 = 56.2%
0110 = 50.1%
0111 = 44.7%
1000 = 39.8%
1001 = 35.5%
1010 = 31.6%
1011 = 28.2%
1100 = 25.1%
1101 = 22.4%
1110 = 20%
1111 = 0%
Figure 6: AAT1272 Register 0 Programming.
14
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DATA SHEET
AAT1272
1.5A Step-Up Current Regulator for Flash LEDs
Register 1 (REG1); Register Address: 01h
Bits [5:4] Program the FLOUTA and FLOUTB with four ON/OFF configurations.
Bits [3:0] Program the flash-to-movie mode ratio with 16 different fractions from the hardware configuration, RSET.
MSB
X
LSB
X
5
4
3
2
1
0
Flash-to-Movie
Mode Ratio
0000 = 1/2
0001 = 1/3.8
0010 = 1/5.5
0011 = 1/7.3 (default)
0100 = 1/8.9
0101 = 1/10.5
0110 = 1/12.2
0111 = 1/13.8
1000 = 1/14.9
1001 = 1/16.5
1010 = 1/18
1011 = 1/19.6
1100 = 1/21.1
1101 = 1/22.6
1110 = 1/24
1111 = OFF
00
01
10
11
FLOUTA FLOUTB
OFF
OFF (default)
OFF*
ON
ON
OFF*
ON
ON
*with 2-3mA standby current
Figure 7: AAT1272 Register 1 Programming.
Selecting the Boost Inductor
The AAT1272 controller utilizes PWM control and the
switching frequency is fixed. To maintain 2MHz maximum
switching frequency and stable operation, a 1μH inductor
is recommended. Manufacturer’s specifications list both
the inductor DC current rating, which is a thermal limitation, and peak inductor current rating, which is determined by the saturation characteristics. Measurements
at full load and high ambient temperature should be performed to ensure that the inductor does not saturate or
exhibit excessive temperature rise.
The inductor (L) is selected to avoid saturation at minimum input voltage and maximum output load conditions.
Worst-case peak current occurs at minimum input voltage (maximum duty cycle) and maximum load. Bench
measurements are recommended to confirm actual IPEAK
and to ensure that the inductor does not saturate at
maximum LED current and minimum input supply voltage. The RMS current flowing through the boost inductor
is equal to the DC plus AC ripple components. Under
worst case RMS conditions, the current waveform is
critically continuous. The resulting RMS calculation yields
worst case inductor loss. The RMS current value should
be compared against the inductor manufacturer’s temperature rise, or thermal derating guidelines:
IRMS =
IPEAK
3
For a given inductor type, smaller inductor size leads to
an increase in DCR winding resistance and, in most
cases, increased thermal impedance. Winding resistance
degrades boost converter efficiency and increases the
inductor’s operating temperature:
PLOSS(INDUCTOR) = I2RMS · DCR
*Denotes the default value.
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15
DATA SHEET
AAT1272
1.5A Step-Up Current Regulator for Flash LEDs
Selecting the Boost Capacitors
In general, it is good design practice to place a decoupling capacitor (input capacitor) between the IN and GND
pins. An input capacitor in the range of 2.2μF to 10μF is
recommended. A larger input capacitor in this application
may be required for stability, transient response, and/or
ripple performance. The high output ripple inherent in
the boost converter necessitates the use of low impedance output filtering. Multi-layer ceramic (MLC) capacitors provide small size and adequate capacitance, low
parasitic equivalent series resistance (ESR) and equivalent series inductance (ESL), and are well suited for use
with the AAT1272 boost regulator. MLC capacitors of type
X7R or X5R are recommended to ensure good capacitance stability over the full operating temperature range.
The output capacitor is selected to maintain the output
load without significant voltage droop (∆VOUT) during the
power switch ON interval. A 2.2μF ceramic output capacitor is recommended (see Table 7). Typically, 6.3V or 10V
rated capacitors are required for this flash LED boost
output. Ceramic capacitors selected as small as 0603 are
available which meet these requirements. MLC capacitors
exhibit significant capacitance reduction with applied
voltage. Output ripple measurements should confirm
that output voltage droop and operating stability are
within acceptable limits. Voltage derating can minimize
this factor, but results may vary with package size and
among specific manufacturers. To maintain stable operation at full load, the output capacitor should be selected
to maintain ∆VOUT between 100mV and 200mV. The boost
converter input current flows during both ON and OFF
switching intervals. The input ripple current is less than
the output ripple and, as a result, less input capacitance
is required.
PCB Layout Guidelines
Boost converter performance can be adversely affected
by poor layout. Possible impact includes high input and
output voltage ripple, poor EMI performance, and
reduced operating efficiency. Every attempt should be
made to optimize the layout in order to minimize parasitic PCB effects (stray resistance, capacitance, and
inductance) and EMI coupling from the high frequency
SW node. A suggested PCB layout for the AAT1272 1.5A
step-up regulator is shown in Figures 4 and 5. The following PCB layout guidelines should be considered:
1.
2.
3.
4.
5.
Minimize the distance from capacitor CIN and COUT’s
negative terminals to the PGND pins. This is especially true with output capacitor COUT, which conducts
high ripple current from the output to the PGND pins.
Minimize the distance under the inductor between IN
and switching pin SW; minimize the size of the PCB
area connected to the SW pin.
Maintain a ground plane and connect to the IC PGND
pin(s) as well as the PGND connections of CIN and
COUT.
Consider additional PCB exposed area for the flash
LEDs to maximize heatsinking capability. This may
be necessary when using high current application
and long flash duration application.
Connect the exposed paddle (bottom of the die) to
either PGND or GND. Connect AGND, FLGND to GND
as close as possible to the package.
Manufacturer
Part Number
Inductance
(μH)
Saturated Rated
Current (A)
DCR
(mΩ)
Size (mm)
LxWxH
Cooper Bussmann
Cooper Bussmann
Cooper Bussmann
Sumida
Coilcraft
SD3812-1R0-R
SDH3812-1R0-R
SD10-1R0-R
CDH38D11/S
LPS4012-102NLC
1
1
1
1
1
2.69
3
2.25
2.8
2.5
48
45
44.8
48.8
60
4.0x4.0x1.2
3.8x3.8x1.2
5.2x5.2x1.0
4.0x4.0x1.2
4.1x4.1x1.2
Type
Shielded
Shielded
Shielded
Shielded
Shielded
Drum
Drum
Drum
Drum
Drum
Core
Core
Core
Core
Core
Table 6: Typical Suggested Surface Mount Inductors.
Manufacturer
Murata
Part Number
Capacitance (μF)
Voltage Rating (V)
Temp Co.
Case Size
GRM185R60J225KE26
GRM188R71A225KE15
GRM21BR70J225KA01
GRM21BR71A225KA01
GRM219R61A475KE19
2.2
2.2
2.2
2.2
4.7
6.3
10
6.3
10
10
X5R
X7R
X7R
X7R
X5R
0603
0603
0805
0805
0805
GRM21BR71A106KE51
10
10
X7R
0805
Table 7: Typical Suggested Surface Mount Capacitors.
16
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DATA SHEET
AAT1272
1.5A Step-Up Current Regulator for Flash LEDs
SCL
VOUT
SDA
FLEN
JP1
0
R2
JP2
0
10k
VCC
D1
Enable
D2
U1
1
2
3
JP3
4
5
6
L1
1μH
C1
2.2μF
7
CT
EN
FLEN
AGND
IN
SW
PGND
14
RSET
FLA
FLGND
FLB
SDA
SCL
OUT
13
12
11
10
9
8
AAT1272 TDFN33-14
C3
74nF
R1
107k
L1
C1, C2
C3
D1, D2
C2
2.2μF
Cooper Bussmann SD3812-1R0-R, 1μH, 2.69A, 48mΩ
Murata GRM188R71A225KE15, 2.2μF, 0603, X7R, 10V
Murata GRM155R71A743KA01, 74nF, 0402, X7R, 10V
Lumiled LXCL-PWF4 or equivalent
Figure 8: AAT1272 Evaluation Board Schematic.
DC -
DC +
VCC
JP7
MCU
JP8
0
R5 R6 R7
10K 10K 10K
1
Movie Mode Control
Safety Timer
A / B Control
0
0
0
2
SW 1
3
21
43
5
4
SW 2
VDD
GP5
GP4
GP3
VSS
GP0
GP1
GP2
R8
10 k
C4
1μF
U2
8
FLEN
7
6
5
R4
330
PIC12F675
0
R3
330
21
43
5
LED 1
RED
21
43
5
LED 2
GRN
SW 3
SW4
JP4
R9
100k
21
43
5
R10
10k
R11
10k
SCL
JP5
FLEN
SDA
JP6
SCL
SDA
Figure 9: AAT1272 Evaluation Board MCU Section Schematic.
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DATA SHEET
AAT1272
1.5A Step-Up Current Regulator for Flash LEDs
Figure 10: AAT1272 Evaluation Board
Top Side Layout.
Component
Part Number
U1
AAT1272IWO
U2
SW1 – SW3
R1
R2, R9
R5 - R8, R10, R11
R3, R4
JP1, JP2, JP8
C1, C2
C3
C4
L1
D1-D2
LED1
LED2
JP3, JP4, JP5, JP6, JP7
PIC12F675
PTS645TL50
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
GRM188R71A225KE15
GRM155R71A743KA01
GRM216R61A105KA01
SD3812-1R0-R
LXCL-PWF4
CMD15-21SRC/TR8
CMD15-21VGC/TR8
PRPN401PAEN
Figure 11: AAT1272 Evaluation Board
Bottom Side Layout.
Description
1.5A Step-Up Current Regulator for Flash LEDs;
TDFN33-14 package
8-bit CMOS, FLASH-based μC; 8-pin PDIP package
Switch, SPST, 5mm
107kΩ, 1%, 1/4W; 0402
100kΩ, 1%, 1/4W; 0603
10kΩ, 5%, 1/4W; 0603
330Ω, 5%, 1/4W; 0603
0Ω, 5%
2.2μF, 10V, X7R, 0603
74nF, 10V, X7R, 0402
1μF, 10V, X5R, 0805
Drum Core, 1μH, 2.69A, 48mΩ
White Flash LED
Red LED; 1206
Green LED; 1206
Conn. Header, 2mm zip
Manufacturer
Skyworks
Microchip
ITT Industries
Vishay
Vishay
Vishay
Vishay
Vishay
Murata
Murata
Murata
Cooper Bussmann
Lumileds, Philips
Chicago Miniature Lamp
Chicago Miniature Lamp
Sullins Electronics
Table 8: AAT1272 Evaluation Board Bill of Materials.
18
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DATA SHEET
AAT1272
1.5A Step-Up Current Regulator for Flash LEDs
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
TDFN33-14
ZNXYY
AAT1272IWO-T1
Skyworks Green™ products are compliant with
all applicable legislation and are halogen-free.
For additional information, refer to Skyworks
Definition of Green™, document number
SQ04-0074.
Package Information
TDFN33-143
Detail "A"
3.000 ± 0.050
2.500 ± 0.050
Index Area
3.000 ± 0.050
1.650 ± 0.050
Top View
Bottom View
+ 0.100
- 0.000
Pin 1 Indicator
(Optional)
0.180 ± 0.050
Side View
0.400 BSC
0.000
0.203 REF
0.750 ± 0.050
0.425 ± 0.050
Detail "A"
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.
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19
DATA SHEET
AAT1272
1.5A Step-Up Current Regulator for Flash LEDs
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. Skyworks may change its documentation, products, services, specifications 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 conflicts, incompatibilities, or other difficulties 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 hereunder, 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, INCLUDING 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 environmental 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
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Customers are responsible for their products and applications using Skyworks products, which may deviate from published specifications as a result of design defects, errors, or operation of products outside of published parameters or design specifications. 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 specifications 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
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