AAT1277
DATA SHEET
1.5A Step-Up Current Regulator for Flash LEDs
1
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
General Description
The AAT1277 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.
The AAT1277 maintains output current regulation by
switching the internal high-side and low-side switch tran-
sistors. The transistor switches are pulse-width modu-
lated at a fixed frequency of 2MHz. The high switching
frequency allows the use of a small inductor and output
capacitor, making the AAT1277 ideally suited for small
battery-powered applications.
Three simple logic control inputs enable and disable flash
and movie mode operation of the AAT1277. Movie-mode
and Flash-mode current levels are independently fixed
by two separate resistors. For Flash mode, a default
timer can be used either to terminate a flash event or as
a safety feature. Also included is a Flash Inhibit pin
which reduces the flash current to movie-mode levels
during high battery demand. One or two LEDs can be
connected to the AAT1277; in the case of two LEDs the
output current is matched between each diode.
The AAT1277 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 1.0A.
The AAT1277 is available in a 18 ball 1.5mm x 2.4mm
CSP package.
Features
• V
IN 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 (1H)
• 2 MHz Switching Frequency
• Separate Flash/Movie Mode Enable
• Separate Flash Inhibit
• User-Programmable Safety Timer
• Two Resistors Set Flash and Movie Mode Current
Independently
• True Load Disconnect
• Bypass Mode Input Current Limit 1.9A (typ.)
• Over-Voltage (Open LED, Open Circuit) Protection
• Short Circuit Protection
• Over-Temperature Protection
• Shutdown Current < 1.0A
• 18 Ball 1.5mm x 2.4mm CSP Package
• -40°C to +85°C Operating Temperature Range
Applications
• Cellphones/Smartphones
• LED Photo Flash/Torch
• Mobile Handsets
Typical Application
RFSET 56.2kΩ
VBAT CIN
2.2µF
CT
47nF
L1 1µH
IN SW
OUT
FLOUTA
CT
MEN
FLINH
FSET
AGND PGND
FLEN
Movie Mode Enable
Flash Enable
Flash Inhibit
FLOUTB
FLGND
COUT
2.2µF
Flash LEDs
RMSET 169kΩ
MSET
AAT1277
AAT1277
DATA SHEET
1.5A Step-Up Current Regulator for Flash LEDs
2Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
Pin Descriptions
Ball # Symbol Function
A1 CT
Flash timer control input. Connect a capacitor between CT and AGND to set maximum duration of the fl ash
pulse. A 47nF ceramic capacitor sets the fl ash timer to 375ms. To disable the fl ash timer, connect CT to
AGND.
A2 MEN Movie mode enable pin. A low to high transition on the MEN pin initiates movie mode current level set by
MSET resistor. MEN is an active high control input with a internal 200k resistor to AGND.
A3 FLEN Flash enable pin. A low-to-high transition on the FLEN pin initiates a fl ash pulse and starts the fl ash timer.
FLEN is an active high control input with a internal 200k resistor to AGND.
A4 AGND Analog ground pin. Connect AGND to PGND and FLGND at a single point as close to AAT1277 as possible.
A5 IN Power input. Connect IN to the input power supply voltage. Connect a 2.2F or larger ceramic capacitor
from IN to PGND as close as possible to AAT1277.
A6, B3, B4 PGND Power ground pin. Connect PGND to AGND and FLGND at a single point as close to AAT1277 as possible.
B1 FSET
Flash mode current setting input. A 56.2k resistor from FSET to AGND sets the maximum fl ash current
available at FLOUTA and FLOUTB up to 1.5A total. Each FLOUTA and FLOUTB channel will conduct 50% of
the maximum programmed current
B2, C2 FLGND Flash ground pin. Connect FLGND to PGND and AGND at a single point as close to AAT1277 as possible
B5, B6 SW Boost converter switching node. Connect a 1H inductor between SW and IN.
C1 FLOUTA Flash Output A. Connect cathode of Flash LEDA to FLOUTA. For a single fl ash LED, connect FLOUTA and
FLOUTB together. For two fl ash LEDs, each output will conduct 50% of the total fl ash output current.
C3 FLOUTB Flash Output B. Connect cathode of Flash LEDB to FLOUTB. For a single fl ash LED, connect FLOUTB &
FLOUTA together. For two fl ash LEDs, each output will conduct 50% of the total fl ash output current.
C4 FLINH
Flash inhibit pin. FLINH is an active high control input with an internal 200k resistor to AGND. A low-to-
high transition on the FLINH pin reduces FLOUTA and FLOUTB output currents to the preset movie-mode
current level for the duration of FLINH. Strobing the FLINH pin low to high does not reset the fl ash timer.
C5 MSET
Movie mode current setting input. A 169k resistor from MSET to AGND sets the desired movie mode
current available at FLOUTA and FLOUTB to 100mA total. Each FLOUTA and FLOUTB channel will conduct
50% of the programmed current.
C6 OUT Power output of the boost converter. Connect a 2.2F or larger ceramic capacitor from OUT to PGND as
close as possible to the AAT1277. Connect OUT to the anode(s) of the Flash LED(s).
Pin Configuration
CSP Ball/Pin Layout
(Top View)
A3 B3 C3
A5 B5 C5
A1 B1 C1
A4 B4 C4
A2 B2 C2
A6 B6 C6
6
5
4
3
2
1
ABC
AAT1277
DATA SHEET
1.5A Step-Up Current Regulator for Flash LEDs
3
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
Absolute Maximum Ratings1
(TA = 25°C unless otherwise noted.)
Symbol Description Value Units
IN, SW, OUT Maximum Rating -0.3 to 6.0
VMEN, FLEN, FLINH, CT, MSET, FSET Maximum Rating VIN + 0.3
FLOUTA, FLOUTB Maximum Rating VOUT + 0.3
TJJunction Temperature Range -40 to 150
C
TAOperating Temperature Range -40 to 85
TsStorage Temperature Range -65 to 150
TLEAD Maximum Soldering Temperature (at leads, 10 sec.) 300
Thermal Information2
Symbol Description Value Units
JA Thermal Resistance 105.5 C/W
PDMaximum Power Dissipation3940 mW
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.
2. Mounted on an FR4 board.
3. Derate 9.4 mW above 25°C.
AAT1277
DATA SHEET
1.5A Step-Up Current Regulator for Flash LEDs
4Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
Electrical Characteristics1
VIN = 3.6V; CIN = COUT = 2.2F; L1 = 1H; RFSET = 56.2k; RMSET = 169k; TA = -40°C to 85°C unless otherwise noted.
Typical values are at TA = 25°C.
Symbol Description Conditions Min Typ Max Units
Power Supply
VIN Input Voltage Range 2.7 5.5 V
VOUT(MAX) Maximum Output Voltage 5.5
IIN(Q) VIN Supply Current VFLEN = VIN, FL Load = 1.5A 1.4 mA
VFLEN = VIN, FL Load = 0A 0.23
ISHDN(MAX) VIN Shutdown Current VMEN = VFLEN = VFLINH = GND 1 A
IFL(TOTAL) Total Output Current, Flash Mode IFLOUTA + IFLOUTB 1.2 1.5 A
IFL FLOUTA / FLOUTB Current Accuracy -5 5 %
IFL(MATCH) FLOUTA / FLOUTB Current Matching Tolerance 10 %
IMM(LOAD) Total Output Current, Movie Mode IMMOUTA + IMMOUTB 93 100 107 mA
fOSC Oscillator Switching Frequency TA = 25°C 1.45 2.0 2.55 MHz
tDEFAULT Default ON Time CT = 47nF 375 ms
TSD Thermal Shutdown Threshold 140 °C
TSD(HYS) Thermal Shutdown Hysteresis 15
FLEN/ MEN/FLINH Logic Control
VMEN(L),
VFLEN(L),
VFLINH(L)
MEN, FLEN, FLINH Input Low Threshold 0.4 V
VMEN(H),
VFLEN(H),
VFLINH(H)
MEN, FLEN, FLINH Input High Threshold 1.4 V
RIN(LOGIC) FLINH, FLEN, MEN Input Resistance to AGND 100 200 k
tFLEN_ON FLEN ON Delay Time 200
s
tFLEN_OFF FLEN OFF Delay Time 10
tFLINH_ON FLINH ON Delay Time 93
tFLINH_OFF FLINH OFF Delay Time 5
Auto Disable Function2
VLED(DETECT) Shorted LED Detection Voltage VIN = 3V, ILED = 0.795A 1.45 V
ILED(DETECT) Minimum LED Detection Current VIN = 3V 795 A
1. The AAT1277 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.
2. Guranteed by Design
AAT1277
DATA SHEET
1.5A Step-Up Current Regulator for Flash LEDs
5
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
AAT1277
1.5A Step-Up Current Regulator for Flash LEDs
SwitchRegTM
PRODUCT DATASHEET
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
40
50
60
70
80
90
100
320mA, V
F
= 2.91V
540mA, V
F
= 3.00V
700mA, V
F
= 3.04V
900mA, V
F
= 3.04V
1500mA, V
F
= 3.15V
1200mA, V
F
= 3.27V
Flash Mode Efficiency vs. Input Voltage
Input Voltage (V)
Efficiency (%)
Movie Mode Efficiency vs. Input Voltage
Input Voltage (V)
Efficiency (%)
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
50
55
60
65
70
75
80
85
90 204mA
104mA
52mA
Shutdown Current vs. Input Voltage
(VMEN = VFLEN = VFLINH = 0V)
Input Voltage (V)
Shutdown Current (μA)
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
0
0.005
0.01
0.015
0.02
0.025
0.03
25°C
-40°C
0
50
100
150
200
250
300
350
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
85C
25C
-40C
Quiescient Current vs. Input Voltage
( VFLEN = VIN; IFLOUTA = IFLOUTB = 0mA)
Input Voltage (V)
IIN(Q) (µA)
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
-40 -15 10 35 60 85
FL1
FL2
Movie Mode Current Accuracy vs. Temperature
(VIN = 3.6V; IFLOUTA = IFLOUTB = 50mA)
Temperature (°C)
Output Current Accuracy (%)
-0.2
0
0.2
0.4
0.6
0.8
-0.8
-0.6
-0.4
-40 -15 10 35 60 85
Movie Mode
Flash Mode
Flash and Movie Modes Current Matching
vs. Temperature
(VIN = 3.6V)
Tem
p
erature
(
°C
)
Output Current Accuracy (%)
AAT1277
DATA SHEET
1.5A Step-Up Current Regulator for Flash LEDs
6Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
AAT1277
1.5A Step-Up Current Regulator for Flash LEDs
SwitchRegTM
PRODUCT DATASHEET
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
FL1
FL2
-40 -15 10 35 60 85
Flash LED Current Accuracy vs. Temperature
(VIN= 3.6V; IFLOUTA= IFLOUTB= 750mA)
Temperature (C)
Output Current Accuracy (%)
0
40
80
120
160
200
240
320
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
85C
25C
-40C
280
Flash ON Delay Time vs. Input Voltage
(IFLOUTA = IFLOUTB = 750mA; COUT = 2.2μF; L = 1μH)
Input Voltage (V)
Flash ON Delay Time (μs)
280
300
320
340
360
380
400
420
440
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
85C
25C
-40C
Flash ON Time vs. Input Voltage
(IFLOUTA = IFLOUTB = 750mA; CT = 47nF; COUT = 2.2μF; L = 1μH)
Input Voltage (V)
Flash ON Time (ms)
Flash Timeout Delay vs. CT Capacitor
(IFLOUTA = IFLOUTB = 750mA/ch; VIN = 3.6V)
CT Capacitor (nF)
Flash Timeout (ms)
0 20 40 60 80 100 120 140
0
200
400
600
800
1000
1200
0
2
4
6
8
10
-10
-8
-6
-4
-2
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
Movie Mode Current Accuracy vs. Input Voltage
(IFLOUTA = IFLOUTB = 50mA; COUT = 2.2μF; L = 1μH)
Input Voltage (V)
Movie Mode LED Accuracy (%)
-4
-3
-2
-1
0
1
2
3
4
-40 -15 10 35 60 85
Oscillator Frequency Accuracy vs. Temperature
(VIN = 3.6V; FOSC = 2MHz)
Temperature (°C)
Oscillator Frequency Accuracy (%)
AAT1277
DATA SHEET
1.5A Step-Up Current Regulator for Flash LEDs
7
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
AAT1277
1.5A Step-Up Current Regulator for Flash LEDs
SwitchRegTM
PRODUCT DATASHEET
1.6
1.7
1.8
1.9
2
2.1
2.2
2.3
2.4
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
Oscillator Frequency vs. Input Voltage
(TA = 25°C)
Input Voltage (V)
Oscillator Frequency (MHz)
Flash Mode Output Ripple
(IFLOUT = 1.5A; VIN = 4V; L = 1μH)
Time (200ns/div)
VOUT
(AC Coupled)
(50mV/div)
IINDUCTOR
(50mA/div)
VINDUCTOR
(2V/div)
1.65A
0V
Movie Mode Line Transient
(IFLOUT = 206mA; VIN = 4.2V to 3.6V)
Time (50μs/div)
IFL
(AC Coupled)
(50mA/div)
VIN
(500mV/div)
4.2V
3.6V
0V
0V
VMEN
5V/div
0V
VOUT
2V/div
VFLx
2V/div
IFLx
100mA/div
0A
Movie Mode Turn On Characteristic
(IFLOUTA = IFLOUTB = 50mA; COUT = 2.2μF; VIN = 3.6V; L= 1μH)
Time (100μs/div)
0A
VFLEN
5V/div
0V
VOUT
1V/div
3.0
VFLx
0V
1V/div
IFLx
1A/div
Movie Mode to Flash Turn On Characteristic
(IFLOUTA= IFLOUTB = 50mA to 750mA; COUT = 1.0uF; VIN = 3.6V; L= 1μH)
Time (100us/div)
VFLEN
5V/div
VOUT
2V/div
VFLx
2V/div
IFLx
1A/div
0V
0V
0V
0V
Flash Turn On Characteristic
(IFLOUTA = IFLOUTB = 750mA; COUT = 2.2μF; VIN = 3.6V; L = 1μH)
Time (100us/div)
AAT1277
DATA SHEET
1.5A Step-Up Current Regulator for Flash LEDs
8Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
AAT1277
1.5A Step-Up Current Regulator for Flash LEDs
SwitchRegTM
PRODUCT DATASHEET
VFLEN
5V/div
VOUT
1V/div
VFLx
1V/div
IFLx
1A/div
0A
0V
3.3
0V
Flash Inhibit Turn On Characteristic
(IFLOUTA = IFLOUTB = 750mA to 50mA; COUT = 2.2μF; VIN = 3.6V; L = 1μH)
Time (100us/div)
VFLEN
5V/div
VOUT
2V/div
VFLx
2V/div
IFLx
1A/div
0V
0V
0V
0V
Flash Mode Timing
(IFLOUTA = IFLOUTB = 750mA; COUT = 2.2μF; VIN = 3.6V; L = 1μH)
Time (100ms/div)
VOUT
20mV/div
AC Coupling
VSW
2V/div
ISW
200mA/div
0A
0V
Movie Mode Ripple
(IFLOUTA = IFLOUTB = 50mA; COUT = 2.2μF; VIN = 3.1V; L = 1μH)
Time (500ns/div)
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
25C
85C
-40C
MEN, FLEN, FLINH Logic Threshold
High vs Input Voltage
Input Voltage (V)
VMEN, VFLEN, VFLNH (V)
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
25C
85C
-40C
MEN, FLEN, FLINH Logic Threshold
Low vs Input Voltage
Input Voltage (V)
VMEN, VFLEN, VFLNH (V)
200
250
300
350
400
0
50
100
150
-40 -15 10 35 60 85
MEN, FLEN, FLINH Input Pull Down
Resistance vs Temperature
Temperature (°C)
RMEN, RFLEN, RFLNH (kΩ)
AAT1277
DATA SHEET
1.5A Step-Up Current Regulator for Flash LEDs
9
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
Functional Description
The AAT1277 is a boost converter with a current regu-
lated output designed to drive high current white LEDs
used in camera flash applications. The AAT1277 has two
channels to accurately regulate the current flow through
two separate white LEDs. There are two basic modes of
operation in the AAT1277; a Flash mode controlled by
the FLEN pin and movie mode controlled through the
MEN pin.
Flash Mode
By strobing the FLEN input pin low-to-high, a flash pulse
and the internal timer are initiated. The maximum flash
current in the AAT1277 is set by an external resistor,
RFSET
. 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 malfunc-
tion to prevent the LED from overheating.
The maximum flash time is determined by an external
timing capacitor connected to the CT pin. It is not recom-
mended for the flash duration to be set longer than 1s.
If the safety timer is not needed in the application, it can
be disabled by connecting the CT pin directly to AGND.
After a flash event has expired via the flash timer, both
MEN and FLEN must be cycled to a logic low state to
reset the flash timer.
The AAT1277 has two LED current sources which share
the output current equally. For a single white LED appli-
cation, the two current sources can be connected togeth-
er to apply full output current into the LED. In two LED
applications, each diode can be connected to its corre-
sponding 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.
Flash Inhibit Function
In mobile GSM systems where the phone remains in
constant contact with the base station by regular com-
munication, a FLINH pin is provided to prevent both the
camera flash and PA transmission pulses from occurring
simultaneously. This avoids potential dips to the Li-ion
battery voltage below the system’s undervoltage lockout
threshold (UVLO). During a flash event, strobing the
FLINH pin low-to-high reduces the LED current to the
default movie-mode current level for the duration of
FLINH. Strobing FLINH high-to-low instructs the AAT1277
to revert the flash LED current to its maximum level,
assuming that the FLEN pin is still active (HIGH) and the
flash timer has not expired.
Functional Block Diagram
SW
PGND
FLOUT
A
AGND
Control
FSET
IN
CT
FLOUTB
FLGND
OUT
MEN
MSET
FLEN
FLINH
AAT1277
DATA SHEET
1.5A Step-Up Current Regulator for Flash LEDs
10 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
Movie Mode
The movie mode is enabled when the MEN input pin
transitions from low to high and will remain on until input
is pulled back to a low logic level. The movie-mode cur-
rent level is set by an external resistor connected
between MSET and AGND. Channel current outputs
(FLOUTA and FLOUTB) in movie mode operate in the
same manner as they do in flash mode, only at a current
level as set by the RMSET resistor. The flash timer function
is disabled in movie mode to permit constant LED illumi-
nation.The FLEN signal takes priority over movie-mode
operation.
Over-Temperature Protection
Thermal protection disables the AAT1277 when internal
power dissipation becomes excessive when operating.
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 AAT1277’s output voltage is limited by internal over-
voltage protection (OVP) circuitry, which prevents dam-
age to the AAT1277 from open LED or open circuit condi-
tions. 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 and the controller will return to
normal operation.
Auto-Disable Feature
The AAT1277 is equipped with an auto-disable feature for
each LED channel. After the IC is enabled and started up,
a test current of 1mA (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 movie mode conditions.
Timing Diagrams
MEN
FLEN
IFLOUTA = IFLOUTB = IMM
t = 0 t = n
OFF
Figure 1: Movie Mode Timing Diagram.
AAT1277
DATA SHEET
1.5A Step-Up Current Regulator for Flash LEDs
11
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
t = 0 t = t
CT
MEN
FLEN
IFLOUTA = IFLOUTA = IFL
OFF
Figure 2: Diagram of Flash Mode When Flash Event Does Not Exceed Flash Timer TFLASH < TCT.
t = 0 t = t
CT
MEN
FLEN
OFF
IFLOUTA = IFLOUTA = IFL
Figure 3: Diagram of Flash Mode Timing When Flash Event is Terminated by Flash Timer TFLASH TCT.
t = 0 t = t CT
MEN
FLEN
MM=ON
OFF
IFLOUTA = IFLOUTA = IFL
IFLOUTA = IFLOUTA = IMM
Figure 4: Diagram of Movie Mode Followed by Flash Mode When
Flash Event is Terminated Before Flash Timer TFLASH < TCT1,2.
1. FLEN must be pulled low after a flash time out period to reset the flash timer.
2. Movie mode will not re-enable until FLEN returns low after flash time.
AAT1277
DATA SHEET
1.5A Step-Up Current Regulator for Flash LEDs
12 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
t = 0 t = t
CT
MEN
FLEN
IFLOUTA = IFLOUTA = IMM
MM = ON
OFF Flash
Timer
Reset
Next
Flash
Event
IFLOUTA = IFLOUTA = IFL
Figure 5: Diagram of Movie Mode Followed by Flash Mode
When Flash Event is Terminated by Flash Timer TFLASH < TCT.
(Note: Both MEN and FLEN must return to a logic low state to reset the flash timer
before the system can execute another flash or movie mode event.)
t = 0 t = t
CT
MEN
FLEN
MM=ON
OFF
FLINH
IFLOUTA = IFLOUTA = IFL
IFLOUTA = IFLOUTA = IMM
Figure 6: Diagram of Movie Mode Followed By Flash Mode
With Flash Inhibit During Flash Event TFLASH < TCT.
(Note: The flash current is reduced to the movie mode current for the duration of FLINH).
AAT1277
DATA SHEET
1.5A Step-Up Current Regulator for Flash LEDs
13
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
Applications Information
LED Selection
The AAT1277 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 Current
FLOUTA and FLOUTB can be programmed up to a maxi-
mum total flash current of 1.5A or up to 750mA per
channel. The output currents in FLOUTA and FLOUTB are
equal.
The maximum flash current in each FLOUTA and FLOUTB
is set by the RFSET resistor. For the desired flash current
in each output, the resistor value can be calculated using
the following equation:
56.2kΩ · 750mA
I
FLOUTX
R
FSET
=
A flash event is initiated by asserting the FLEN pin. A
flash event is automatically terminated when FLEN is de-
asserted or if the safety timer terminates before the
FLEN pin is de-asserted. Any time that the FLINH pin is
asserted, the default movie-mode current level will
appear at both FLOUTA and FLOUTB. The default movie-
mode current level will be maintained on FLOUTA and
FLOUTB as long as the FLINH and FLEN pins are assert-
ed, and the safety timer continues to run.
Movie Mode Current
The AAT1277 movie mode current settings can be pro-
grammed by the external resistor RMSET
.
169kΩ · 50mA
I
MMOUTX
R
MSET
=
Flash Timer
The AAT1277 flash timer function is programmed by an
external timing capacitor, CT
. The primary purpose of the
flash timer is a safety function to prevent damage to the
flash LED should a system error occur during a flash
event and fail to pull the FLEN input low after a flash
event. The flash timer may also be used to strobe the
flash relay in the timer to turn the flash off after a preset
time determined by the CT capacitor. This feature elimi-
nates the need for an external housekeeping baseband
controller to contain a safety or delay routine.
The flash time T can be calculated by the following equa-
tion:
T = 7.98s/μF · CT (μF)
Where T is in seconds and CT is in F.
For example, using a 47nF capacitor at CT sets the flash
timeout to:
Flash Timeout = 7.98s/μF · 47nF = 375ms
The relationship between the flash safety timeout and
the capacitance of the timer capacitor is illustrated in
Figure 7.
CT Capacitor (nF)
Flash Timeout (ms)
0 20 40 60 80 100 120 140
0
200
400
600
800
1000
1200
Figure 7: Flash Safety Timeout
vs. Timer Capacitor.
Shutdown
The current sink devices (FLOUTA and FLOUTB) are the
power returns for all loads, there si no leakage current
through load if the current sink devices are disabled.
When FLEN and MEN are both held at logic low level, the
AAT1277 is disabled and draws less than 1uA of leakage
current from VIN.
AAT1277
DATA SHEET
1.5A Step-Up Current Regulator for Flash LEDs
14 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
Selecting the Boost Inductor
The AAT1277 controller utilizes PWM control and the
switching frequency is fixed. To maintain 2MHz maximum
switching frequency and stable operation, a 1H inductor
is recommended. Manufacturer’s specifications list both
the inductor DC current rating, which is a thermal limita-
tion, and peak inductor current rating, which is deter-
mined by the saturation characteristics. Measurements
at full load and high ambient temperature should be per-
formed to ensure that the inductor does not saturate or
exhibit excessive temperature rise.
The inductor (L) is selected to avoid saturation at mini-
mum input voltage and maximum output load conditions.
Worst-case peak current occurs at minimum input volt-
age (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 volt-
age. 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 tem-
perature rise, or thermal derating guidelines:
IPEAK
3
RMS
I=
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:
P
LOSS(INDUCTOR)
= I
2RMS
· DCR
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 2.2F to 10F is recom-
mended. 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 equiv-
alent series resistance (ESR) and equivalent series induc-
tance (ESL), and are well suited for use with the AAT1277
boost regulator. MLC capacitors of type X7R or X5R are
recommended to ensure good capacitance stability over
the full operating temperature range. The output capaci-
tor is selected to maintain the output load without sig-
nificant voltage droop (VOUT) during the power switch ON
interval. A 1F ceramic output capacitor is recommended
(see Table 2). Typically, 6.3V or 10V rated capacitors are
required for this flash LED boost output. Ceramic capaci-
tors 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 drop
and operating stability are within acceptable limits.
Voltage derating can minimize this factor, but results may
vary with package size and among specific manufactur-
ers. 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 para-
sitic PCB effects (stray resistance, capacitance, and
inductance) and EMI coupling from the high frequency
SW node. A suggested PCB layout for the AAT1277 1.5A
step-up regulator is shown in Figures 4 and 5. The fol-
lowing PCB layout guidelines should be considered:
1. Minimize the distance from capacitor CIN and COUT’s
negative terminals to the PGND pins. This is espe-
cially true with output capacitor COUT
, which conducts
high ripple current from the output to the PGND
pins.
2. Minimize the distance under the inductor between IN
and switching pin SW; minimize the size of the PCB
area connected to the SW pin.
3. Maintain a ground plane and connect to the IC PGND
pin(s) as well as the PGND connections of CIN and
COUT
.
4. 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.
5. 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.
AAT1277
DATA SHEET
1.5A Step-Up Current Regulator for Flash LEDs
15
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
Manufacturer Part Number
Inductance
(H)
Saturated Rated
Current (A)
DCR
(m)
Size (mm)
LxWxH Type
Cooper Bussmann SD3812-1R0-R 1 2.69 48 4.0x4.0x1.2 Shielded Drum Core
Cooper Bussmann SDH3812-1R0-R 1 3 45 3.8x3.8x1.2 Shielded Drum Core
Cooper Bussmann SD10-1R0-R 1 2.25 44.8 5.2x5.2x1.0 Shielded Drum Core
Sumida CDH38D11/S 1 2.8 48.8 4.0x4.0x1.2 Shielded Drum Core
Coilcraft LPS4012-102NLC 1 2.5 60 4.1x4.1x1.2 Shielded Drum Core
Table 1: Typical Suggested Surface Mount Inductors.
Manufacturer Part Number Capacitance (F) Voltage Rating (V) Temp Co. Case Size
Murata
GRM185R60J225KE26 2.2 6.3 X5R 0603
GRM188R71A225KE15 2.2 10 X7R 0603
GRM21BR70J225KA01 2.2 6.3 X7R 0805
GRM21BR71A225KA01 2.2 10 X7R 0805
GRM219R61A475KE19 4.7 10 X5R 0805
GRM21BR71A106KE51 10 10 X7R 0805
Table 2: Typical Suggested Surface Mount Capacitors.
*Denotes the default value.
AAT1277
DATA SHEET
1.5A Step-Up Current Regulator for Flash LEDs
16 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
2.2µF
C2
2.2µF
C1
56.2k
R1
VOUT
0
JP1
0
JP2
47nF
C3
VIN
D1, D2 Seoul Semi FOW401-Z4S
L1 CooperBussmann SD3812-1R0-R, 1µH, 2.69A, 48mΩ
C1, C2 Murata GRM188R71A225KE15 2.2µF, 0603, X7R, 10V
C3 Murata GRM155R71A473KA01, 47nH, 0402, X7R, 10V
C4
1µF
169k
R2
GND
D1 D2
1
32
4
FLINH
SW1
1
32
4
FLEN
SW2
1
32
4
MEN
SW3
100k
R3
100k
R4
100k
R5
1µH
L1
IN
A5
CT
A1
SW
B5, B6
OUT C6
MEN
A2
FLEN
A3
PGND
A6, B3, B4
AGND
A4
MSET C5
FLINH C4
FLOUTB C3
FLGND B2, C2
FLOUTA C1
FSET B1
AAT1277 CSP-18
U1
J2
J1
J3
VIN
VIN
VIN
VIN
Figure 8: AAT1277 Evaluation Board Schematic.
Figure 9: AAT1277 Evaluation Board Figure 10: AAT1277 Evaluation Board
Top Side Layout. Bottom Side Layout.
AAT1277
DATA SHEET
1.5A Step-Up Current Regulator for Flash LEDs
17
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
Component Part Number Description Manufacturer
U1 AAT1277IUT 1.5A Step-Up Current Regulator for Flash LEDs;
18 ball 1.5mm x 2.4mm CSP package Skyworks
SW1 – SW3 PTS645TL50 Switch, SPST, 5mm ITT Industries
R1 Chip Resistor 56.2k, 1%, 1/4W; 0402 Vishay
R2 Chip Resistor 169k, 1%, 1/4W; 0402 Vishay
R3, R4, R5 Chip Resistor 100k, 1%, 1/4W; 0603 Vishay
JP1, JP2 Chip Resistor 0, 5%, 1/4W; 0603 Vishay
C1, C2 GRM188R71A225KE15 2.2F, 10V, X7R, 0603 Murata
C3 GRM155R71A473KA01 47nF, 10V, X7R, 0402 Murata
L1 SD3812-1R0-R Drum Core, 1H, 2.69A, 48mCooper Bussmann
D1-D2 LXCL-PWF4 White Flash LED Lumileds, Philips
Table 3: AAT1277 Evaluation Board Bill of Materials.
AAT1277
DATA SHEET
1.5A Step-Up Current Regulator for Flash LEDs
18 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
Ordering Information
Package Marking1Part Number (Tape and Reel)2
CSP-18 M6XYY AAT1277IUT-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
CSP-18
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.
AAT1277
DATA SHEET
1.5A Step-Up Current Regulator for Flash LEDs
19
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
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, specifi 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 confl icts, incompatibilities, or other diffi 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 specifi cations as a result of design defects, errors, or operation of products outside of pub-
lished parameters or design specifi 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 specifi 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
identifi 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.
