AAT1278
DATA SHEET
1.5A Single Flash LED Driver
1
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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General Description
The AAT1278 is a high-efficiency, 1.5A high-current
boost converter for LED photo flash applications. It
maintains output current regulation by switching the
internal high-side and low-side switch transistors, pulse-
width modulated at a fixed frequency of 2MHz. The high
switching frequency allows the use of a small external
inductor and output capacitor, making the AAT1278 ide-
ally suited in all single cell, Li-ion-powered applications.
Skyworks' proprietary AS2Cwire™ (Advanced Simple
Serial Control™) serial digital interface is used to enable,
disable, configure, and program the operation of the
AAT1278. Using the AS2Cwire interface, the movie-mode
current level for each LED, and the flash-to-movie-mode
current ratio can be programmed to one of 16 levels. The
AAT1278 includes a separate Flash Enable input to initi-
ate the flash operation and a Flash Inhibit pin which
reduces the flash current to movie-mode levels during
high battery demand.
The maximum flash and movie-mode current is set by
one external resistor where the ratio of flash to movie-
mode current is set at approximately 7.3:1. The AAT1278
can drive one high current LED.
The AAT1278 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 AAT1278 is available in a Pb-free, thermally-enhanced
CSP-12 package and operates over the -40°C to 85°C
temperature range.
Features
• Input Voltage Range: 2.7V to 5.5V
• Single Channel Flash Output
• Up to 1.5A Regulated Output Current
• Up to 88% Efficiency
• 2MHz Switching Frequency
• Separate Flash Enable
• Single Resistor Sets Flash and Movie Mode Current
AS2Cwire Single Wire Programming:
• Movie Mode Current
• Flash/Movie Mode Current Ratio
• True Load Disconnect
• Soft-Start and Input Current Limit
• Over-Voltage (Open LED, Open Circuit), Short Circuit,
and Over-Temperature Protection
• -40°C to +85°C Temperature Range
Applications
• LED Photo Flash / Torch
• Camera Enabled Mobile Devices
• Cellphones/Smartphones
• Digital Still Cameras (DSCs)
• Multimedia Mobile Phones
Typical Application
AAT1278
RSET
CIN
2.2μF
COUT
2.2μF
IN OUT
EN/SET
FLEN
AGNDPGND FLGND
RSET
Flash LED
Enable/Set Input
Flash Enable
FL
VBAT = 2.7V to 5.5V SW
L1 1μH
FLINH
Flash Inhibit
AAT1278
DATA SHEET
1.5A Single Flash LED Driver
2Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202088A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
Pin Descriptions
Pin # Symbol Description
A1 EN/SET Enable and Serial Control input. EN/SET is the AS2Cwire addressing and programming input to: a) adjust
the movie-mode current level; b) select the Flash-to-Movie-mode ratio.
A2 FLEN Flash enable pin. A low-to-high transition on the FLEN pin initiates a fl ash pulse and a high-to-low
transition on the FLEN pin terminates a fl ash pulse.
A3 AGND Analog ground pin. Connect AGND to PGND, and FLGND at a single point as close to the AAT1278 as
possible.
A4 PGND Power ground. Connect PGND to the same single point as AGND located as close to the AAT1278 as
possible.
B1 RSET Flash current set pin. Connect a resistor from RSET to AGND to program the desired fl ash current for the
current sink FL.
B2 IN
Flash output boost converter power input. Connect IN to the input power source. Connect a 2.2F or larger
ceramic capacitor from IN to PGND and locate as close as possible to the AAT1278 package for optimum
performance.
B3, B4 SW Boost converter switching node. Connect a 1H inductor between SW and IN.
C1 FL LED Flash current sink pin. Connect the cathode of Flash LED to FL.
C2 FLGND Flash ground pin. Connect FLGND to PGND, and AGND at a single point as close to the AAT1278 as
possible.
C3 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 FL sink current to the maximum (default) movie-mode
current level.
C4 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 AAT1278. Connect OUT to the anode of the Flash LED.
Pin Configuration
CSP-12
(Top View)
CBA
1
2
3
4
C3
C4
C1
C2
B3
B4
A3
A4
B1
B2
A1
A2
PGND
AGND
FLEN
ENSET RSET
IN
SW
SW OUT
FLINH
FLGND
FL
AAT1278
DATA SHEET
1.5A Single Flash LED Driver
3
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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 8.8mW/°C above 25°C ambient.
Absolute Maximum Ratings1
Symbol Description Value Units
IN, OUT, SW Maximum Rating -0.3 to 6.0
V
EN/SET, FLEN,
FLINH, RSET, FL Maximum Rating -0.3 to VIN + 0.3
TJOperating Junction Temperature Range -40 to 150
°C
TSStorage Temperature Range -65 to 150
TLEAD Maximum Soldering Temperature (at Leads, 10 sec) 300
Thermal Information2
Symbol Description Value Units
JA Thermal Resistance 114 °C/W
PDMaximum Power Dissipation3 0.88 W
AAT1278
DATA SHEET
1.5A Single Flash LED Driver
4Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202088A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
Electrical Characteristics
VIN = 3.6V; CIN = COUT = 2.2F; RSET = 107k; L = 1H. TA = -40oC to 85°C unless otherwise noted. Typical values are
at TA = 25°C.
Symbol Description Conditions Min Typ Max Units
Power Supply – Switching Flash Driver
VIN Input Voltage Range 2.7 5.5 V
VOUT(MAX) Maximum Output Voltage 5.5 V
IIN(Q) Supply Current EN/SET = FLEN = IN, Set FL Load = 1.5A 1.4 mA
EN/SET = IN, FLEN = AGND 0.23
IIN(LIM) Input Current Limit VIN - VF = 1V 2 A
ISHDN(MAX) Input Shutdown Current EN/SET, FLEN = AGND 1.0 A
IFL Output Current, Flash Mode RSET = 107k 1.2 1.5 A
IFL(ACC) Flash Current Accuracy RSET = 107k±10 %
IMM(LOAD) Output Current, Movie Mode RSET = 107k, Movie mode current set to
100% 206 mA
fOSC Switching Frequency TA = 25°C 1.5 2.0 2.5 MHz
TSD Over-Temperature Shutdown Threshold 140 °C
TSD(HYS) Over-Temperature Shutdown Hysteresis 15 °C
EN/SET, FLEN
VEN/SET(H),
VFLEN(H)
EN/SET, FLEN Input High Threshold 1.4 V
VEN/SET(L),
VFLEN(L)
EN/SET, FLEN Input Low Threshold 0.4 V
IEN/SET, IFLEN EN/SET, FLEN Input Leakage Current VEN/SET
, VFLEN = IN -1 1μA
VT(FLINH) FLINH Input Threshold Voltage ½ VIN V
RIN(FLINH) FLINH Input Resistance to AGND 200 k
tEN/SET(LO) EN/SET Serial Interface Low Time 0.3 75 s
tEN/SET(HI-MIN) Minimum EN/SET High Time 50 ns
tEN/SET(HI-MAX) Maximum EN/SET High Time 75
s
tEN/SET(OFF) EN/SET Off Timeout Time 500
tEN/SET(LAT) EN/SET Latch Timeout Time 500
tFLEN(ON) FLEN On Delay Time EN/SET = AGND 40
tFLEN(OFF) FLEN Off Delay Time EN/SET = AGND 10
tFLINH(ON) FLINH ON Delay Time 15
AAT1278
DATA SHEET
1.5A Single Flash LED Driver
5
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202088A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
Typical Characteristics
Flash 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
40
50
60
70
80
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
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
Boost Switching Frequency vs. Input Voltage
(Movie Mode; L = 1µH)
Input Voltage (V)
Switching Frequency (MHz)
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
0
0.5
1
1.5
2
2.5
3
85°C
25°C
-40°C
Shutdown Current vs. Input Voltage
(VEN/SET = VFLEN = 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
Supply Current vs. Input Voltage
(VEN = VFLEN = 3.6V)
Input Voltage (V)
Supply Current (µA)
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
0
100
200
300
400
500
600
700
800
900
1000
85°C
25°C
-40°C
Movie Mode LED Current vs. Temperature
(IFL = 206mA/Ch; VIN = 3.6V; L = 1µH)
Temperature (°C)
Output Current (mA)
-40 -15 10 35 60 85
185
190
195
200
205
210
215
220
225
AAT1278
DATA SHEET
1.5A Single Flash LED Driver
6Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202088A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
Typical Characteristics
-4
-3
-2
-1
0
1
2
3
4
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
Movie Mode Current Accuracy vs Input Voltage
(IFL= 206mA; L = 1µH)
Input Voltage (V)
Current Accuracy (%)
Movie Mode Output Ripple
(IFL = 206mA; VIN = 3.6V; L = 1µH)
Time (500ns/div)
VOUT
(AC Coupled)
(50mV/div)
IINDUCTOR
(100mA/div)
VINDUCTOR
(2V/div)
100mA
0V
Flash Mode Output Ripple
(IFL = 1.5A; VIN = 4V; L = 1µH)
Time (200ns/div)
VOUT
(AC Coupled)
(50mV/div)
IINDUCTOR
(50mA/div)
VINDUCTOR
(2V/div)
1.65A
0V
Flash LED Current vs. Temperature
(IFL = 1.5A; VIN = 4.2V; L = 1µH)
Temperature (°C)
Output Current (mA)
-40 -15 10 35 60 85
1420
1440
1460
1480
1500
1520
1540
1560
1580
Flash On Time Delay vs. Input Voltage
(IFL = 1.5A; COUT = 2.2µF; L = 1µH)
Input Voltage (V)
TFLEN_OND (µs)
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
0
10
20
30
40
50
60
70
80
-40°C
25°C
85°C
0
0.5
1
1.5
2
2.5
3
3.5
4
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
-40C
25C
85C
Flash Mode Turn Off Time vs Input Voltage
(IFL = 1.5A; COUT= 2.2µF; L = 1µH)
Input Voltage (V)
TFLEN_OFFD (µs)
AAT1278
DATA SHEET
1.5A Single Flash LED Driver
7
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202088A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
Typical Characteristics
Movie Mode Line Transient
(IFL = 206mA; VIN = 4.2V to 3.6V)
Time (50µs/div)
IFL
(AC Coupled)
(50mA/div)
VIN
(500mV/div)
4.2V
3.6V
Flash Turn On Characteristic
(IFL = 1.5A; VIN = 3.6V; COUT = 2.2µF; L = 1µH)
Time (50µs/div)
VFLEN
(2V/div)
IFL
(1A/div)
VFL
(2V/div)
VOUT
(2V/div)
0A
0V
0V
0V
Flash Turn Off Characteristic
(IFL = 1.5A; VIN = 3.6V; COUT = 2.2µF; L = 1µH)
Time (1µs/div)
VFLEN
(2V/div)
IFL
(1A/div)
VFL
(2V/div)
VOUT
(2V/div)
0A
0V
2V
0V
Movie Mode to Flash Turn On Characteristic
(IFL = 206mA to 1.5A; VIN = 3.6V; L = 1µH)
Time (50µs/div)
VFLEN
(2V/div)
IFLOUTX
(1A/div)
VFL
(500mV/div)
VOUT
(2V/div)
0A
0V
2V
0V
Movie Mode Turn On Characteristic
(IFL = 206mA; VIN = 3.6V; L = 1µH)
Time (100µs/div)
VEN/SET
(5V/div)
IFL
(200mA/div)
VFL
(500mV/div)
VOUT
(2V/div)
0V
0A
0V
0V
Movie Mode Transition Characteristic
(IFL = 206mA to 376mA; COUT = 0.22µF;
VIN = 3.6V; L = 1µH)
Time (100µs/div)
VEN/SET
(2V/div)
IFL
(200mA/div)
VFL
(500mV/div)
VOUT
(2V/div)
0V
0A
0V
0V
AAT1278
DATA SHEET
1.5A Single Flash LED Driver
8Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202088A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
Typical Characteristics
EN, FLEN High Threshold Voltage
vs. Input Voltage
Input Voltage (V)
VEN/SET(H), VFLEN(H) (V)
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
85°C
25°C
-40°C
EN, FLEN Low Threshold Voltage
vs. Input Voltage
Input Voltage (V)
VEN/SET(L), VFLEN(L) (V)
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
85°C
25°C
-40°C
EN/SET Off Timeout vs. Input Voltage
Input Voltage (V)
TEN/SET(OFF) (µs)
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
50
100
150
200
250
300
85°C
25°C
-40°C
EN/SET Latch Timeout vs. Input Voltage
Input Voltage (V)
TEN/SET(LAT) (µs)
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
50
100
150
200
250
300
85°C
25°C
-40°C
AAT1278
DATA SHEET
1.5A Single Flash LED Driver
9
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202088A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
Functional Description
The AAT1278 is a boost converter with a current regu-
lated output designed to drive high current white LED
used in camera flash applications. The AAT1278 has a
constant current sink channel to accurately regulate the
current flow through a high current, high intensity white
flash LED. The AAT1278 has two basic operating modes;
a flash mode controlled by the FLEN pin and the movie/
torch light mode controlled through the AS2Cwire inter-
face.
Flash Mode
A flash pulse may be initiated by pulling the FLEN input
pin from a logic low-to-high state, which initiates a flash
pulse. The maximum flash current in the AAT1278 is set
by an external resistor, RSET, which sets the flash current
and the maximum movie-mode current.
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 AAT1278
to revert the flash LED current to its maximum level,
assuming that the FLEN pin is still active (high).
Movie (Torch) Mode
The movie / torch mode current level, and the flash to
maximum movie mode current ratio are programmed by
the AAT1278 AS2Cwire interface. The movie-mode cur-
rent level can be adjusted to one of 16 steps using a
logarithmic scale where each code level is 1dB below the
previous code. The flash to maximum movie mode cur-
rent ratio can be set from 2:1 to OFF with respect to the
maximum programmed flash current as set by the RSET
resistor. The manual FLEN signal has priority over mov-
ie-mode operation.
Functional Block Diagram
System Control Enable
and AS2C Interface
OUT (to Flash LED)
FL
FLGND
RSET
PGND
AGND
FLEN
EN/SET
IN
SW
FLINH
AAT1278
DATA SHEET
1.5A Single Flash LED Driver
10 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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Movie mode operation is controlled entirely by the
AS2Cwire interface via the EN/SET pin. The FLEN signal
will override movie-mode AAT1278 operation when tog-
gled to a logic high level. The part will not reenter movie
mode when FLEN is brought low. To reenter movie mode
after a flash event the part must be cycled off and back
on to reset the movie mode and reprogrammed via the
AS2Cwire interface to the desired movie mode operation.
Shutdown and Output Disconnect (True
Load Disconnect)
A typical synchronous step-up (boost) converter has a
conduction path from the input to the output via the
body diode of the P-channel MOSFET. The AAT1278
design disconnects this body diode from the output and
eliminates this conduction path. This enables the
AAT1278 to provide true load disconnect during shut-
down and inrush current limit at turn-on.
Over-Voltage Protection
(Open Flash LED, Open Circuit)
The AAT1278 boost converter output is voltage limited by
internal overvoltage protection circuitry to prevent dam-
age to the device in the event an open LED or open circuit
condition occurs. During an open circuit condition, the
output voltage will rise to 5.5V (typical). The OVP circuit
disables the boost converter to prevent the output voltage
from rising above 5.5V. Once the open circuit condition is
removed, normal boost operation will resume.
Short Circuit Protection
The AAT1278 is equipped with an auto-disable feature
for the flash LED channel. After the IC is enabled and
system start up commences, a test current of 2-3mA
(typical) is forced through the sink channel. The channel
will be disabled if the voltage of the SINK pin does not
drop to a predetermined threshold. This feature is very
convenient for disabling the current sink in the event the
flash LED fails to a short circuit. This small test current
is added to the set output current in both Flash and
movie mode conditions.
Over-Temperature Protection
The AAT1278 has internal thermal protection circuitry to
disable the device if the internal power dissipation exceeds
a preset thermal limit. The junction over-temperature
threshold is 140°C with 15°C of temperature hysteresis.
During flash or movie-mode operation, if an environmen-
tal condition, flash current sink, or the boost converter
causes the internal die temperature to rise above 140°C,
the boost converter will be shut down. The boost con-
verter output operation will automatically recover when
the over-temperature fault condition is removed.
Application Information
Flash Mode LED Current
Flash sink current can be programmed up to a maximum
of 1.5A. The maximum flash current is set by the RSET
resistor. For the desired flash current, the resistor value
can be calculated using the following equation:
1A
I
FL(MAX)
R
SET
= ∙ 162kΩ
A flash event is initiated by asserting the FLEN pin. A
flash event is automatically terminated when FLEN is
deasserted. Any time that the FLINH pin is asserted, the
default movie-mode current level will appear at FL chan-
nel. The default movie mode current level will be main-
tained on FL as long as the FLINH and FLEN pins are
asserted. In addition to setting the flash current via RSET,
the flash current can be changed after FLEN is asserted
by programming the movie mode current register with
16 different steps.
AS2Cwire Control
of Movie Mode Operation
In the AAT1278 control of the movie mode operation is
managed by the Advanced Simple Serial Control
(AS2Cwire) interface. AS2Cwire relies on the number of
rising edges of the EN/SET pin to address and load inter-
nal data registers. Referring to Table 1:
Address 0 controls the movie mode (MM) current level
as a percentage of the maximum movie mode current
level.
Address 3 sets the maximum possible current for movie
mode operation. The maximum movie mode current is
set as a fraction of the flash current with a peak value
of 1/2 and default value of 1/7.3.
The last column in Table 1 shows the default values for
each of the address registers.
AAT1278
DATA SHEET
1.5A Single Flash LED Driver
11
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202088A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012
Address
EN/SET
Rising
Edges Function
Default
(No Programming)
017
Movie Mode
Current 100%
1 Not Used
2 Not Used
320
Flash/Movie
Mode Cur-
rent Ratio
7.3:1
Table 1: AS2Cwire Serial Interface Addressing.
AS2Cwire Serial Interface
AS2Cwire latches data or address after the EN/SET pin
has been held high for longer than tLAT (500s). Address
or data are differentiated by the number of EN/SET rising
edges. Since the data registers are 4 bits each, the dif-
ferentiating number of pulses is 24 or 16, so that Address
0 is signified by 17 rising edges, and Address 3 by 20
rising edges. Data is inclusively applied to any number of
rising edges between 1 and 16. A typical write protocol
is a burst of EN/SET rising edges which signify a particu-
lar address that is followed by a pause with EN/SET held
high for the prescribed tLAT timeout period, then a burst
of rising edges signifying data, and a tLAT timeout for the
data registers. Once an address is set, then multiple
writes to the corresponding data register are allowed.
Address 0 is the default address on the first rising edge
after the AAT1278 has been disabled. When EN/SET is
transitioned from high to low and held low longer than
tOFF (500s), the device enters a shutdown mode and
draws less than 1uA from the input supply. All data and
address are cleared (reset to 0) during shutdown.
AS2Cwire addressing allows for control of the movie
mode output current, and the ratio of movie-mode cur-
rent to flash current. If there are no programmed write
instructions applied to the EN/SET pin prior to the asser-
tion of the FLEN pin and the device is enabled, then all
registers will be loaded with their default values shown in
Table 1. In the event that the number of rising edges
applied at the EN/SET pin is less than 17, the internal
state machine will interpret instruction to program the
output currents to the desired current level for movie-
mode operation.
Movie Mode Current – Address 0
The AAT1278 movie mode current settings are con-
trolled using the AS2Cwire interface. The default ratio
between the flash current level and maximum movie
mode current level is 7.3:1.
For example, if an RSET value of 107k is chosen, then
the flash current is set to 1500mA. For movie mode
operation, the maximum current available is then:
I
FL(MAX)
7.3
1500mA
7.3
I
MOVIE MODE
= = = 206m
A
Address Data
1
EN/SET
216 17
Address
Data Reg 1
12 . . . n ≤ 16
01
0n
THI
TLO TLAT TLAT
Figure 1: AS2Cwire Serial Interface Timing Diagram.
AAT1278
DATA SHEET
1.5A Single Flash LED Driver
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* Denotes the default value.
Address 0 controls precise movie mode current levels.
The movie mode current can be adjusted in a logarithmic
fashion to one of 16 steps represented as a fraction of
the maximum movie mode current in Table 2. On initial
EN, the movie-mode output immediately supplies 100%
of the set movie-mode current.
Data Percentage of Maximum MM Current
1* 100%
2 89%
3 79%
4 71%
5 63%
6 56%
7 50%
8 45%
9 40%
10 36%
11 32%
12 28%
13 25%
14 22%
15 20%
16 0%
Table 2: Address 0, Movie Mode (MM)
Current Programming.
Flash to Maximum Movie Mode
Current Ratio – Address 3
The maximum movie mode current is a fixed ratio of the
flash current controlled by Address 3. The ratio may be
varied from 2:1 to OFF in 16 linear steps as shown in
Table 3. The default value for Address 3 is Data = 4 and
represents a flash to maximum movie mode current level
of 7.3 to 1. The default maximum movie mode current
can be calculated:
I
FL(MAX)
7.3
I
MOVIE MODE
=
For example, if an RSET value of 107k is chosen, then
the flash current is set to 1500mA. For movie mode
operation, the maximum current available is then:
1500mA
7.3
I
MOVIE MODE
= = 206m
A
The maximum movie mode current level can be calcu-
lated using the following equation:
162kΩ ∙ A
R
SET
1
FL to MM Ratio
I
MOVIE MODE
= ∙ = Max Movie Mode Current
Data Flash to Movie Mode Ratio
1 2:1
2 3.8:1
3 5.5:1
4* 7.3:1
5 8.9:1
6 10.5:1
7 12.2:1
8 13.8:1
9 14.9:1
10 16.5:1
11 18:1
12 19.6:1
13 21.1:1
14 22.6:1
15 24:1
16 OFF
Table 3: Address 3, Flash/
Movie Mode Current Ratio.
Shutdown
Since the flash current sink is the only power returns for
the flash LED loads, there is no leakage current to load
if all the sink switches are disabled. When the EN/SET
pin is held low for an amount of time greater than tOFF
(500s), the AAT1278 flash boost converter section
enters shutdown mode and draws less than 1A from the
input power source. All data and address registers for
the flash and/or movie mode are cleared (reset to 0)
during shutdown.
Selecting the Boost Inductor
The AAT1278 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.
AAT1278
DATA SHEET
1.5A Single Flash LED Driver
13
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Selecting the Boost Capacitors
In general, it is a good design practice to place a decou-
pling capacitor (input capacitor) between the IN and
ground. An input capacitor in the range of 2.2F to 10F
is recommended. A larger input capacitor in this applica-
tion may be required for stability, transient response,
and/or ripple performance. The high output ripple inher-
ent 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 AAT1278 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) dur-
ing the power switch ON interval. A 2.2F ceramic output
capacitor is recommended (see Table 4). Typically, 6.3V
or 10V rated capacitors are required for this flash LED
boost output application. Ceramic capacitors selected as
small as 0603 are available which meet these require-
ments. MLC capacitors exhibit significant capacitance
reduction with applied voltage. Output ripple measure-
ments should confirm that output voltage droop and
operating stability are within acceptable limits. Voltage
de-rating can minimize this factor, but results may vary
with package size among specific manufacturers. To
maintain stable operation at full load, the output capaci-
tor should be selected to maintain VOUT between 100mV
and 200mV. The boost converter input current flows dur-
ing 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 AAT1278 1.5A
step-up regulator is shown in Figures 3 and 4. 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
LED to maximize heatsinking capability. This may be
necessary when using high current application and
long flash duration application.
Manufacturer Part Number
Inductance
(H)
Saturated Rated
Current (A)
DCR
(m)
Size (mm)
LxWxH Type
Cooper Bussmann SD3812-1R0-R 1 2.69 48 4.0 x 4.0 x 1.2 shielded drum core
Cooper Bussmann SDH3812-1R0-R 1 3 45 3.8 x 3.8 x 1.2 shielded drum core
Cooper Bussmann SD10-1R0-R 1 2.25 44.8 5.2 x 5.2 x 1.0 shielded drum core
Sumida CDH38D11/S 1 2.69 48 4.0 x 4.0 x 1.2 shielded drum core
Coilcraft LPS4012-102NLC 1 2.5 60 4.1 x 4.1 x 1.2 shielded drum core
Table 4: 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
Murata GRM188R71A225KE15 2.2 10 X7R 0603
Murata GRM21BR70J225KA01 2.2 6.3 X7R 0805
Murata GRM21BR71A225KA01 2.2 10 X7R 0805
Murata GRM219R61A475KE19 4.7 10 X5R 0805
Murata GRM21BR71A106KE51 10 10 X7R 0805
Table 5: Typical Suggested Surface Mount Capacitors.
AAT1278
DATA SHEET
1.5A Single Flash LED Driver
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2.2μF
C2
2.2μF
C1
R1
133k
D1
VIN
V
OUT
VDD
1
GP5
2
GP4
3
GP3
4GP2 5
GP1 6
GP0 7
VSS 8
U2
PIC12F675
1μF
C3
100k
R4
(opt)
330
R8
LED1
RED
1
23
45
0SW4
FLINH
1
23
45
0
SW1
Movie Mode Control
10K
R5
LED2
GRN
330
R9
GND
100K
R2
JP2
10k
R3
JP3
EN/SET
JP1
MCU
1
23
45
0SW2
Flash/Movie Mode Current Ratio
10K
R6
10K
R7
1μH
L1
AGND
A3
IN
B2
OUT C4
EN/SET
A1
FL
C1
PGND
A4
FLEN
A2
SW B4
SW B3
FLINHIBIT C3
FLGND C2
RSET B1
U1
AAT1278 CSP-12
NA
C4
1
23
45
0SW3
FLEN
100k
R10
Figure 2: AAT1278 Evaluation Board Schematic.
Figure 3: AAT1278 Evaluation Board Figure 4: AAT1278 Evaluation Board
Top Side Layout. Bottom Side Layout.
AAT1278
DATA SHEET
1.5A Single Flash LED Driver
15
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Component Part Number Description Manufacturer
U1 AAT1278IUP 1.5A Step-Up Current Regulator for Flash LED;CSP-12
Package Skyworks
U2 PIC12F675 8-bit CMOS,FLASH-based uC; 8-pin SOIC package Microchip
SW1-SW4 PTS645TL50 Switch Tact, SPST, 5mm ITT Industries
R1 Chip Resistor 133k,1%,1/16W; 0402 Vishay
R2,R4,R10 Chip Resistor 100k, 1%, 1/10W; 0603 Vishay
R3,R5,R6,R7 Chip Resistor 10k, 1%, 1/10W; 0603 Vishay
R8.R9 Chip Resistor 330, 1%, 1/10W; 0603 Vishay
JP1, JP2, JP3 PRPN401PAEN Conn. Header, 2mm zip Sullins Electronics
C1,C2 GRM188R71A225KE15 2.2uF, 10V, X7R, 0603 MuRata
C3 GRM216R61A105KA01 1uF, 10V, X5R, 0805 MuRata
L1 SD3812-1R0-R Drum Core, 1uH, 2.69A, 48mCooper Bussmann
D1 FCW401Z White Flash LED Seoul Semiconductor
LED1 0805KRCT Red LED; 0805 HB
LED2 0805KGCT Green LED; 0805 HB
Table 6: AAT1278 Evaluation Board Bill of Materials.
AAT1278
DATA SHEET
1.5A Single Flash LED Driver
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1. YW = Year and Week code.
2. Sample stock is generally held on part numbers listed in BOLD.
Ordering Information
Package Marking1Part Number(Tape and Reel)2
CSP-12 U3YW AAT1278IUP-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-12
Symbol Min Nominal Max
A 0.610 0.695 0.780
A1 0.220 0.245 0.270
A2 0.355 0.380 0.405
A3 0.035 0.070 0.105
D 2.035 2.070 2.105
E 1.495 1.530 1.565
D1 1.500 BSC
E1 1.000 BSC
SD 0.250 BSC
SE N/A
e 0.500 BSC
b 0.285 0.310 0.335
X 0.300 - -
Y 0.300 - -
X1 - 0.100 -
Y1 - 0.200 -
N 12 Balls
All dimensions in millimeters.
CB
E
A
Y
U3
W
Y1
LINE_1
LINE_2
1/2 D
1/2 E
ENSET
PIN A1 Indication
Y
X
X1
D
A1 A2 A3
1
2
3
4
E1
e
D1
SD
(Bottom View) (Side View)
(Side View)
(Top View)
A
+ + +
+ + +
+ + +
+ + +
NxØb
Ø 0.2 (Ref.)
AAT1278
DATA SHEET
1.5A Single Flash LED Driver
17
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Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved.
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