Data Sheets - Skyworks Solutions, Inc.

DATA SHEET
AAT1278
1.5A Single Flash LED Driver
General Description
Features
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, pulsewidth 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 ideally suited in all single cell, Li-ion-powered applications.
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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 initiate the flash operation and a Flash Inhibit pin which
reduces the flash current to movie-mode levels during
high battery demand.
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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
•
•
•
•
•
The maximum flash and movie-mode current is set by
one external resistor where the ratio of flash to moviemode current is set at approximately 7.3:1. The AAT1278
can drive one high current LED.
LED Photo Flash / Torch
Camera Enabled Mobile Devices
Cellphones/Smartphones
Digital Still Cameras (DSCs)
Multimedia Mobile Phones
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 1.0μA.
The AAT1278 is available in a Pb-free, thermally-enhanced
CSP-12 package and operates over the -40°C to 85°C
temperature range.
Typical Application
L1 1μH
VBAT = 2.7V to 5.5V
SW
IN
OUT
CIN
2.2μF
COUT
2.2μF
Flash LED
AAT1278
Enable/Set Input
EN/SET
Flash Enable
FLEN
Flash Inhibit
FLINH
FL
RSET
RSET
PGND AGND FLGND
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
1
DATA SHEET
AAT1278
1.5A Single Flash LED Driver
Pin Descriptions
Pin #
Symbol
Description
A1
EN/SET
A2
FLEN
Flash enable pin. A low-to-high transition on the FLEN pin initiates a flash pulse and a high-to-low
transition on the FLEN pin terminates a flash 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 flash current for the
current sink FL.
B2
IN
B3, B4
C1
SW
FL
C2
FLGND
C3
FLINH
C4
OUT
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.
Flash output boost converter power input. Connect IN to the input power source. Connect a 2.2μF or larger
ceramic capacitor from IN to PGND and locate as close as possible to the AAT1278 package for optimum
performance.
Boost converter switching node. Connect a 1μH inductor between SW and IN.
LED Flash current sink pin. Connect the cathode of Flash LED to FL.
Flash ground pin. Connect FLGND to PGND, and AGND at a single point as close to the AAT1278 as
possible.
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.
Power output of the boost converter. Connect a 2.2μF 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)
4
3
2
1
2
PGND
SW
OUT
A4
B4
C4
AGND
SW
FLINH
A3
B3
C3
FLEN
IN
FLGND
A2
B2
C2
ENSET
RSET
FL
A1
B1
C1
A
B
C
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
DATA SHEET
AAT1278
1.5A Single Flash LED Driver
Absolute Maximum Ratings1
Symbol
IN, OUT, SW
EN/SET, FLEN,
FLINH, RSET, FL
TJ
TS
TLEAD
Description
Value
Maximum Rating
-0.3 to 6.0
Maximum Rating
-0.3 to VIN + 0.3
Operating Junction Temperature Range
Storage Temperature Range
Maximum Soldering Temperature (at Leads, 10 sec)
Units
V
-40 to 150
-65 to 150
300
°C
Value
Units
114
0.88
°C/W
W
Thermal Information2
Symbol
JA
PD
Description
Thermal Resistance
Maximum Power Dissipation3
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.
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
3
DATA SHEET
AAT1278
1.5A Single Flash LED Driver
Electrical Characteristics
VIN = 3.6V; CIN = COUT = 2.2μF; RSET = 107kΩ; L = 1μH. TA = -40oC to 85°C unless otherwise noted. Typical values are
at TA = 25°C.
Symbol
Description
Conditions
Power Supply – Switching Flash Driver
Input Voltage Range
VIN
VOUT(MAX)
Maximum Output Voltage
IIN(Q)
Supply Current
IIN(LIM)
ISHDN(MAX)
IFL
IFL(ACC)
Input Current Limit
Input Shutdown Current
Output Current, Flash Mode
Flash Current Accuracy
IMM(LOAD)
Output Current, Movie Mode
fOSC
TSD
Switching Frequency
Over-Temperature Shutdown Threshold
TSD(HYS)
Over-Temperature Shutdown Hysteresis
EN/SET, FLEN
VEN/SET(H),
EN/SET, FLEN Input High Threshold
VFLEN(H)
VEN/SET(L),
EN/SET, FLEN Input Low Threshold
VFLEN(L)
IEN/SET, IFLEN EN/SET, FLEN Input Leakage Current
VT(FLINH)
FLINH Input Threshold Voltage
RIN(FLINH)
FLINH Input Resistance to AGND
tEN/SET(LO)
EN/SET Serial Interface Low Time
tEN/SET(HI-MIN) Minimum EN/SET High Time
tEN/SET(HI-MAX) Maximum EN/SET High Time
tEN/SET(OFF)
EN/SET Off Timeout Time
tEN/SET(LAT)
EN/SET Latch Timeout Time
tFLEN(ON)
FLEN On Delay Time
tFLEN(OFF)
FLEN Off Delay Time
FLINH ON Delay Time
tFLINH(ON)
4
Min
Typ
Max
Units
5.5
5.5
V
V
mA
2.7
EN/SET = FLEN = IN, Set FL Load = 1.5A
EN/SET = IN, FLEN = AGND
VIN - VF = 1V
EN/SET, FLEN = AGND
RSET = 107kΩ
RSET = 107kΩ
RSET = 107kΩ, Movie mode current set to
100%
TA = 25°C
1.4
0.23
2
1.5
±10
A
μA
A
%
206
mA
1.0
1.2
1.5
2.0
140
15
2.5
1.4
VEN/SET, VFLEN = IN
V
-1
0.4
V
1
μA
V
kΩ
μs
ns
½ VIN
200
0.3
75
50
75
500
500
EN/SET = AGND
EN/SET = AGND
MHz
°C
°C
40
10
15
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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μs
DATA SHEET
AAT1278
1.5A Single Flash LED Driver
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
204mA
104mA
52mA
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
4.7
5.1
5.5
Input Voltage (V)
Boost Switching Frequency vs. Input Voltage
Shutdown Current vs. Input Voltage
(VEN/SET = VFLEN = 0V)
3
0.03
Shutdown Current (µA)
Switching Frequency (MHz)
4.3
Input Voltage (V)
(Movie Mode; L = 1µH)
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)
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Supply Current vs. Input Voltage
Movie Mode LED Current vs. Temperature
(VEN = VFLEN = 3.6V)
(IFL = 206mA/Ch; VIN = 3.6V; L = 1µH)
225
1000
Output Current (mA)
900
Supply Current (µA)
3.9
800
700
600
500
400
300
85°C
25°C
-40°C
200
100
0
2.7
3.1
3.5
3.9
4.3
Input Voltage (V)
4.7
5.1
5.5
220
215
210
205
200
195
190
185
-40
-15
10
35
60
85
Temperature (°C)
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
5
DATA SHEET
AAT1278
1.5A Single Flash LED Driver
Typical Characteristics
Movie Mode Current Accuracy vs Input Voltage
Movie Mode Output Ripple
(IFL= 206mA; L = 1µH)
(IFL = 206mA; VIN = 3.6V; L = 1µH)
Current Accuracy (%)
4
3
VOUT
(AC Coupled)
(50mV/div)
2
1
0
VINDUCTOR
(2V/div)
-1
0V
-2
IINDUCTOR
(100mA/div)
-3
-4
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 vs. Temperature
(IFL = 1.5A; VIN = 4V; L = 1µH)
(IFL = 1.5A; VIN = 4.2V; L = 1µH)
1580
VINDUCTOR
(2V/div)
Output Current (mA)
VOUT
(AC Coupled)
(50mV/div)
0V
IINDUCTOR
(50mA/div)
1560
1540
1520
1500
1480
1460
1440
1420
1.65A
-40
-15
4
70
3.5
60
3
50
40
30
20
-40°C
25°C
85°C
10
0
4.3
Input Voltage (V)
6
TFLEN_OFFD (µs)
TFLEN_OND (µs)
80
3.9
4.7
85
(IFL = 1.5A; COUT= 2.2µF; L = 1µH)
(IFL = 1.5A; COUT = 2.2µF; L = 1µH)
3.5
60
Flash Mode Turn Off Time vs Input Voltage
Flash On Time Delay vs. Input Voltage
3.1
35
Temperature (°C)
Time (200ns/div)
2.7
10
5.1
2.5
2
1.5
1
-40C
25C
85C
0.5
5.5
0
2.7
3.1
3.5
3.9
4.3
4.7
Input Voltage (V)
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
5.1
5.5
DATA SHEET
AAT1278
1.5A Single Flash LED Driver
Typical Characteristics
Movie Mode Line Transient
Flash Turn On Characteristic
(IFL = 206mA; VIN = 4.2V to 3.6V)
(IFL = 1.5A; VIN = 3.6V; COUT = 2.2µF; L = 1µH)
4.2V
VIN
(500mV/div)
3.6V
IFL
(AC Coupled)
(50mA/div)
VFLEN
(2V/div)
VOUT
(2V/div)
0V
0V
VFL
(2V/div)
0V
IFL
(1A/div)
0A
Time (50µs/div)
Time (50µs/div)
VFLEN
(2V/div)
VOUT
(2V/div)
Flash Turn Off Characteristic
Movie Mode to Flash Turn On Characteristic
(IFL = 1.5A; VIN = 3.6V; COUT = 2.2µF; L = 1µH)
(IFL = 206mA to 1.5A; VIN = 3.6V; L = 1µH)
VFLEN
(2V/div)
VOUT
(2V/div)
0V
2V
VFL
(2V/div)
0V
VFL
(500mV/div)
IFL
(1A/div)
0A
IFLOUTX
(1A/div)
0V
2V
0V
0A
Time (1µs/div)
VEN/SET
(5V/div)
VOUT
(2V/div)
Time (50µs/div)
Movie Mode Turn On Characteristic
Movie Mode Transition Characteristic
(IFL = 206mA; VIN = 3.6V; L = 1µH)
(IFL = 206mA to 376mA; COUT = 0.22µF;
VIN = 3.6V; L = 1µH)
0V
VEN/SET
(2V/div)
VOUT
(2V/div)
0V
0V
VFL
(500mV/div)
IFL
(200mA/div)
0V
VFL
(500mV/div)
0V
IFL
(200mA/div)
0V
0A
0A
Time (100µs/div)
Time (100µs/div)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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7
DATA SHEET
AAT1278
1.5A Single Flash LED Driver
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
0.9
0.8
0.7
0.6
0.4
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
2.7
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
EN/SET Off Timeout vs. Input Voltage
EN/SET Latch Timeout vs. Input Voltage
300
300
250
250
200
150
85°C
25°C
-40°C
100
50
2.7
3.1
Input Voltage (V)
TEN/SET(LAT) (µs)
TEN/SET(OFF) (µs)
1.1
1.0
0.5
0.4
3.1
3.5
3.9
4.3
Input Voltage (V)
8
85°C
25°C
-40°C
1.2
4.7
5.1
85°C
25°C
-40°C
200
150
100
5.5
50
2.7
3.1
3.5
3.9
4.3
4.7
Input Voltage (V)
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
5.1
5.5
DATA SHEET
AAT1278
1.5A Single Flash LED Driver
Functional Block Diagram
SW
OUT (to Flash LED)
FL
IN
EN/SET
System Control Enable
and AS2C Interface
FLEN
FLGND
RSET
FLINH
AGND
PGND
Functional Description
The AAT1278 is a boost converter with a current regulated 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 interface.
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 communication, 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 current 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 current 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 movie-mode operation.
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
9
DATA SHEET
AAT1278
1.5A Single Flash LED Driver
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 toggled 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 shutdown 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 damage 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-
10
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 converter 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:
RSET =
1A
∙ 162kΩ
IFL(MAX)
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 channel. The default movie mode current level will be maintained 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 internal 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.
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
DATA SHEET
AAT1278
1.5A Single Flash LED Driver
Address
EN/SET
Rising
Edges
0
17
1
2
3
20
Function
Default
(No Programming)
Movie Mode
Current
Not Used
Not Used
Flash/Movie
Mode Current Ratio
100%
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 (500μs). Address
or data are differentiated by the number of EN/SET rising
edges. Since the data registers are 4 bits each, the differentiating 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 particular 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 (500μs), 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 current to flash current. If there are no programmed write
instructions applied to the EN/SET pin prior to the assertion 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 moviemode operation.
Movie Mode Current – Address 0
The AAT1278 movie mode current settings are controlled 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 107kΩ is chosen, then
the flash current is set to 1500mA. For movie mode
operation, the maximum current available is then:
IFL(MAX)
1500mA
=
= 206mA
IMOVIE MODE = 7.3
7.3
Address
Data
T HI
T LO
TLAT
TLAT
EN/SET
1
Address
Data Reg 1
2
16
17
1
0
2...
n ≤ 16
1
0
n
Figure 1: AS2Cwire Serial Interface Timing Diagram.
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DATA SHEET
AAT1278
1.5A Single Flash LED Driver
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*
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
100%
89%
79%
71%
63%
56%
50%
45%
40%
36%
32%
28%
25%
22%
20%
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:
IFL(MAX)
IMOVIE MODE = 7.3
For example, if an RSET value of 107kΩ is chosen, then
the flash current is set to 1500mA. For movie mode
operation, the maximum current available is then:
IMOVIE MODE =
1500mA
= 206mA
7.3
The maximum movie mode current level can be calculated using the following equation:
IMOVIE MODE =
162kΩ ∙ A
1
∙
= Max Movie Mode Current
RSET
FL to MM Ratio
Data
Flash to Movie Mode Ratio
1
2
3
4*
5
6
7
8
9
10
11
12
13
14
15
16
2:1
3.8:1
5.5:1
7.3:1
8.9:1
10.5:1
12.2:1
13.8:1
14.9:1
16.5:1
18:1
19.6:1
21.1:1
22.6:1
24:1
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
(500μs), the AAT1278 flash boost converter section
enters shutdown mode and draws less than 1μA 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 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.
* Denotes the default value.
12
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DATA SHEET
AAT1278
1.5A Single Flash LED Driver
Selecting the Boost Capacitors
In general, it is a good design practice to place a decoupling capacitor (input capacitor) between the IN and
ground. 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 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) during the power switch ON interval. A 2.2μF 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 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
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 capacitor 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 parasitic 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 following PCB layout guidelines should be considered:
1. 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.
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
(μH)
Saturated Rated
Current (A)
DCR
(mΩ)
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
2.69
2.5
48
45
44.8
48
60
Size (mm)
LxWxH
4.0
3.8
5.2
4.0
4.1
x
x
x
x
x
4.0
3.8
5.2
4.0
4.1
x
x
x
x
x
1.2
1.2
1.0
1.2
1.2
Type
shielded
shielded
shielded
shielded
shielded
drum
drum
drum
drum
drum
core
core
core
core
core
Table 4: Typical Suggested Surface Mount Inductors.
Manufacturer
Part Number
Capacitance (μF)
Voltage Rating (V)
Temp Co.
Case Size
Murata
Murata
Murata
Murata
Murata
Murata
GRM185R60J225KE26
GRM188R71A225KE15
GRM21BR70J225KA01
GRM21BR71A225KA01
GRM219R61A475KE19
GRM21BR71A106KE51
2.2
2.2
2.2
2.2
4.7
10
6.3
10
6.3
10
10
10
X5R
X7R
X7R
X7R
X5R
X7R
0603
0603
0805
0805
0805
0805
Table 5: Typical Suggested Surface Mount Capacitors.
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13
DATA SHEET
AAT1278
1.5A Single Flash LED Driver
GND
VIN
R3
JP1
MCU
R5
10K
2
4
Movie Mode Control
Flash/Movie Mode Current Ratio
0
FLEN
0
R6
10K
R7
10K
U2
1
2
3
4
SW1
0
1
3
5
SW2
2
4
VDD
GP5
GP4
GP3
VSS
GP0
GP1
GP2
PIC12F675
1
3
5
8
7
6
5
FLINH
2
4
1
3
5
SW4
JP2
C3
1μF
R10
100k
R8
330
R9
330
R4
100k
(opt)
VOUT
LED1
RED
LED2
GRN
SW3
2
4
0
10k
D1
1
3
5
U1
JP3
EN/SET
A3
A1
C1
A2
R2
100K
B2
A4
C4
NA
C1
2.2μF
AGND
EN/SET
FL
FLEN
IN
PGND
RSET
FLGND
B1
C2
FLINHIBIT
SW
SW
OUT
C3
B3
B4
C4
L1
1μH
AAT1278 CSP-12
R1
133k
Figure 2: AAT1278 Evaluation Board Schematic.
Figure 3: AAT1278 Evaluation Board
Top Side Layout.
14
Figure 4: AAT1278 Evaluation Board
Bottom Side Layout.
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C2
2.2μF
DATA SHEET
AAT1278
1.5A Single Flash LED Driver
Component
Part Number
U1
AAT1278IUP
U2
SW1-SW4
R1
R2,R4,R10
R3,R5,R6,R7
R8.R9
JP1, JP2, JP3
C1,C2
C3
L1
D1
LED1
LED2
PIC12F675
PTS645TL50
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
PRPN401PAEN
GRM188R71A225KE15
GRM216R61A105KA01
SD3812-1R0-R
FCW401Z
0805KRCT
0805KGCT
Description
1.5A Step-Up Current Regulator for Flash LED;CSP-12
Package
8-bit CMOS,FLASH-based uC; 8-pin SOIC package
Switch Tact, SPST, 5mm
133kΩ,1%,1/16W; 0402
100kΩ, 1%, 1/10W; 0603
10kΩ, 1%, 1/10W; 0603
330Ω, 1%, 1/10W; 0603
Conn. Header, 2mm zip
2.2uF, 10V, X7R, 0603
1uF, 10V, X5R, 0805
Drum Core, 1uH, 2.69A, 48mΩ
White Flash LED
Red LED; 0805
Green LED; 0805
Manufacturer
Skyworks
Microchip
ITT Industries
Vishay
Vishay
Vishay
Vishay
Sullins Electronics
MuRata
MuRata
Cooper Bussmann
Seoul Semiconductor
HB
HB
Table 6: AAT1278 Evaluation Board Bill of Materials.
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15
DATA SHEET
AAT1278
1.5A Single Flash LED Driver
Ordering Information
Package
Marking1
Part 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
E1
0.610
0.220
0.355
0.035
2.035
1.495
0.695
0.245
0.380
0.070
2.070
1.530
1.500 BSC
1.000 BSC
0.250 BSC
N/A
0.780
0.270
0.405
0.105
2.105
1.565
b
X
Y
X1
Y1
N
0.500 BSC
0.285
0.300
0.300
-
0.310
0.100
0.200
12 Balls
+
+
+
4
+
+
+
3
+
+
+
2
+
+
+
1
C
B
E
A
A
(Bottom View)
0.335
-
A3
(Side View)
Y1
NxØb
U 3
LINE_1
Y W
LINE_2
X1
e
A2
A1
All dimensions in millimeters.
Y
(Side View)
1/2 D
A
A1
A2
A3
D
E
D1
E1
SD
SE
e
D
Max
X
Nominal
D1
Min
SD
Symbol
ENSET
1/2 E
Ø 0.2 (Ref.)
PIN A1 Indication
(Top View)
1. YW = Year and Week code.
2. Sample stock is generally held on part numbers listed in BOLD.
16
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DATA SHEET
AAT1278
1.5A Single Flash LED Driver
Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved.
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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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