DATA SHEET
AAT1277
1.5A Step-Up Current Regulator for Flash LEDs
General Description
Features
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.
• VIN Range: 2.7V to 5.5V
• Dual Channel Output
• Up to 1.5A Regulated Output Current (750mA per
channel)
• Up to 85% Efficiency with Small Inductor (1μH)
• 2 MHz Switching Frequency
• Separate Flash/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 < 1.0μA
• 18 Ball 1.5mm x 2.4mm CSP Package
• -40°C to +85°C Operating Temperature Range
The AAT1277 maintains output current regulation by
switching the internal high-side and low-side switch transistors. The transistor switches are pulse-width modulated at a fixed frequency of 2MHz. The high switching
frequency allows the use of a small inductor and output
capacitor, making the 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 1.0μA.
Applications
• Cellphones/Smartphones
• LED Photo Flash/Torch
• Mobile Handsets
The AAT1277 is available in a 18 ball 1.5mm x 2.4mm
CSP package.
Typical Application
L1 1μH
IN
VBAT
CIN
2.2μF
Movie Mode Enable
Flash Enable
Flash Inhibit
Flash LEDs
SW
OUT
AAT1277
MEN
FLEN
FLINH
FLOUTA
FLOUTB
CT
RMSET 169kΩ
RFSET 56.2kΩ
COUT
2.2μF
CT
47nF
MSET
FSET
AGND PGND FLGND
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
1
DATA SHEET
AAT1277
1.5A Step-Up Current Regulator for Flash LEDs
Pin Descriptions
Ball #
Symbol
A1
CT
A2
MEN
A3
FLEN
A4
AGND
A5
IN
A6, B3, B4
PGND
B1
FSET
B2, C2
B5, B6
FLGND
SW
C1
FLOUTA
C3
FLOUTB
C4
FLINH
C5
MSET
C6
OUT
Function
Flash timer control input. Connect a capacitor between CT and AGND to set maximum duration of the flash
pulse. A 47nF ceramic capacitor sets the flash timer to 375ms. To disable the flash timer, connect CT to
AGND.
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 200kΩ resistor to AGND.
Flash enable pin. A low-to-high transition on the FLEN pin initiates a flash pulse and starts the flash timer.
FLEN is an active high control input with a internal 200kΩ resistor to AGND.
Analog ground pin. Connect AGND to PGND and FLGND at a single point as close to AAT1277 as possible.
Power input. Connect IN to the input power supply voltage. Connect a 2.2μF or larger ceramic capacitor
from IN to PGND as close as possible to AAT1277.
Power ground pin. Connect PGND to AGND and FLGND at a single point as close to AAT1277 as possible.
Flash mode current setting input. A 56.2kΩ resistor from FSET to AGND sets the maximum flash current
available at FLOUTA and FLOUTB up to 1.5A total. Each FLOUTA and FLOUTB channel will conduct 50% of
the maximum programmed current
Flash ground pin. Connect FLGND to PGND and AGND at a single point as close to AAT1277 as possible
Boost converter switching node. Connect a 1μH inductor between SW and IN.
Flash Output A. Connect cathode of Flash LEDA to FLOUTA. For a single flash LED, connect FLOUTA and
FLOUTB together. For two flash LEDs, each output will conduct 50% of the total flash output current.
Flash Output B. Connect cathode of Flash LEDB to FLOUTB. For a single flash LED, connect FLOUTB &
FLOUTA together. For two flash LEDs, each output will conduct 50% of the total flash output current.
Flash inhibit pin. FLINH is an active high control input with an internal 200kΩ resistor to AGND. A low-tohigh 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 flash timer.
Movie mode current setting input. A 169kΩ 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.
Power output of the boost converter. Connect a 2.2μF 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)
2
6
A6
B6
C6
5
A5
B5
C5
4
A4
B4
C4
3
A3
B3
C3
2
A2
B2
C2
1
A1
B1
C1
A
B
C
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
DATA SHEET
AAT1277
1.5A Step-Up Current Regulator for Flash LEDs
Absolute Maximum Ratings1
(TA = 25°C unless otherwise noted.)
Symbol
IN, SW, OUT
MEN, FLEN, FLINH, CT, MSET, FSET
FLOUTA, FLOUTB
TJ
TA
Ts
TLEAD
Description
Maximum Rating
Maximum Rating
Maximum Rating
Junction Temperature Range
Operating Temperature Range
Storage Temperature Range
Maximum Soldering Temperature (at leads, 10 sec.)
Value
-0.3 to 6.0
VIN + 0.3
VOUT + 0.3
-40 to 150
-40 to 85
-65 to 150
300
Units
V
C
Thermal Information2
Symbol
θJA
PD
Description
Thermal Resistance
Maximum Power Dissipation3
Value
Units
105.5
940
C/W
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.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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3
DATA SHEET
AAT1277
1.5A Step-Up Current Regulator for Flash LEDs
Electrical Characteristics1
VIN = 3.6V; CIN = COUT = 2.2μF; L1 = 1μH; RFSET = 56.2kΩ; RMSET = 169kΩ; TA = -40°C to 85°C unless otherwise noted.
Typical values are at TA = 25°C.
Symbol
Description
Conditions
Power Supply
VIN
Input Voltage Range
Maximum Output Voltage
VOUT(MAX)
IIN(Q)
VIN Supply Current
ISHDN(MAX)
VIN Shutdown Current
IFL(TOTAL)
Total Output Current, Flash Mode
IFL
FLOUTA / FLOUTB Current Accuracy
IFL(MATCH)
FLOUTA / FLOUTB Current Matching Tolerance
IMM(LOAD)
Total Output Current, Movie Mode
fOSC
Oscillator Switching Frequency
tDEFAULT
Default ON Time
TSD
Thermal Shutdown Threshold
Thermal Shutdown Hysteresis
TSD(HYS)
FLEN/ MEN/FLINH Logic Control
VMEN(L),
VFLEN(L),
MEN, FLEN, FLINH Input Low Threshold
VFLINH(L)
VMEN(H),
MEN, FLEN, FLINH Input High Threshold
VFLEN(H),
VFLINH(H)
RIN(LOGIC)
FLINH, FLEN, MEN Input Resistance to AGND
FLEN ON Delay Time
tFLEN_ON
FLEN OFF Delay Time
tFLEN_OFF
tFLINH_ON
FLINH ON Delay Time
tFLINH_OFF
FLINH OFF Delay Time
Auto Disable Function2
VLED(DETECT)
Shorted LED Detection Voltage
ILED(DETECT)
Minimum LED Detection Current
Min
Typ
2.7
VFLEN = VIN, FL Load = 1.5A
VFLEN = VIN, FL Load = 0A
VMEN = VFLEN = VFLINH = GND
IFLOUTA + IFLOUTB
IMMOUTA + IMMOUTB
TA = 25°C
CT = 47nF
Max
Units
5.5
5.5
V
1.4
0.23
mA
1
1.2
-5
93
1.45
1.5
5
10
100
2.0
375
140
15
107
2.55
°C
0.4
1.4
100
VIN = 3V, ILED = 0.795μA
VIN = 3V
μA
A
%
%
mA
MHz
ms
V
V
200
200
10
93
5
1.45
795
kΩ
μs
V
μA
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 correlation with statistical process controls.
2. Guranteed by Design
4
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
PRODUCT
DATASHEET
DATA
SHEET
AAT1277
SwitchRegTM
1.5A Step-Up
Step-Up Current
Current Regulator
Regulator for
for Flash
Flash LEDs
LEDs
1.5A
Flash Mode Efficiency vs. Input Voltage
100
90
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
50
2.7
40
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
3.1
3.5
Shutdown Current vs. Input Voltage
4.7
5.1
5.5
Quiescient Current vs. Input Voltage
(VMEN = VFLEN = VFLINH = 0V)
( VFLEN = VIN; IFLOUTA = IFLOUTB = 0mA)
350
0.03
300
0.025
250
0.02
IIN(Q) (µA)
Shutdown Current (μA)
4.3
Input Voltage (V)
Input Voltage (V)
0.015
0.01
2.7
200
150
100
0.005
25°C
-40°C
3.1
3.5
3.9
4.3
4.7
5.1
85C
50
25C
-40C
0
0
5.5
2.7
3.1
3.5
Input Voltage (V)
1
0.5
0
-0.5
-1
-1.5
FL1
FL2
10
35
60
85
Output Current Accuracy (%)
2
1.5
-15
4.3
4.7
5.1
5.5
Flash and Movie Modes Current Matching
vs. Temperature
(VIN = 3.6V; IFLOUTA = IFLOUTB = 50mA)
-2
-40
3.9
Input Voltage (V)
Movie Mode Current Accuracy vs. Temperature
Output Current Accuracy (%)
3.9
(VIN = 3.6V)
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
Movie Mode
Flash Mode
-0.8
-40
-15
10
35
60
85
Temperature (°C)
Temperature (°C)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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5
PRODUCT
DATASHEET
DATA
SHEET
AAT1277
SwitchRegTM
1.5A Step-Up
Step-Up Current
Current Regulator
Regulator for
for Flash
Flash LEDs
LEDs
1.5A
Flash LED Current Accuracy vs. Temperature
Flash ON Delay Time vs. Input Voltage
(IFLOUTA = IFLOUTB = 750mA; COUT = 2.2μF; L = 1μH)
320
2
1.5
1
0.5
0
-0.5
-1
-1.5
FL1
FL2
-2
-40
-15
10
35
60
Flash ON Delay Time (μs)
Output Current Accuracy (%)
(VIN= 3.6V; IFLOUTA= IFLOUTB= 750mA)
280
240
200
160
120
80
85C
40
25C
-40C
0
85
2.7
3.1
3.5
Temperature (C)
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Flash ON Time vs. Input Voltage
Flash Timeout Delay vs. CT Capacitor
(IFLOUTA = IFLOUTB = 750mA; CT = 47nF; COUT = 2.2μF; L = 1μH)
(IFLOUTA = IFLOUTB = 750mA/ch; VIN = 3.6V)
440
1200
Flash Timeout (ms)
Flash ON Time (ms)
420
400
380
360
340
320
85C
300
1000
800
600
400
200
25C
-40C
280
2.7
3.1
3.5
3.9
4.3
4.7
5.1
0
0
5.5
20
40
Movie Mode LED Accuracy (%)
(IFLOUTA = IFLOUTB = 50mA; COUT = 2.2μF; L = 1μH)
10
8
6
4
2
0
-2
-4
-6
-8
3.1
3.5
3.9
4.3
Input Voltage (V)
6
100
120
140
4.7
5.1
5.5
Oscillator Frequency Accuracy vs. Temperature
Oscillator Frequency Accuracy (%)
Movie Mode Current Accuracy vs. Input Voltage
2.7
80
CT Capacitor (nF)
Input Voltage (V)
-10
60
(VIN = 3.6V; FOSC = 2MHz)
4
3
2
1
0
-1
-2
-3
-4
-40
-15
10
35
60
Temperature (°C)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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85
PRODUCT
DATASHEET
DATA
SHEET
AAT1277
SwitchRegTM
1.5A Step-Up
Step-Up Current
Current Regulator
Regulator for
for Flash
Flash LEDs
LEDs
1.5A
Oscillator Frequency (MHz)
Oscillator Frequency vs. Input Voltage
(TA = 25°C)
Flash Mode Output Ripple
(IFLOUT = 1.5A; VIN = 4V; L = 1μH)
2.4
2.3
VOUT
(AC Coupled)
(50mV/div)
2.2
2.1
2
VINDUCTOR
(2V/div)
1.9
0V
1.8
IINDUCTOR
(50mA/div)
1.7
1.6
2.7
3.1
3.5
3.9
4.3
4.7
5.1
1.65A
5.5
Time (200ns/div)
Input Voltage (V)
Movie Mode Line Transient
Movie Mode Turn On Characteristic
(IFLOUT = 206mA; VIN = 4.2V to 3.6V)
(IFLOUTA = IFLOUTB = 50mA; COUT = 2.2μF; VIN = 3.6V; L= 1μH)
VMEN
5V/div
4.2V
VIN
(500mV/div)
3.6V
VOUT
2V/div
VFLx
2V/div
IFL
(AC Coupled)
(50mA/div)
IFLx
100mA/div
0V
0V
0V
0A
Time (100μs/div)
Time (50μs/div)
Movie Mode to Flash Turn On Characteristic
Flash Turn On Characteristic
(IFLOUTA= IFLOUTB = 50mA to 750mA; COUT = 1.0uF; VIN = 3.6V; L= 1μH)
(IFLOUTA = IFLOUTB = 750mA; COUT = 2.2μF; VIN = 3.6V; L = 1μH)
VFLEN
5V/div
0V
VOUT
1V/div
3.0
VOUT
2V/div
0V
VFLx
2V/div
VFLx
1V/div
IFLx
1A/div
VFLEN
5V/div
IFLx
1A/div
0A
Time (100us/div)
0V
0V
0V
0V
Time (100us/div)
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
7
PRODUCT
DATASHEET
DATA
SHEET
AAT1277
SwitchRegTM
1.5A Step-Up
Step-Up Current
Current Regulator
Regulator for
for Flash
Flash LEDs
LEDs
1.5A
Flash Inhibit Turn On Characteristic
Flash Mode Timing
(IFLOUTA = IFLOUTB = 750mA to 50mA; COUT = 2.2μF; VIN = 3.6V; L = 1μH)
(IFLOUTA = IFLOUTB = 750mA; COUT = 2.2μF; VIN = 3.6V; L = 1μH)
VFLEN
5V/div
VFLEN
5V/div
0V
VOUT
1V/div
3.3
VOUT
2V/div
VFLx
1V/div
0V
VFLx
2V/div
0A
IFLx
1A/div
IFLx
1A/div
0V
0V
0V
0V
Time (100ms/div)
Time (100us/div)
Movie Mode Ripple
MEN, FLEN, FLINH Logic Threshold
High vs Input Voltage
(IFLOUTA = IFLOUTB = 50mA; COUT = 2.2μF; VIN = 3.1V; L = 1μH)
1.2
1.1
VSW
2V/div
ISW
200mA/div
VMEN, VFLEN, VFLNH (V)
VOUT
20mV/div
AC Coupling
0V
0A
1
0.9
0.8
0.7
0.6
25C
0.5
85C
-40C
0.4
2.7
3.1
3.5
Time (500ns/div)
4.3
4.7
5.1
5.5
Input Voltage (V)
MEN, FLEN, FLINH Logic Threshold
Low vs Input Voltage
MEN, FLEN, FLINH Input Pull Down
Resistance vs Temperature
1.2
400
1.1
350
RMEN, RFLEN, RFLNH (kΩ)
VMEN, VFLEN, VFLNH (V)
3.9
1
0.9
0.8
0.7
0.6
25C
0.5
85C
300
250
200
150
100
50
-40C
0.4
2.7
0
3.1
3.5
3.9
4.3
Input Voltage (V)
8
4.7
5.1
5.5
-40
-15
10
35
60
Temperature (°C)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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85
DATA SHEET
AAT1277
1.5A Step-Up Current Regulator for Flash LEDs
Functional Block Diagram
IN
OUT
SW
FLOUTA
FLOUTB
MEN
FLEN
Control
FLINH
MSET FSET CT
Functional Description
The AAT1277 is a boost converter with a current regulated 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 malfunction 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 recommended 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
AGND PGNDFLGND
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 application, the two current sources can be connected together to apply full output current into the LED. In two LED
applications, each diode can be connected to its corresponding current source (FLOUTA or FLOUTB) and the
output current will be shared. In applications where only
one LED is connected to either FLOUTA or FLOUTB, the
unused current sink must be directly connected to OUT,
thereby disabling that channel.
Flash Inhibit Function
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 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.
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
9
DATA SHEET
AAT1277
1.5A Step-Up Current Regulator for Flash LEDs
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 current 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 illumination.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 overvoltage protection (OVP) circuitry, which prevents damage to the AAT1277 from open LED or open circuit conditions. During an open circuit, the output voltage rises
and reaches 5.5V (typical), and the OVP circuit disables
the switching, preventing the output voltage from rising
higher. Once the open circuit condition is removed,
switching will resume 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
OFF
t= 0
t= n
Figure 1: Movie Mode Timing Diagram.
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
DATA SHEET
AAT1277
1.5A Step-Up Current Regulator for Flash LEDs
MEN
FLEN
IFLOUTA = IFLOUTA = IFL
OFF
t = t CT
t= 0
Figure 2: Diagram of Flash Mode When Flash Event Does Not Exceed Flash Timer TFLASH < TCT.
MEN
FLEN
IFLOUTA = IFLOUTA = IFL
OFF
t= 0
t = t CT
Figure 3: Diagram of Flash Mode Timing When Flash Event is Terminated by Flash Timer TFLASH ≥ TCT.
MEN
FLEN
IFLOUTA = IFLOUTA = IFL
IFLOUTA = IFLOUTA = IMM
OFF
MM=ON
t= 0
t = t CT
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.
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11
DATA SHEET
AAT1277
1.5A Step-Up Current Regulator for Flash LEDs
MEN
FLEN
IFLOUTA = IFLOUTA = IFL
IFLOUTA = IFLOUTA = IMM
OFF
MM = ON
t= 0
t = t CT
Flash
Timer
Reset
Next
Flash
Event
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.)
MEN
FLEN
FLINH
IFLOUTA = IFLOUTA = IFL
IFLOUTA = IFLOUTA = IMM
OFF
MM=ON
t=0
t = t CT
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).
12
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DATA SHEET
AAT1277
1.5A Step-Up Current Regulator for Flash LEDs
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 maximum 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:
RFSET =
56.2kΩ · 750mA
IFLOUTX
A flash event is initiated by asserting the FLEN pin. A
flash event is automatically terminated when FLEN is deasserted 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 moviemode current level will be maintained on FLOUTA and
FLOUTB as long as the FLINH and FLEN pins are asserted, and the safety timer continues to run.
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 eliminates 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 equation:
T = 7.98s/μF · CT (μF)
Where T is in seconds and CT is in μF.
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.
1200
Flash Timeout (ms)
Applications Information
1000
800
600
400
200
0
0
20
40
60
80
100
120
140
CT Capacitor (nF)
Figure 7: Flash Safety Timeout
vs. Timer Capacitor.
Movie Mode Current
The AAT1277 movie mode current settings can be programmed by the external resistor RMSET.
169kΩ · 50mA
RMSET =
IMMOUTX
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
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.
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13
DATA SHEET
AAT1277
1.5A Step-Up Current Regulator for Flash LEDs
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 1μH inductor
is recommended. Manufacturer’s specifications list both
the inductor DC current rating, which is a thermal limitation, and peak inductor current rating, which is determined by the saturation characteristics. Measurements
at full load and high ambient temperature should be performed to ensure that the inductor does not saturate or
exhibit excessive temperature rise.
The inductor (L) is selected to avoid saturation at minimum input voltage and maximum output load conditions.
Worst-case peak current occurs at minimum input voltage (maximum duty cycle) and maximum load. Bench
measurements are recommended to confirm actual IPEAK
and to ensure that the inductor does not saturate at
maximum LED current and minimum input supply voltage. The RMS current flowing through the boost inductor
is equal to the DC plus AC ripple components. Under
worst case RMS conditions, the current waveform is
critically continuous. The resulting RMS calculation yields
worst case inductor loss. The RMS current value should
be compared against the inductor manufacturer’s temperature rise, or thermal derating guidelines:
IRMS =
IPEAK
3
For a given inductor type, smaller inductor size leads to
an increase in DCR winding resistance and, in most
cases, increased thermal impedance. Winding resistance
degrades boost converter efficiency and increases the
inductor’s operating temperature:
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 1μF ceramic output capacitor is recommended
(see Table 2). Typically, 6.3V or 10V rated capacitors are
required for this flash LED boost output. Ceramic capacitors selected as small as 0603 are available which meet
these requirements. MLC capacitors exhibit significant
capacitance reduction with applied voltage. Output ripple
measurements should confirm that output voltage drop
and operating stability are within acceptable limits.
Voltage derating can minimize this factor, but results may
vary with package size and among specific manufacturers. To maintain stable operation at full load, the output
capacitor should be selected to maintain ∆VOUT between
100mV and 200mV. The boost converter input current
flows during both ON and OFF switching intervals. The
input ripple current is less than the output ripple and, as
a result, less input capacitance is required.
PCB Layout Guidelines
Boost converter performance can be adversely affected
by poor layout. Possible impact includes high input and
output voltage ripple, poor EMI performance, and
reduced operating efficiency. Every attempt should be
made to optimize the layout in order to minimize parasitic PCB effects (stray resistance, capacitance, and
inductance) and EMI coupling from the high frequency
SW node. A suggested PCB layout for the AAT1277 1.5A
step-up regulator is shown in Figures 4 and 5. The following PCB layout guidelines should be considered:
1.
PLOSS(INDUCTOR) = I2RMS · 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 2.2μF 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 AAT1277
boost regulator. MLC capacitors of type X7R or X5R are
14
2.
3.
4.
5.
Minimize the distance from capacitor CIN and COUT’s
negative terminals to the PGND pins. This is especially true with output capacitor COUT, which conducts
high ripple current from the output to the PGND
pins.
Minimize the distance under the inductor between IN
and switching pin SW; minimize the size of the PCB
area connected to the SW pin.
Maintain a ground plane and connect to the IC PGND
pin(s) as well as the PGND connections of CIN and
COUT.
Consider additional PCB exposed area for the flash
LEDs to maximize heatsinking capability. This may
be necessary when using high current application
and long flash duration application.
Connect the exposed paddle (bottom of the die) to
either PGND or GND. Connect AGND, FLGND to GND
as close as possible to the package.
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DATA SHEET
AAT1277
1.5A Step-Up Current Regulator for Flash LEDs
Manufacturer
Part Number
Inductance
(μH)
Saturated Rated
Current (A)
DCR
(mΩ)
Size (mm)
LxWxH
Cooper Bussmann
Cooper Bussmann
Cooper Bussmann
Sumida
Coilcraft
SD3812-1R0-R
SDH3812-1R0-R
SD10-1R0-R
CDH38D11/S
LPS4012-102NLC
1
1
1
1
1
2.69
3
2.25
2.8
2.5
48
45
44.8
48.8
60
4.0x4.0x1.2
3.8x3.8x1.2
5.2x5.2x1.0
4.0x4.0x1.2
4.1x4.1x1.2
Type
Shielded
Shielded
Shielded
Shielded
Shielded
Drum
Drum
Drum
Drum
Drum
Core
Core
Core
Core
Core
Table 1: Typical Suggested Surface Mount Inductors.
Manufacturer
Murata
Part Number
Capacitance (μF)
Voltage Rating (V)
Temp Co.
Case Size
GRM185R60J225KE26
GRM188R71A225KE15
GRM21BR70J225KA01
GRM21BR71A225KA01
GRM219R61A475KE19
2.2
2.2
2.2
2.2
4.7
6.3
10
6.3
10
10
X5R
X7R
X7R
X7R
X5R
0603
0603
0805
0805
0805
GRM21BR71A106KE51
10
10
X7R
0805
Table 2: Typical Suggested Surface Mount Capacitors.
*Denotes the default value.
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15
DATA SHEET
AAT1277
1.5A Step-Up Current Regulator for Flash LEDs
VIN
J1
VIN
SW1
1
3
R3
2
4
100k
FLINH
J2
SW2
1
3
R4
100k
VIN
2
4
FLEN
J3
VIN
SW3
1
3
R5
JP1
0
JP2
0
D1
D2
100k
VIN
U1
2
4
A1
A2
A3
A4
A5
B5, B6
A6, B3, B4
MEN
L1 1μH
C4
1μF
VOUT
C1
2.2μF
CT
FSET
MEN FLOUTA
FLEN
FLGND
AGND FLOUTB
IN
FLINH
SW
MSET
PGND
OUT
AAT1277 CSP-18
C3
47nF
GND
D1, D2
L1
C1, C2
C3
B1
C1
B2, C2
C3
C4
C5
C6
R2
169k
R1
56.2k
C2
2.2μF
Seoul Semi FOW401-Z4S
CooperBussmann SD3812-1R0-R, 1μH, 2.69A, 48mΩ
Murata GRM188R71A225KE15 2.2μF, 0603, X7R, 10V
Murata GRM155R71A473KA01, 47nH, 0402, X7R, 10V
Figure 8: AAT1277 Evaluation Board Schematic.
Figure 9: AAT1277 Evaluation Board
Top Side Layout.
16
Figure 10: AAT1277 Evaluation Board
Bottom Side Layout.
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DATA SHEET
AAT1277
1.5A Step-Up Current Regulator for Flash LEDs
Component
Part Number
U1
AAT1277IUT
SW1 – SW3
R1
R2
R3, R4, R5
JP1, JP2
C1, C2
C3
L1
D1-D2
PTS645TL50
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
GRM188R71A225KE15
GRM155R71A473KA01
SD3812-1R0-R
LXCL-PWF4
Description
1.5A Step-Up Current Regulator for Flash LEDs;
18 ball 1.5mm x 2.4mm CSP package
Switch, SPST, 5mm
56.2kΩ, 1%, 1/4W; 0402
169kΩ, 1%, 1/4W; 0402
100kΩ, 1%, 1/4W; 0603
0Ω, 5%, 1/4W; 0603
2.2μF, 10V, X7R, 0603
47nF, 10V, X7R, 0402
Drum Core, 1μH, 2.69A, 48mΩ
White Flash LED
Manufacturer
Skyworks
ITT Industries
Vishay
Vishay
Vishay
Vishay
Murata
Murata
Cooper Bussmann
Lumileds, Philips
Table 3: AAT1277 Evaluation Board Bill of Materials.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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17
DATA SHEET
AAT1277
1.5A Step-Up Current Regulator for Flash LEDs
Ordering Information
Package
Marking1
Part 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.
18
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DATA SHEET
AAT1277
1.5A Step-Up Current Regulator for Flash LEDs
Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved.
Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. These materials, including the information contained herein, are provided by Skyworks as a
service to its customers and may be used for informational purposes only by the customer. Skyworks assumes no responsibility for errors or omissions in these materials or the information contained herein. Skyworks may change its documentation, products, services, specifications or product descriptions at any time, without notice. Skyworks makes no commitment to update the materials or information and shall have no
responsibility whatsoever for conflicts, incompatibilities, or other difficulties arising from any future changes.
No license, whether express, implied, by estoppel or otherwise, is granted to any intellectual property rights by this document. Skyworks assumes no liability for any materials, products or information provided hereunder, including the sale, distribution, reproduction or use of Skyworks products, information or materials, except as may be provided in Skyworks Terms and Conditions of Sale.
THE MATERIALS, PRODUCTS AND INFORMATION ARE PROVIDED “AS IS” WITHOUT WARRANTY OF ANY KIND, WHETHER EXPRESS, IMPLIED, STATUTORY, OR OTHERWISE, INCLUDING FITNESS FOR A PARTICULAR
PURPOSE OR USE, MERCHANTABILITY, PERFORMANCE, QUALITY OR NON-INFRINGEMENT OF ANY INTELLECTUAL PROPERTY RIGHT; ALL SUCH WARRANTIES ARE HEREBY EXPRESSLY DISCLAIMED. SKYWORKS DOES
NOT WARRANT THE ACCURACY OR COMPLETENESS OF THE INFORMATION, TEXT, GRAPHICS OR OTHER ITEMS CONTAINED WITHIN THESE MATERIALS. SKYWORKS SHALL NOT BE LIABLE FOR ANY DAMAGES, INCLUDING BUT NOT LIMITED TO ANY SPECIAL, INDIRECT, INCIDENTAL, STATUTORY, OR CONSEQUENTIAL DAMAGES, INCLUDING WITHOUT LIMITATION, LOST REVENUES OR LOST PROFITS THAT MAY RESULT FROM
THE USE OF THE MATERIALS OR INFORMATION, WHETHER OR NOT THE RECIPIENT OF MATERIALS HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
Skyworks products are not intended for use in medical, lifesaving or life-sustaining applications, or other equipment in which the failure of the Skyworks products could lead to personal injury, death, physical or environmental damage. Skyworks customers using or selling Skyworks products for use in such applications do so at their own risk and agree to fully indemnify Skyworks for any damages resulting from such improper
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Customers are responsible for their products and applications using Skyworks products, which may deviate from published specifications as a result of design defects, errors, or operation of products outside of published parameters or design specifications. Customers should include design and operating safeguards to minimize these and other risks. Skyworks assumes no liability for applications assistance, customer product
design, or damage to any equipment resulting from the use of Skyworks products outside of stated published specifications or parameters.
Skyworks, the Skyworks symbol, and “Breakthrough Simplicity” are trademarks or registered trademarks of Skyworks Solutions, Inc., in the United States and other countries. Third-party brands and names are for
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