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AAT1274 Schematic ( PDF Datasheet ) - Skyworks Solutions

Teilenummer AAT1274
Beschreibung 1.5A Single Flash LED Driver IC
Hersteller Skyworks Solutions
Logo Skyworks Solutions Logo 




Gesamt 17 Seiten
AAT1274 Datasheet, Funktion
DATA SHEET
AAT1274
1.5A Single Flash LED Driver IC
General Description
The AAT1274 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 AAT1274 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
AAT1274. 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
AAT1274 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 AAT1274
can drive one high current LED.
The AAT1274 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 AAT1274 is available in a Pb-free, thermally-enhanced
TDFN33-14 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
• 2 MHz 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
• TDFN33-14 Package
Applications
• LED Photo Flash / Torch
• Camera Enabled Mobile Devices
• Cellphones/Smartphones
• Digital Still Cameras (DSCs)
• Multimedia Mobile Phones
Typical Application
L1 1μH
VBAT = 2.7V to 5.5V
Enable/Set Input
Flash Enable
Flash Inhibit
CIN
2.2μF
IN
SW
OUT
AAT1274
EN/SET
FL
COUT
2.2μF
Flash LED
FLEN
FLINH
RSET
RSET
PGND AGND FLGND
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
201981A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 21, 2012
1






AAT1274 Datasheet, Funktion
Typical Characteristics
Movie Mode LED Current Accuracy vs. Input Voltage
(IFL = 206mA; L = 1µH)
10
8
6
4
2
0
-2
-4
-6
-8
-10
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
Input Voltage (V)
Flash Mode Output Ripple
(IFL = 1.5A; VIN = 4V; L = 1µH)
VOUT
(AC Coupled)
(50mV/div)
VINDUCTOR
(2V/div)
0V
IINDUCTOR
(50mA/div)
1.65A
Time (200ns/div)
Flash On Time Delay vs. Input Voltage
(IFL = 1.5A; COUT = 2.2µF; L = 1µH)
80
70
60
50
40
30
20 -40°C
10 25°C
85°C
0
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
Input Voltage (V)
DATA SHEET
AAT1274
1.5A Single Flash LED Driver IC
Movie Mode Output Ripple
(IFL = 206mA; VIN = 3.6V; L = 1µH)
VOUT
(AC Coupled)
(50mV/div)
VINDUCTOR
(2V/div)
0V
IINDUCTOR
(100mA/div)
100mA
Time (500ns/div)
Flash LED Current vs. Temperature
(IFL = 1.5A; VIN = 4.2V; L = 1µH)
1580
1560
1540
1520
1500
1480
1460
1440
1420
-40 -15 10 35 60
Temperature (°C)
85
Movie Mode Line Transient
(IFL = 206mA; VIN = 4.2V to 3.6V)
VIN
(500mV/div)
IFL
(AC Coupled)
(50mA/div)
4.2V
3.6V
Time (50µs/div)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
6 201981A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 21, 2012

6 Page









AAT1274 pdf, datenblatt
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
1*
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Percentage of Maximum MM Current
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 1:2 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 1 to 7.3. The default maximum movie mode current
can be calculated:
IMOVIE MODE
=
IFL(MAX)
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
7.3
= 206mA
DATA SHEET
AAT1274
1.5A Single Flash LED Driver IC
The maximum movie mode current level can be calcu-
lated using the following equation:
IMOVIE MODE
=
107kΩ ×
RSET
A
=
FL
to
1
MM
Ratio
=
Max
Movie
Mode
Current
Data
1
2
3
4*
5
6
7
8
9
10
11
12
13
14
15
16
Flash to Movie Mode Ratio
½
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
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 AAT1274 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 AAT1274 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 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.
* Denotes the default value.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
12 201981A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 21, 2012

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