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Teilenummer | AAT1270 |
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Beschreibung | 1A Step-Up Current Regulator | |
Hersteller | AAT | |
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Gesamt 18 Seiten www.DataSheet4U.com
AAT1270
1A Step-Up Current Regulator for Flash LEDs
General Description
SwitchReg™
The AAT1270 is a high-efficiency, high-current boost
converter capable of 1A maximum output current. It
is an ideal power solution for LED photo flash appli-
cations in all single-cell Lithium-ion / polymer battery
operated products.
The AAT1270 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 induc-
tor and output capacitor, making the AAT1270 ideal-
ly suited for small battery-powered applications.
AnalogicTech’s proprietary S2Cwire™ (Simple Serial
Control™) serial digital interface is used to enable,
disable and set the movie mode current level for the
flash LEDs to one of 16 levels. The AAT1270 also
includes a separate Flash Enable input to initiate both
flash/strobe operation and the default timer, which
can be used to terminate a flash event after a user-
programmed delay or as a safety feature. A Flash
Inhibit pin is also included which reduces flash cur-
rent to movie mode level during high battery demand.
The maximum flash and movie mode current is set
by one external resistor; the ratio between flash and
movie mode current is set at approximately 7.3:1.
One or two LEDs can be connected to the AAT1270;
when two LEDs are used, the output current is
matched between each diode.
The AAT1270 contains over-voltage protection and a
thermal management system to protect the device in
the event of an output open-circuit and short-circuit
condition respectively. Built-in circuitry prevents exces-
sive inrush current during start-up. The shutdown fea-
ture reduces quiescent current to less than 1.0µA.
Typical Application
The AAT1270 is available in a Pb-free, thermally-
enhanced 14-pin 3x3mm STDFN package.
Features
• Input Voltage Range: 2.7V to 5.5V
• Dual Channel Output
— Up to 1A Regulated Output Current
(0.5A per Channel)
• Up to 85% Efficiency with Small Magnetics
• 2 MHz Switching Frequency
• Separate Flash Enable Input
• Separate Flash Inhibit Input
• Single Resistor Sets Flash and Movie Mode Current
— Fixed Flash-to-Movie Mode Current Ratio
• 16-Level Movie Mode Current via S2Cwire™
• User-Programmable Safety Timer
• True Load Disconnect
• Input Current Limit
• Over-Voltage (Open LED, Open Circuit), Short-
Circuit, and Over-Temperature Protection
• Shutdown Current: < 1.0µA
• Small Inductor Solution: 1µH (0.9mm in height)
• 14-pin STDFN 3x3 Package
• -40 to +85°C Temperature Range
Applications
• Camcorder Video Light (Torch Light)
• Cellphones / Smartphones
• Digital Still Cameras (DSC)
• LED Photo Flash Light (Strobe Light)
• Mobile Handsets
• MP3 Players
• PDAs and Notebook PCs
L1
1μH
VBATTERY
Movie Mode
Enable and Set
Flash Enable
Flash Inhibit
CIN
2.2μF
RSET
162kΩ
IN SW
OUT
AAT1270
EN/SET
FLEN
FLINH
FLOUTA
FLOUTB
RSET
CT
GND AGND PGND FLGND
Flash LEDs
Lumiled LXCL-PWF1 or equivalent
COUT
2.2μF
CT
47nF
1270.2007.07.1.0
1
AAT1270
1A Step-Up Current Regulator for Flash LEDs
Typical Characteristics
Flash Mode Output Ripple
(500mA/ch)
3.4
3.2
3.0
4V
0V
Time (250ns/div)
2.5
2.0
1.5
Movie Mode Output Ripple
(68.5mA/ch)
3.20
3.18
3.16
3.2V
0V
0.4
0.2
0.0
Time (125ns/div)
EN/SET, FLEN Input High Threshold
vs. Input Voltage
1.2
-40°C
1.0
0.8
0.6 85°C
25°C
0.4
0.2
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
Input Voltage (V)
EN/SET, FLEN Input Low Threshold
vs. Input Voltage
1.2
-40°C
1.0
0.8
0.6 25°C
85°C
0.4
0.2
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
Input Voltage (V)
EN/SET Latch Timeout vs. Input Voltage
450
400 -40°C
350 85°C
300 25°C
250
200
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
Input Voltage (V)
EN/SET Off Timeout vs. Input Voltage
550
500 -40°C
450
400
350 25°C
300
85°C
250
200
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
Input Voltage (V)
6 1270.2007.07.1.0
6 Page AAT1270
1A Step-Up Current Regulator for Flash LEDs
Flash Timer
The AAT1270A includes a timer circuit that enables
the flash current sinks for a programmed period of
time. This feature eliminates the need for an exter-
nal, housekeeping baseband controller to contain a
safety delay routine. It also serves as a protection
feature to minimize thermal issues with the flash
LEDs in the event an external controller’s flash soft-
ware routine experiences hang-up or freeze.
The flash timeout T can be calculated by the fol-
lowing equation:
T = 21.5s/µF · CT
Where T is in seconds and CT is the capacitance of
the timer capacitor in µF.
For example, using a 47nF capacitor for CT sets
the flash timeout to:
Flash Timeout = 21.5s/µF · 0.047µF = 1s
The relationship between capacitance of the timer
capacitor and the flash timeout is illustrated in
Figure 2.
50
45
40
35
30
25
20
15
10
5
0
0 100 200 300 400 500 600 700 800 900 1000
Flash Timeout (ms)
Figure 2: Timer Capacitor vs. Flash Timeout.
Timing Diagram
FLASH FLASH
MOVIE MODE
LED CURRENT (0mA)
FLASH LOWERED
TO MOVIE-MODE
DURING FLINH
FLASH
EN/SET
DATA TO
MOVIE-MODE
LEVEL
FLASH
FLASH
tDLY(CT)
FLASH TIMES OUT
tDLY(CT)
FLASH TIMES OUT
SET BY CT
FLASH LOWERED
TO MOVIE-MODE
DURING FLINH
FLASH ENABLE
FLASH INHIBIT
12
1270.2007.07.1.0
12 Page | ||
Seiten | Gesamt 18 Seiten | |
PDF Download | [ AAT1270 Schematic.PDF ] |
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