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AAT1270 Schematic ( PDF Datasheet ) - AAT

Teilenummer AAT1270
Beschreibung 1A Step-Up Current Regulator
Hersteller AAT
Logo AAT Logo 




Gesamt 18 Seiten
AAT1270 Datasheet, Funktion
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 Datasheet, Funktion
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 pdf, datenblatt
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





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