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PDF AAT1282 Data sheet ( Hoja de datos )
| Número de pieza | AAT1282 | |
| Descripción | 2A Driver for High Intensity LED Camera Flash | |
| Fabricantes | Skyworks Solutions | |
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DATA SHEET
AAT1282
2A Driver for High Intensity LED Camera Flash
General Description
The AAT1282 is a high-efficiency, high-current step-up
converter capable of 2A maximum output current. It is
an ideal power solution for LED photo flash applications
in all single cell Li-ion powered products.
The AAT1282 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 AAT1282 ideally suited
for small battery-powered applications. A high-capacity
Super Capacitor on the secondary side of the step-up
converter provides the high-peak flash LED current,
thereby reducing the peak current demand from the
Li-ion battery. To achieve this, the step-up converter
features a fixed, input current limiter.
An industry-standard I2C serial digital input is used to
enable, disable and set the movie-mode current for each
flash LED with up to 16 movie-mode settings. The
AAT1282 also includes a separate Flash Enable input to
initiate both the flash operation and the default timer
which can be used either to terminate a flash event at the
end of a user-programmed delay or as a safety feature.
The maximum flash and movie-mode current is set by
one external resistor where the ratio between Flash to
Movie-mode current is set at approximately 7.3:1. One or
two LEDs can be connected to the AAT1282, where in the
case of two LEDs the output current is matched between
each diode. The ratio of maximum flash current to movie-
mode current can also be adjusted via the I2C control.
The AAT1282 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 AAT1282 is available in a Pb-free, thermally-
enhanced 14-pin 3 x 3mm TDFN package.
Features
VIN Range: 2.7V to 5.5V
Dual Channel Output
▪ Up to 2A Regulated Output Current
1A per channel
Integrated Fixed Input Current Limit
▪ 800mA*
▪ Suited for Super Capacitor Applications
Up to 80% Efficiency with Small Magnetics
2MHz Switching Frequency
Independent Flash Enable
User-programmable Safety Timer
Single Resistor Sets Flash and Movie-mode Current
Two Wire, I2C Compliant Serial Interface:
▪ Fast, 400kHz Serial Transfer Rate
▪ 16 level Movie-mode Current
▪ Flash/Movie-mode
▪ Current Output Channel Control
▪ Safety Timer
• True Load Disconnect
• Supply Current in Shutdown: <1.0μA
• TDFN33-14 Package
Applications
• Camcorder Video Light (Torch Light)
• Camera Phones/Smartphones
• Digital Still Cameras (DSC)
• LED Photo Flash Light (Strobe Light)
• Mobile Handsets
* Contact Sales for alternative current limits.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202305C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013
1
1 page  
I2C Interface Timing Details
DATA SHEET
AAT1282
2A Driver for High Intensity LED Camera Flash
SDA
SCL
TLOW
TSU_DAT
THD_STA
THD_DAT
THIGH
TSU_STA
THD_STA
TSU_STO
TBUF
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202305C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013
5
5 Page 
DATA SHEET
AAT1282
2A Driver for High Intensity LED Camera Flash
Applications Information
LED Selection
The AAT1282 is specifically designed to drive ultra bright
flash LEDs with typical forward voltage of 2.5V to 4.0V
within 1A forward current. Since the FLOUTA and FLOUTB
pins have internal current-mirror circuitry which matches
both channels with tight accuracy up to 1A per channel;
the LED-to-LED brightness will be matched regardless of
the individual LED forward voltage (VF). Circuit designers
should consult the LED supplier for LED specifications.
Flash Mode LED Current
The LED current is controlled by the RSET resistor. For
maximum accuracy, a 1% tolerance resistor is recom-
mended. FLOUTA and FLOUTB can be programmed up to
a maximum total flash current of 2000mA or up to
1000mA per channel. FLOUTA and FLOUTB output current
is matched across the programming range. A flash event
is initiated by asserting the FLEN pin. A flash event is
automatically terminated when FLEN is disabled or if the
safety timer terminates before the FLEN pin is disabled.
The maximum flash current in each FLOUTA and FLOUTB
is set by the RSET resistor and can be calculated using the
following equation:
81kΩ · A 81kΩ · A
IFLOUTA = IFLOUTB = RSET
= = ~1000mA per channel
80.6kΩ
To prevent excessive power dissipation during higher
flash current operation, RSET values smaller than 80.6kΩ
are not recommended.
Since the super capacitor is the only source for the LED
flash current, the duration of the flash is determined by
the energy stored in the super capacitor. During flash,
the energy of the super capacitor is discharged; at the
same time, the voltage of the super capacitor is
decreased. Once the super capacitor voltage is lowered
to a level (the minimum sink pin voltage + the LED
forward voltage), the flash is ended. With a fully charged
super capacitor in place, the flash for two 1A LEDs can
last for more than 500ms.
Movie Mode LED Current
The maximum movie-mode current level is set by the
maximum, programmed flash current reduced by the
programmed flash-to-movie-mode ratio in which the
default value is 7.3:
I =MOVIE-MODE[A/B]
I =FLOUT[A/B](MAX)
7.3
1000mA
7.3
= 137mA
To change the configuration or the settings, the AAT1282
can be programmed via the I2C interface. Triggering the
FLEN low to high will enable a flash event with the
maximum flash current set by the RSET resistor or with
programmed flash current set via the I2C interface.
Concurrently, the flash timer is also initiated. All data
and register contents are cleared (reset to the default
value) after each flash event.
Flash Safety Timeout
The AAT1282 includes a timer circuit that enables the
flash current for a programmed period of time. This fea-
ture eliminates the need for an external, 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 con-
troller’s flash software routine experiences hang-up or
freeze. The flash safety timeout, T can be calculated by
the following equation:
T = 13.5s/μF · CT
Where T is in seconds and CT is the capacitance of the
timer capacitor in μF.
For example, using a 74nF capacitor for CT sets the flash
timeout to:
Flash Safety Timeout = 13.5s/μF · 0.074μF = 1s
The relationship between the flash safety timeout and
the capacitance of the timer capacitor is illustrated in
Figure 1.
1200
1000
800
600
400
200
0
0 10 20 30 40 50 60 70 80 90
CT Capacitor (nF)
Figure 1: Flash Safety Timeout
vs. Timer Capacitor.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202305C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013
11
11 Page | ||
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| PDF Descargar | [ Datasheet AAT1282.PDF ] | |
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