AAT1282 Datasheet, PDF (16/22 Pages) Skyworks Solutions Inc. – 2A Driver for High Intensity LED Camera Flash

DATA SHEET
AAT1282
2A Driver for High Intensity LED Camera Flash
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 pro-
vide small size and adequate capacitance, low parasitic
equivalent series resistance (ESR) and equivalent series
inductance (ESL), and are well suited for use with the
AAT1282 boost regulator. MLC capacitors of type X7R or
X5R are recommended to ensure good capacitance sta-
bility over the full operating temperature range. The out-
put capacitor is selected to maintain the output load
without significant voltage droop (∆V_OUT) during the
power switch ON interval. A ceramic output capacitor
2.2μF 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 droop and operating stability are within
acceptable limits. Voltage derating can minimize this fac-
tor, 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 main-
tain ∆V_OUT between 100mV and 200mV. The boost con-
verter 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.
Super Capacitor
The AAT1282 requires a super capacitor connected to
the output and the LEDs. After the super capacitor is
fully charged, sufficient energy is stored and ready to
provide large power surges such as flash peak current.
When selecting a super capacitor, it is highly recom-
mended to select a capacitor with an operating voltage
of 5.5V and 500mF DC capacitance for the best results
in AAT1282 camera flash applications. Low profile, low
impedance (low ESR below 110mΩ), and a wide environ-
mental operating range (-40°C to +85°C) should also be
considered when selecting a capacitor for portable power
management systems. Please contact the super capaci-
tor manufacturer(s) (such as TDK, CAP-XX or Murata) for
detailed information.
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 AAT1282 High Power 2A
Flash LED driver is shown in Figures 8 through 11. The
following PCB layout guidelines should be considered:
1. Minimize the distance from capacitor C_IN and C_OUT’s
negative terminals to the PGND pins. This is espe-
cially true with output capacitor C_OUT, which conducts
high ripple current from the output to the PGND
pins.
2. Minimize the distance between IN and switching pin
SW; minimize the size of the PCB area connected to
the SW pin.
3. Maintain a ground plane and connect to the IC PGND
pin(s) as well as the PGND connections of C_IN and
C_OUT.
4. 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.
5. 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.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
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202305C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013