AAT1282 Datasheet, PDF (15/22 Pages) Skyworks Solutions Inc. – 2A Driver for High Intensity LED Camera Flash

DATA SHEET
AAT1282
2A Driver for High Intensity LED Camera Flash
Register 1 (REG1); Register Address: 01h
Bits [5:4] Program the FLOUTA and FLOUTB with four ON/OFF configurations.
Bits [3:0] Program the flash-to-movie mode ratio with 16 different fractions from the hardware configuration, RSET.
MSB
X
X
LSB
5
4
3
2
1
0
Flash-to-Movie
Mode Ratio
0000 = 1/2
0001 = 1/3.8
0010 = 1/5.5
0011 = 1/7.3 (default)
0100 = 1/8.9
0101 = 1/10.5
0110 = 1/12.2
0111 = 1/13.8
1000 = 1/14.9
1001 = 1/16.5
1010 = 1/18
1011 = 1/19.6
1100 = 1/21.1
1101 = 1/22.6
1110 = 1/24
1111 = OFF
FLOUTA FLOUTB
00 OFF OFF (default)
01 OFF* ON
10 ON
OFF*
11 ON
ON
*with 2-3mA standby current
Figure 7: AAT1282 Register 1 Programming.
Selecting the Boost Inductor
The AAT1282 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.
The inductor (L) is selected to avoid saturation at mini-
mum input voltage and maximum output load conditions.
Worst-case peak current occurs at minimum input volt-
age (maximum duty cycle) and maximum load. Bench
measurements are recommended to confirm actual I_PEAK
and to ensure that the inductor does not saturate at
maximum LED current and minimum input supply volt-
age. The RMS current flowing through the boost inductor
is equal to the DC plus AC ripple components. Under
worst case RMS conditions, the current waveform is
critically continuous. The resulting RMS calculation yields
worst case inductor loss. The RMS current value should
be compared against the inductor manufacturer’s tem-
perature rise, or thermal derating guidelines:
I_RMS = ^IPEAK
3
For a given inductor type, smaller inductor size leads to
an increase in DCR winding resistance and, in most
cases, increased thermal impedance. Winding resistance
degrades boost converter efficiency and increases the
inductor’s operating temperature:
P_{LOSS(INDUCTOR)} = I^2RMS · DCR
Selecting the Boost Capacitors
In general, it is good design practice to place a decou-
pling capacitor (input capacitor) between the IN and GND
pins. An input capacitor in the range of 2.2μF to 10μF is
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
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