PRODUCT DATASHEET
AAT1272
TM
SwitchReg
1.5A Step-Up Current Regulator for Flash LEDs
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
LSB
0
X
5
4
3
2
1
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
01
10
11
OFF
OFF*
ON
OFF (default)
ON
OFF*
ON
ON
*with 2-3mA standby current
Figure 7: AAT1272 Register 1 Programming.
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:
Selecting the Boost Inductor
The AAT1272 controller utilizes PWM control and the
switching frequency is fixed. To maintain 2MHz maximum
switching frequency and stable operation, a 1ꢀH 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.
IPEAK
3
IRMS
=
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:
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 IPEAK
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
PLOSS(INDUCTOR) = I2RMS · DCR
*Denotes the default value.
w w w . a n a l o g i c t e c h . c o m
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