AAT1270_08 Datasheet, PDF (11/18 Pages) Advanced Analogic Technologies – 1A Step-Up Current Regulator for Flash LEDs

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PRODUCT DATASHEET
AAT1270
1A Step-Up Current Regulator for Flash LEDs
Alternatively, the AAT1270 S²Cwire interface programs
the movie mode current at a reduced level. The FLOUTA/
FLOUTB movie-mode current can be adjusted in loga-
rithmic fashion to one of 16 steps. Table 1 illustrates
approximate movie mode levels to which the AAT1270
movie mode operation can be programmed.
S²Cwire Data
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Percentage of Maximum
Movie Mode Current (%)
100
89
79
71
63
56
50
44.7
39.8
35.5
31.6
28.2
25.1
22.4
20
0
Table 1: Programming Movie Mode
Current via S²Cwire (%).
S²Cwire Serial Interface
The Simple Serial Control (S²Cwire) serial interface
records rising edges at the EN/SET pin and decodes
them into 16 different states. The S²Cwire serial inter-
face has flexible timing. Data can be applied at speeds
faster than 1MHz, or at much slower speeds, such as
15kHz. After data is applied, EN/SET is strobed high and
held high to latch the data.
Once the signal applied at the EN/SET pin has been held
in the logic high state for time longer than t_LAT (500μs),
the programmed current becomes active and the internal
data register is reset to zero. For subsequent current level
programming, the number of rising edges corresponding
to the desired code must be applied to the EN/SET pin.
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 external, house-
keeping baseband controller to contain a safety delay
routine. It also serves as a protection feature to mini-
mize thermal issues with the flash LEDs in the event an
external controller’s flash software routine experiences
hang-up or freeze.
The flash timeout T can be calculated by the following
equation:
T = 21.5s/µF · C_T
Where T is in seconds and C_T is the capacitance of the
timer capacitor in μF.
For example, using a 47nF capacitor for C_T sets the flash
timeout to:
Flash Timeout = 21.5s/µF · 0.047µF = 1s
EN/SET
Data Reg
T_HI
T_LO
T _LAT
1
2
n-1
n ≤ 16
0
TOFF
n-1
0
Figure 1: S²Cwire Serial Interface Timing.
1270.2008.07.1.5
www.analogictech.com
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