AAT1271A Datasheet, PDF (12/19 Pages) Advanced Analogic Technologies – 1.5A Step-Up Current Regulator for Flash LEDs

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PROPRIETARY INFORMATION PRODUCT DATASHEET
AAT1271A
1.5A Step-Up Current Regulator for Flash LEDs
When EN/SET is strobed low and held low longer than
t_OFF (500μs), the AAT1271A enters shutdown mode and
draws less than 1uA from V_IN. All data and address are
cleared (reset to 0) during shutdown.
The AS²Cwire addressing allows the control of the movie-
mode output current, the safety timer delay, indepen-
dent control of the FLOUTA and FLOUTB current sinks,
and the ratio of movie-mode current to flash current.
If there are no programmed write instructions applied to
the EN/SET pin prior to the assertion of the FLEN pin and
the device is enabled, then all registers will be loaded
with their default values shown in Table 1. In the event
that the number of rising edges applied at the EN/SET
pin is less than 17, the AAT1271A’s state machine will
interpret instruction to program the output currents to
the desired current level for movie-mode operation.
Movie Mode Current – Address 0
The AAT1271A movie mode current settings are con-
trolled using the AS²Cwire interface. Movie Mode current
has a maximum value of 50% of the flash current with
240 possible current levels. The maximum movie mode
current is set by Address register 3 (discussed below).
The default ratio between the flash current level and
maximum movie mode current level is 1:7.3. The cor-
responding FLOUTA/FLOUTB maximum movie mode cur-
rent can be calculated:
I_{MOVIE MODE[A/B]}
=
I_{FLOUT[A/B]MAX}
7.3
For example, if an R_SET value of 107kΩ is chosen, then
the FLOUTA/FLOUTB flash current is set to 750mA. For
movie mode operation, the maximum current available
at either FLOUTA or FLOUTB is then:
I = _{MOVIE MODE[A/B]}
I_{FLOUT[A/B]MAX}
7.3
=
750mA
7.3
=
103mA
Address 0 controls precise movie mode current levels.
The FLOUTA/FLOUTB movie-mode current can be adjust-
ed in logarithmic fashion to one of 16 steps represented
as a fraction of the maximum movie mode current in
Table 2. To adjust the movie-mode current the user must
first access Address 0 before writing the data to set the
MM Current value.
Data
1*
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Percentage of Maximum MM Current
100%
89%
79%
71%
63%
56%
50%
45%
40%
36%
32%
28%
25%
22%
20%
0%
Table 2: Address 0, Movie Mode
Current Programming.
EN/SET
Address
Address
T _HI
T _LO
T_LAT
1
2
16
17
0
Data
T_LAT
1
2 . . . n ≤ 16
1
Data Reg 1
0
n
Figure 1: AS²Cwire Serial Interface Timing.
*Denotes the default value.
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1271A.2008.07.1.0