AAT1271 Datasheet, PDF (12/19 Pages) Advanced Analogic Technologies – 1.5A Step-Up Current Regulator for Flash LEDs

SwitchReg^TM
PRODUCT DATASHEET
AAT1271
1.5A Step-Up Current Regulator for Flash LEDs
When EN/SET is strobed low and held low longer than
t_OFF (500μs), the AAT1271 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 AAT1271’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 AAT1271 movie mode current settings are controlled
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 cur-
rent is set by Address register 3 (discussed below). The
default ratio between the flash current level and maxi-
mum movie mode current level is 1:7.3. The corre-
sponding 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^TM Serial Interface Timing.
* Denotes the default value.
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1271.2008.08.1.1