1.5A Step-Up Current Regulator for Flash LEDs
Flash/Safety Timer – Address 1
A timer function that enables the flash current sinks for
a programmed amount of time is incorporated in the
AAT1290. The on-time is programmed by loading the
Timing Register at Address 1 with a value from 1 to 16
and by choosing a value for the external timing capaci-
tor, CT (see Table 3). When data is latched into Address
1, the data will be used at the next occurrence of an
asserted FLEN, it will then revert to the default value of
Data 1, or 16/16. This feature eliminates the need for an
external, housekeeping baseband controller to contain a
safety delay routine. The flash safety timer also serves
as a protection feature to minimize thermal issues with
the flash LEDs in the event the external controller’s flash
routine experiences a software failure. If no write
instruction is applied to Address 1, then the safety timer
will default to the maximum delay programmed exter-
nally by CT.
The Flash Time T can be calculated by the following
Where T is in seconds and CT is in µF.
For example, using a 47nF capacitor at CT sets the flash
Flash Timeout =
× 68nF = 600ms
The relationship between the flash safety timeout and
the capacitance of the timer capacitor is illustrated in
(IFL = 1.5A; VIN
0 20 40 60 80 100 120 140
CT Capacitor (nF)
Figure 2: Flash Safety Timeout
vs. Timer Capacitor.
1 A small current will flow due to the start-up test current.
* Default value.
Ratio of MM Timeout
Table 3: Address 1, Flash Safety Timer
Programming; Maximum Value
Programmed by CT.
Movie Mode Enable – Address 2
To enable or disable the flash, a write instruction to
Address 2 is applied to the AAT1290’s EN/SET pin. If no
write instruction is applied, the default value for Address
2 is OFF. During a flash event, the LED will be enabled
regardless of the movie-mode setting.
Movie Mode Enable
Table 4: Address 2, Movie Mode
Skyworks Solutions, Inc. • Phone  376-3000 • Fax  376-3100 • firstname.lastname@example.org • www.skyworksinc.com
202106A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 26, 2012