PRODUCT DATASHEET
AAT1272
TM
SwitchReg
1.5A Step-Up Current Regulator for Flash LEDs
Functional Block Diagram
IN
SW
OUT
FLOUTA
FLOUTB
EN
FLEN
SCL
Control
SDA
RSET
CT AGND PGND FLGND
I2C-compliant interface allows further adjustment of the
Functional Description
flash timer duration. This allows the flash timer duration
to be reduced in 16 linear steps from the maximum time
set by the timing capacitor. If the safety timer is not
needed in the application, it can be disabled by connect-
ing the CT pin directly to AGND.
The AAT1272 is a boost converter with a current-regulat-
ed output designed to drive high current white LEDs
used in camera flash applications. The maximum flash
current is set by an external resistor, RSET, which sets the
flash current and the maximum movie-mode current.
The maximum movie-mode current is equal to the max-
imum programmed flash current minus the programmed
flash-to-movie-mode ratio whose default value is 7.3.
The AAT1272 has two LED current sources which share
the output current equally. For a single white LED appli-
cation, the two current sources can be connected togeth-
er to apply full output current into the LED. In two LED
applications, each diode can be connected to its corre-
sponding current source (FLOUTA or FLOUTB) and the
output current will be shared. In applications where only
one LED is connected to either FLOUTA or FLOUTB, the
unused current sink must be directly connected to OUT,
thereby disabling that channel.
A flash pulse is initiated by strobing the FLEN input pin
low-to-high, which initiates a flash pulse and also starts
the internal timer. The maximum flash current in the
AAT1272 is set by an external resistor, RSET, which sets
the flash current and the maximum movie-mode current
reduced by a factor of 2. The flash timer will terminate
the flash current regardless of the status of the FLEN pin.
This can be either used as a simple flash timing pulse or
can be used as a safety timer in the event of a control
logic malfunction to prevent the LED from over-heating.
Movie Mode
The movie mode current level, the flash safety timer,
the output channel enable, and the flash-to-movie mode
current ratio can be set using the AAT1272’s I2C-
compliant interface. The movie-mode current level can
be adjusted in 16 steps using a logarithmic scale where
The maximum flash time is determined by an external
timing capacitor connected to the CT pin. The flash dura-
tion can be set from 50ms up to a maximum of 1s. The
w w w . a n a l o g i c t e c h . c o m
10
1272.2009.04.1.2
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
