AAT1271 Datasheet, PDF (10/19 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
disabled individually or together. Lastly, the flash to
maximum movie mode current ratio can be set from 1:2
to 1:30 with respect to the maximum programmed flash
current. The FLEN signal takes priority over movie-mode
operation.
Movie mode operation is controlled entirely by the
AS²Cwire interface via the EN/SET pin. Address 2 con-
trols the movie mode on and off functions. Using this
register either or both of the LED channels can be turned
on to the current values set in Address registers 0 and
3. The movie mode is not operational when the FLEN pin
is high and the part is in flash mode operation. If the
AAT1271 is in movie mode (FLEN=low) and the FLEN is
strobed high the movie mode state will end and the part
will operate in the flash mode. The part will not reenter
movie mode when ENFL is brought low. To reenter movie
mode after a flash event the part must be turned off and
the AS²Cwire interface must be reprogrammed to the
desired movie mode level.
Over-Temperature Protection
Thermal protection disables the AAT1271 when internal
power dissipation becomes excessive, as it disables both
MOSFETs. The junction over-temperature threshold is
140°C with 15°C of temperature hysteresis. The output
voltage automatically recovers when the over-tempera-
ture fault condition is removed.
Over-Voltage Protection
(Open LED, Open Circuit)
The AAT1271’s output voltage is limited by internal over-
voltage protection circuitry, which prevents damage to
the AAT1271 from open LED or open circuit conditions.
During an open circuit, the output voltage rises and
reaches 5.5V (typical), and the OVP circuit disables the
switching, preventing the output voltage from rising
higher. Once the open circuit condition is removed,
switching will resume. The controller will return to nor-
mal operation and maintain an average output voltage.
Auto-Disable Feature
The AAT1271 is equipped with an auto-disable feature
for each LED channel. After the IC is enabled and started
up, a test current of 2-3mA (typical) is forced through
each sink channel. The channel will be disabled if the
voltage of that particular SINK pin does not drop to a
certain threshold. This feature is very convenient for
disabling an unused channel or during an LED fail-short
event. This small test current should be added to the set
output current in both Flash and MM conditions.
Timing Diagram
FLASH
FLASH
FLASH
FLASH
MOVIE MODE
LED CURRENT
EN/SET
DATA TO
MOVIE-MODE
LEVEL
NO FLASH
FLASH LOWERED
TO DEFAULT
MOVIE-MODE
DURING FLINH
NO FLASH
FLASH
tDLY(CT)
FLASH TIMES OUT
FLASH TIMES OUT
SET BY CT
tDLY(CT)
FLASH ENABLE
FLASH INHIBIT
No AS²C address programming shown.
10
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1271.2008.08.1.1