PRODUCT DATASHEET
AAT1272
TM
SwitchReg
1.5A Step-Up Current Regulator for Flash LEDs
each code is 1dB below the previous code. The flash
safety delay can be reduced from the maximum value
programmed externally by CT in 16 linear steps. The
flash current outputs FLOUTA and FLOUTB can be
enabled or disabled individually or together. The flash-
to-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. Lastly, the EN pin must be toggled low-to-
high to enable the AAT1272 to accept I2C programming
instructions.
Applications Information
LED Selection
The AAT1272 is specifically designed to drive white flash
LEDs (typical forward voltage of 2.5V to 4.0V). Since the
FLOUTA and FLOUTB input current sinks are matched
with low voltage dependence; the LED-to-LED brightness
will be matched regardless of the individual LED forward
voltage (VF) levels.
Flash Mode LED Current
Over-Temperature Protection
The LED current is controlled by the RSET resistor. For
maximum accuracy, a 1% tolerance resistor is recom-
mended. FLOUTA and FLOUTB can be programmed up to
a maximum total flash current of 1.5A or up to 750mA
per channel. FLOUTA and FLOUTB output current is
matched across the programming range. A flash event is
initiated by asserting the FLEN pin. A flash event is auto-
matically terminated when FLEN is disabled or if the
safety timer terminates before the FLEN pin is disabled.
Thermal protection disables the AAT1272 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 maximum flash current in each FLOUTA and FLOUTB
is set by the RSET resistor and can be calculated using the
following equation:
The AAT1272’s output voltage is limited by internal over-
voltage protection circuitry, which prevents damage to
the AAT1272 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.
81kꢀ · A 81kꢀ · A
IFLOUTA = IFLOUTB
=
=
= ~750mA per channel
RSET
107kꢀ
To prevent excessive power dissipation during higher
flash current operation, RSET values smaller than 107kΩ
are not recommended.
Movie Mode LED Current
Auto-Disable Feature
The maximum movie-mode current level is set by the
maximum, programmed flash current reduced by the
programmed flash-to-movie-mode ratio in which the
default value is 7.3:
The AAT1272 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.
IFLOUT[A/B](MAX)
750mA
7.3
IMOVIE-MODE[A/B]
=
=
= 103mA
7.3
To change the configuration or the settings, the AAT1272
can be programmed via the I2C interface. Triggering the
FLEN low to high will enable a flash event with the max-
imum flash current set by the RSET resistor or with pro-
grammed flash current set via the I2C interface.
Concurrently, the flash timer is also initiated. All data
and register contents are cleared (reset to the default
value) after each flash event.
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1272.2009.04.1.2
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