AAT2848 Datasheet, PDF (12/19 Pages) Advanced Analogic Technologies – High-Current Charge Pump For Backlight Display and Flash Applications

ChargePump^TM
PRODUCT DATASHEET
AAT2848
High-Current Charge Pump For Backlight Display and Flash Applications
BENS/FENS
Data Reg
t _HI
t _LO
t _LAT
1
2
n-1 n 32/16
0
t _OFF
n-1
0
Figure 3: S²Cwire Serial Interface Timing.
The flash LED current is programmed by the R_FSET resis-
tor with the following equation:
2880
R_FSET = _IFLED
R_FSET = Flash LED Current Programming Resistor
I_FLED = Flash LED Current
Backlight Fade-In/
Fade-Out Functionality
The AAT2848 contains internal circuitry that automates
fade-in/fade-out operation. Fade functionality simply
allows for the turning off/on of the LEDs in a smooth
controlled transition. The AAT2848 does not have to be
manually programmed to avoid the abrupt changes in
lighting when white LED drivers are shutdown/turned-off.
The fade-in/fade-out operation occurs only during device
on/off transitions. The response time is constant regard-
less of the LED current level.
The backlight fade-in/fade-out response time (t_FADE) can
be calculated using the following equation:
t_FADE = 57 s/μF · C_FADE
where t_FADE is in seconds and C_FADE is in μF. For example,
for a 0.047μF capacitor:
t_FADE = 57 s/μF · 0.047μF = 2.7s
To disable the fade-in/fade-out timer, connect the FADE
pin to IN.
Auto Disable Feature
The charge pump in AAT2848 is equipped with an auto-
disable feature for each LED channel. After the IC is
enabled and started up, a test current of 1.5mA (typical)
is forced through each sink channel. The channel will be
disabled if the voltage of that particular BLX or FLX pin
does not drop to a certain threshold. This feature is con-
venient for disabling an unused channel or during a
flash/backlight LED failed short event.
Thermal Protection
The charge pump has a built-in thermal protection cir-
cuit that will shut down the charge pump if the die tem-
perature rises above the thermal limit as is the case
during a short circuit of the OUT pin.
12
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2848.2008.05.1.0