PRODUCT DATASHEET
AAT2848
TM
ChargePump
High-Current Charge Pump For Backlight Display and Flash Applications
tHI
tOFF
tLO
tLAT
BENS/FENS
Data Reg
1
2
n-1
n 32/16
0
n-1
0
Figure 3: S2Cwire Serial Interface Timing.
The flash LED current is programmed by the RFSET resis-
tor with the following equation:
To disable the fade-in/fade-out timer, connect the FADE
pin to IN.
2880
IFLED
Auto Disable Feature
RFSET
=
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.
RFSET = Flash LED Current Programming Resistor
IFLED = 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.
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.
The backlight fade-in/fade-out response time (tFADE) can
be calculated using the following equation:
tFADE = 57 s/μF · CFADE
where tFADE is in seconds and CFADE is in μF. For example,
for a 0.047μF capacitor:
tFADE = 57 s/μF · 0.047μF = 2.7s
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2848.2008.05.1.0
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