AAT2848 Analogic Corporation, AAT2848 Datasheet - Page 12

• Manufacturer Part Number: AAT2848
• Manufacturer: Analogic Corporation

The flash LED current is programmed by the R
tor with the following equation:
R
I
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
be calculated using the following equation:
where t
for a 0.047μF capacitor:
12
ChargePump
FLED
FSET
= Flash LED Current
= Flash LED Current Programming Resistor
FADE
is in seconds and C
t
FADE
= 57 s/μF · 0.047μF = 2.7s
t
TM
FADE
BENS/FENS
R
= 57 s/μF · C
Data Reg
FSET
High-Current Charge Pump For Backlight Display and Flash Applications
=
2880
I
FADE
FLED
is in μF. For example,
FADE
Figure 3: S
1
2
w w w . a n a l o g i c t e c h . c o m
FSET
FADE
2
t
Cwire Serial Interface Timing.
LO
n-1
0
resis-
) can
t
HI
n 32/16
t
LAT
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.
n-1
PRODUCT DATASHEET
t
OFF
AAT2848
0
2848.2008.05.1.0