AAT2805 Datasheet, PDF (13/17 Pages) Advanced Analogic Technologies – Dual High Efficiency Charge Pump for White LED and Flash Applications

AAT2805
Dual High Efficiency Charge Pump
for White LED and Flash Applications
AS²Cwire Serial Interface Timing Diagram
EN/SET
Address
Address
T_HI
T_LO
T_LAT
1
2
17
18
0
Data
T_LAT
1
2 . . . n <= 16
1
Data Reg 1
Data Reg 2
0
n
0
Data
1
2
3
4
Max Current
20mA Max scale
30mA Max scale
15mA Max scale
Low Current Mode
Table 4: Maximum Current Settings Address 4.
Disabled Current Sinks
The backlight charge pump is equipped with an
"auto-disable" feature to protect against an LED fail-
ure condition. Current sink inputs that are not used
should be disabled. To disable and properly termi-
nate unused current sink inputs, they must be tied to
V_OUT. If left unconnected or terminated to ground, the
part will be forced to operate in 2X charge pump
mode.
Properly terminating unused current sink inputs is
important to prevent the charge pump modes from
activating prematurely. When properly terminated,
only a small sense current flows for each disabled
channel. The sense current for each disabled chan-
nel is less than 10µA.
Applications Information
LED Selection
The AAT2805 is specifically intended for driving white
LEDs. However, the device design will allow the
AAT2805 to drive most types of LEDs with forward
voltage specifications ranging from 2.0V to 4.3V.
LED applications may include main display back-
lighting, camera photo-flash applications, color
(RGB) LEDs, infrared (IR) diodes for remotes, and
other loads benefiting from a controlled output cur-
rent generated from a varying input voltage. Since
the D1 to D4 input current sinks are matched with
negligible voltage dependence, the LED brightness
will be matched regardless of the specific LED for-
ward voltage (V_F) levels.
In some instances (e.g., in high-luminous-output
applications such as photo-flash), it may be neces-
sary to drive high-V_F type LEDs. The low-dropout
current-sinks in the AAT2805 make it capable of driv-
ing LEDs with forward voltages as high as 4.3V at full
current from an input supply as low as 3.0V. Outputs
can be paralleled to drive high-current LEDs without
complication.
2805.2005.05.1.2
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