AAT2805
Dual High Efficiency Charge Pump
for White LED and Flash Applications
AS2Cwire Serial Interface Timing Diagram
Address
THI
Data
TLAT
TLO
TLAT
EN/SET
1
2
17
18
1
2 . . .
n <= 16
Address
Data Reg 1
Data Reg 2
0
1
0
0
n
Applications Information
Data
Max Current
1
2
3
4
20mA Max Scale
30mA Max Scale
15mA Max Scale
Low Current Mode
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 (VF) levels.
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 failure con-
dition. Current sink inputs that are not used should
be disabled. To disable and properly terminate
unused current sink inputs, they must be tied to VOUT
.
If left unconnected or terminated to ground, the part
will be forced to operate in 2X charge pump mode.
In some instances (e.g., in high-luminous-output
applications such as photo flash), it may be neces-
sary to drive high-VF type LEDs. The low dropout cur-
rent sinks in the AAT2805 make it capable of driving
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.
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 120µA.
2805.2006.04.1.7
13
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
