AAT3153 Datasheet, PDF (10/14 Pages) Advanced Analogic Technologies – High Efficiency 1X/1.5X/2X Charge Pump For White LED Applications

AAT3153
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
S²Cwire Serial Interface Timing
EN/SET
Data Reg
T _HI
T _LO
T_LAT
1
2
n n <= 16
1
T_OFF
n
0
Auto-Disable Feature
The AAT3153 is equipped with an auto-disable fea-
ture for each LED channel. After the IC is enabled
and started up, a test current of 150µA (typical) is
forced through each sink channel. The channel will
be disabled if the voltage of that particular SINK pin
does not drop to certain threshold. This feature is
very convenient for disabling an unused channel or
during an LED fail short event.
Thermal Protection
The AAT3153 has a built-in thermal protection cir-
cuit that will shut down the charge pump if the die
temperature rises above the thermal limit, as is the
case during a short-circuit of the V_OUT pin.
Applications Information
LED Selection
Although the AAT3153 is specifically intended for
driving white LEDs, the device can also be used to
drive most types of LEDs with forward voltage
specifications ranging from 2.0V to 4.7V. LED
applications may include main and sub-LCD dis-
play backlighting, camera photo-flash applications,
color (RGB) LEDs, infrared (IR) diodes for remotes,
and other loads benefiting from a controlled output
current generated from a varying input voltage.
Since the D1 to D6 input current sinks are matched
with negligible voltage dependence, the LED
brightness will be matched regardless of the spe-
cific LED forward voltage (V_F) levels. In some
instances (e.g., in high luminous output applica-
10
tions such as photo flash), it may be necessary to
drive high-V_F type LEDs. The low-dropout current
sinks in the AAT3153 make it capable of driving
LEDs with forward voltages as high as 4.7V at full
current from an input supply as low as 3.0V.
Outputs can be paralleled to drive high-current
LEDs without complication.
Device Switching Noise Performance
The AAT3153 operates at a fixed frequency of
approximately 1MHz to control noise and limit har-
monics that can interfere with the RF operation of
cellular telephone handsets or other communica-
tion devices. Back-injected noise appearing on the
input pin of the charge pump is 20mV peak-to-
peak, typically ten times less than inductor-based
DC/DC boost converter white LED backlight solu-
tions. The AAT3153 soft-start feature prevents
noise transient effects associated with inrush cur-
rents during start-up of the charge pump circuit.
Power Efficiency and Device Evaluation
The charge pump efficiency discussion in the follow-
ing sections only accounts for the efficiency of the
charge pump section itself. Due to the unique circuit
architecture and design of the AAT3153, it is very dif-
ficult to measure efficiency in terms of a percent
value comparing input power over output power.
Since the AAT3153 inputs are pure constant current
sinks and typically drive individual loads, it is difficult
to measure the output voltage for a given input (D1
to D6) to derive an overall output power measure-
ment. For any given application, white LED forward
voltage levels can differ, yet the load drive current
will be maintained as a constant.
3153.2005.12.0.93