AAT3141
High Efficiency 1X/1.5X/2X Charge Pump
for White LED Applications
Since the AAT3141 outputs are pure constant cur-
rent sources and typically drive individual loads, it
LED Selection
The AAT3141 is specifically intended for driving
white LEDs. However, the device design will allow
the AAT3141 to drive most types of LEDs with for-
ward voltage specifications ranging from 2.0V to
4.3V. LED applications may include main and sub-
LCD display backlighting, camera photo-flash appli-
cations, color (RGB) LEDs, infrared (IR) diodes for
remotes, and other loads benefiting from a controlled
output-current generated from a varying input-volt-
age. Since the D1 to D4 output current sources are
matched with negligible voltage dependence, the
LED brightness will be matched regardless of the
specific LED forward voltage (VF) levels.
is difficult to measure the output voltage for a given
output (D1 to D4) to derive an overall output power
measurement. For any given application, white
LED forward voltage levels can differ, yet the out-
put drive current will be maintained as a constant.
This makes quantifying output power a difficult task
when taken in the context of comparing to other white
LED driver circuit topologies. A better way to quantify
total device efficiency is to observe the total input
power to the device for a given LED current drive
level. The best White LED driver for a given applica-
tion should be based on trade-offs of size, external
component count, reliability, operating range and
total energy usage...Not just "% efficiency".
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
current-sources in the AAT3141 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.
The AAT3141 efficiency may be quantified under
very specific conditions and is dependant upon the
input voltage versus the output voltage seen across
the loads applied to outputs D1 through D4 for a
given constant current setting. Depending upon the
case of VIN being greater than the specific voltage
seen across the load on D1 (or D5 when the
AAT3141 is used) the device will operate in "Load
Switch" mode. If the voltage seen on the constant
current source output is less than VIN then the
device will operate in 1.5X or 2X charge pump
mode. Each of these modes will yield different effi-
ciency values. One should refer to the following two
sections for explanations for each operational mode.
Device Switching Noise Performance
The AAT3141 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 AAT3141 soft-start feature prevents
noise transient effects associated with in-rush cur-
rents during the start up of the charge pump circuit.
Load Switch Mode Efficiency
The AAT3141 load switch mode is operational at all
times and functions alone to enhance device power
conversion efficiency when the condition exists
where VIN is greater then voltage across the load
connected to the constant current source outputs.
When in "Load Switch" mode, the voltage conver-
sion efficiency is defined as output power divided
by input power:
Power Efficiency and Device Evaluation
The charge pump efficiency discussion in the follow-
ing sections only account for the efficiency of the
charge pump section itself. Due to the unique circuit
architecture and design of the AAT3141, it is very dif-
ficult to measure efficiency in terms of a percent
value comparing input power over output power.
POUT
PIN
η =
3141.2004.07.0.91
13
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