PRODUCT DATASHEET
AAT3113,AAT3114/14A
TM
ChargePump
High Efficiency 1.5X Fractional Charge Pumps For White LED Applications
tHI
tOFF
tLO
EN/SET
Code
OFF
OFF
1
2
3
Figure 2: EN/SET Timing Diagram.
T
HI > 50ns
300ns < TLO < 75µs
50ns minimum to enable
OFF
n
ON/1
2
3
4
5
6
(n < =32)
Figure 3: Enable / Disable / LED Brightness Level Set Data Input.
internal switching losses and IC quiescent current con-
LED Selection
sumption, the actual efficiency can be measured at 93%.
These figures are in close agreement for output load con-
ditions from 1mA to 100mA. Efficiency will decrease as
load current drops below 0.05mA or when the level of VIN
approaches VOUT. Refer to the Typical Characteristics sec-
tion of this datasheet for measured plots of efficiency
versus input voltage and output load current for the
given charge pump output voltage options.
AAT3113 and AAT3114/14A devices are designed to drive
white LEDs with forward voltages to 4.2V. Since the
D1:D6 output current sources are matched with negligi-
ble voltage dependence, the LED brightness will be
matched regardless of their forward voltage matching.
Charge Pump Efficiency
The AAT3113 and AAT3114/14A devices are fractional
charge pumps. The efficiency (η) can be simply defined
as a linear voltage regulator with an effective output
voltage that is equal to one and one half times the input
voltage. Efficiency (η) for an ideal 1.5X charge pump can
typically be expressed as the output power divided by
the input power:
Power Efficiency and Device Evaluation
The charge pump efficiency discussion in the previous sec-
tion only accounts for efficiency of the charge pump sec-
tion itself. Due to the unique circuit architecture and
design of the AAT3113 and AAT3114/14A, it is very diffi-
cult to measure efficiency in terms of a percent value
comparing input power over output power. Since the
device outputs are pure constant current sources, it is dif-
ficult to measure the output voltage for a given output (D1
to D6) to derive an output power measurement. For any
given application, white LED forward voltage levels can
differ, yet the output 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 quan-
tify 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 application should
be based on trade-offs of size, external components
count, reliability, operating range, and total energy
usage...not just “% efficiency.”
POUT
η =
PIN
In addition, with an ideal 1.5X charge pump, the output
current may be expressed as 2/3 of the input current.
The expression to define the ideal efficiency (η) can be
rewritten as:
POUT
PIN
VOUT · IOUT
VOUT
η =
=
=
VIN · 1.5IOUT 1.5VIN
-or-
VOUT
⎛
⎝
⎞
⎠
η(%) = 100
1.5V
IN
For a charge pump with an output of 5V and a nominal
input of 3.5V, the theoretical efficiency is 95%. Due to
w w w . a n a l o g i c t e c h . c o m
10
3113.2008.05.1.10
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