AAT3113ITP ANALOGICTECH [Advanced Analogic Technologies], AAT3113ITP Datasheet - Page 10

• Manufacturer Part Number: AAT3113ITP
• Description: High Efficiency 1.5X Fractional Charge Pumps For White LED Applications
• Manufacturer: ANALOGICTECH [Advanced Analogic Technologies]

LED Selection
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:
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:
-or-
For a charge pump with an output of 5V and a nominal
input of 3.5V, the theoretical efficiency is 95%. Due to
10
ChargePump
ON/1
η =
P
P
OUT
η(%) = 100
IN
TM
T
2
HI
=
Figure 3: Enable / Disable / LED Brightness Level Set Data Input.
> 50ns
V
High Efficiency 1.5X Fractional Charge Pumps For White LED Applications
η =
V
IN
OUT
· 1.5I
3
P
P
· I
OUT
⎛
⎝
IN
1.5V
OUT
V
EN/SET
OUT
Code
OUT
IN
4
=
⎞
⎠
1.5V
V
Figure 2: EN/SET Timing Diagram.
OUT
OFF
IN
5
w w w . a n a l o g i c t e c h . c o m
6
1
300ns < T
AAT3113, AAT3114/14A
t
LO
t
HI
internal switching losses and IC quiescent current con-
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 V
approaches V
tion of this datasheet for measured plots of efficiency
versus input voltage and output load current for the
given charge pump output voltage options.
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.”
LO
2
< 75µs
3
OUT
t
. Refer to the Typical Characteristics sec-
OFF
(n < =32)
OFF
n
PRODUCT DATASHEET
50ns minimum to enable
OFF
3113.2008.05.1.10
IN