AAT3142ITP-T1 AnalogicTech, AAT3142ITP-T1 Datasheet - Page 12

• Manufacturer Part Number: AAT3142ITP-T1
• Description: High Efficiency 1X/1.5X/2X Charge Pump for White LED Applications
• Manufacturer: AnalogicTech

Since the AAT3142 outputs are pure constant current
sources and typically drive individual loads, it is difficult
to measure the output voltage for a given output (D1 to
D3) to derive an overall 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 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 application should be
based on trade-offs of size, external component count,
reliability, operating range, and total energy usage...not
just % efficiency.
The AAT3142 efficiency may be quantified under very
specific conditions and is dependent upon the input volt-
age versus the output voltage seen across the loads
applied to outputs D1 through D3 for a given constant
current setting. Depending upon the case of V
greater than the specific voltage seen across the loads
on D1 through D3, the device will operate in load switch
mode. If the voltage seen on the constant current source
output is less than V
1.5X or 2X charge pump mode. Each of these modes will
yield different efficiency values. Refer to the following
two sections for explanations of each operational mode.
Load Switch Mode Efficiency
The AAT3142 load switch mode is operational at all times
and functions alone to enhance device power conversion
efficiency when V
connected to the constant current source outputs. When
in load switch mode, the voltage conversion efficiency is
defined as output power divided by input power:
The expression to define the ideal efficiency (η) can be
rewritten as:
12
ChargePump
η =
IN
TM
P
is greater than voltage across the load
P
OUT
IN
IN
, then the device will operate in
=
η =
High Efficiency 1X/1.5X/2X Charge Pump for White LED Applications
V
V
OUT
IN
P
P
OUT
× I
× I
IN
OUT
OUT
=
V
V
OUT
IN
w w w . a n a l o g i c t e c h . c o m
IN
being
-or-
Charge Pump Section Efficiency
The AAT3142 contains a fractional charge pump which
will boost the input supply voltage when V
the voltage required on the constant current source out-
puts. 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 or two times the input voltage.
Efficiency (η) for an ideal 1.5X charge pump can typi-
cally 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
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
conditions from 1mA to 100mA. Efficiency will decrease
as load current drops below 0.05mA or when the level of
V
section of this datasheet for measured plots of efficiency
versus input voltage and output load current for the
given charge pump output voltage options.
IN
approaches V
η =
η(%) = 100
P
η(%) = 100
P
OUT
OUT
IN
. Refer to the Typical Characteristics
PRODUCT DATASHEET
=
V
η =
V
IN
OUT
⎛
⎝
× 1.5I
P
1.5V
⎛
⎝
V
P
× I
V
OUT
OUT
V
IN
AAT3142
OUT
OUT
IN
OUT
IN
⎞
⎠
⎞
⎠
=
1.5V
V
3142.2009.07.1.3
OUT
IN
IN
is less than