AAT3142 datasheet(13/16 Pages) AAT

13 / 16 page

AAT3142

High Efficiency 1X/1.5X/2X Charge Pump

for White LED Applications

3142.2007.03.1.2

devices. Back-injected noise appearing on the input

pin of the charge pump is 20mV peak-to-peak, typi-

cally ten times less than inductor-based DC/DC

boost converter white LED backlight solutions. The

AAT3142 soft-start feature prevents noise transient

effects associated with inrush currents 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 efficiency of the

charge pump section itself. Due to the unique circuit

architecture and design of the AAT3142, it is very dif-

ficult to measure efficiency in terms of a percent

value comparing input power over output power.

Since the AAT3142 outputs are pure constant cur-

rent 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 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.

The AAT3142 efficiency may be quantified under

very specific conditions and is dependent upon the

input voltage 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

IN being 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

IN, then the device will operate in 1.5X or 2X charge

pump mode. Each of these modes will yield differ-

ent efficiency values. Refer to the following two sec-

tions 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

IN is greater than volt-

age across the load connected to the constant cur-

rent source outputs. When in load switch mode,

the voltage conversion efficiency is defined as out-

put power divided by input power:

The expression to define the ideal efficiency (

η)

can be rewritten as:

-or-

Charge Pump Section Efficiency

The AAT3142 contains a fractional charge pump

which will boost the input supply voltage when V

is less than the voltage required on the constant

current source outputs. 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 typically be

expressed as the output power divided by the input

power:

η =

OUT

η(%) = 100

OUT

⎛⎞

⎝⎠

η =

OUT =

OUT

× I

OUT =

OUT

× I

OUT

η =

OUT

AAT3142 Datasheet(PDF) 13 Page - Advanced Analog Technology, Inc.

AAT3142 Datasheet(HTML) 13 Page - Advanced Analog Technology, Inc.

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Datasheet Download

Link URL