AAT3113 データシートの表示（PDF） - Analog Technology Inc

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AAT3113

High Efficiency 1.5X Fractional Charge Pumps For White LED Applications

Analog Technology Inc 

PRODUCT DATASHEET

AAT3113, AAT3114/14A

ChargePumpTM High Efficiency 1.5X Fractional Charge Pumps For White LED Applications

EN/SET

Code OFF

tHI

tLO

tOFF

1

2

3

OFF

Figure 2: EN/SET Timing Diagram.

THI > 50ns

300ns < TLO < 75µs

50ns minimum to enable

ON/1

2

3

4

5

6

n

(n < =32)

OFF

Figure 3: Enable / Disable / LED Brightness Level Set Data Input.

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:

η

=

POUT

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:

-or-

η = POUT = VOUT · IOUT = VOUT

PIN VIN · 1.5IOUT 1.5VIN

η(%)

=

100

⎛

⎝

VOUT ⎞

1.5VIN⎠

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 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.

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.”

10

www.analogictech.com

3113.2008.05.1.10

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