AAT2806 datasheet(14/16 Pages) AAT

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AAT2806

Dual High Efficiency Charge Pump

for White LED and Flash Applications

2806.2006.04.1.8

The expression to define the ideal efficiency (

η) can

be rewritten as:

-or-

Charge Pump Mode Efficiency: Fractional charge

pumps will boost the input supply voltage in the event

where VIN is less than the voltage required on the con-

stant 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 a 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:

In addition, with an ideal 1.5X charge pump, the out-

put current may be expressed as 2/3 of the input cur-

rent. The expression to define the ideal efficiency (

η)

can be rewritten as:

-or-

For a charge pump with an output of 5V and a nom-

inal input of 3.5V, the theoretical efficiency is 95%.

Due to internal switching losses and IC quiescent

current consumption, the actual efficiency can be

measured at 93%. These figures are in close agree-

ment for output load conditions from 1mA to 100mA.

Efficiency will decrease as load current drops below

0.05mA or when the level of VIN approaches VOUT.

Flash Charge Pump: The flash charge pump is a

regulated output voltage doubling charge pump. The

efficiency is defined as a linear voltage regulator with

an effective output voltage that is equal to two times

the input voltage. The expression to define the ideal

efficiency can be written as:

-or-

For a charge pump with an output of 5V and a nom-

inal input of 3V, the theoretical efficiency is 83.3%.

Due to internal switching losses and IC quiescent

current consumption, the actual efficiency can be

measured at approximately 82%. Efficiency will

decrease as the level of VIN approaches that of the

regulated VOUT. Refer to the device typical charac-

teristics curves for expected actual efficiency

based on either input voltage or load current.

η(%) = 100

VOUT

2.0VIN

⎛⎞

⎝⎠

η = POUT = VOUT × IOUT = VOUT

VIN × 2.0IOUT

2.0VIN

η(%) = 100

VOUT

1.5VIN

⎛⎞

⎝⎠

η = POUT = VOUT × IOUT = VOUT

VIN × 1.5IOUT

1.5VIN

η =

POUT

η(%) = 100

VOUT

VIN

⎛⎞

⎝⎠

η = POUT = VOUT × IOUT = VOUT

VIN × IOUT

VIN

AAT2806 Datasheet(PDF) 14 Page - Advanced Analog Technology, Inc.

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