AL1672 datasheet(10/14 Pages) DIODES

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AL1672

Document number: DS39344 Rev. 1 - 2

10 of 14

www.diodes.com

July 2017

AL1672

Functional Description and Application Information (Cont.)

Operation Parameters Design

Setting the Current Sense Resistor RCS

The current sense resistance can be calculated as following:

REF

O MEAN





------------------------------------------------ (8)

Where IO_MEAN is the mean output current; RCS is current sense resister which is shown as figure1;

VREF is internal reference voltage that is equal to 0.3V;

Buck Inductance Selection (L2)

The switching frequency is not constant for the AL1672 due to boundary conduction mode. To set the minimum switching frequency fMIN at the

crest of the minimum AC input, primary inductance can be obtained by below formula.

( 2

sin( )

)

MIN

O MEAN

MIN

V dt



















------------------------------------------------ (9)

Where VIN_MIN is the minimum input AC voltage; IO_MEAN is the mean output current; VO is the output voltage; fMIN is the minimum switching

frequency at the crest of the minimum AC input;

For boundary conduction mode and constant on time method, the peak current of primary inductance can be calculated as below.

( 2

)

IN MIN

MIN











------------------------------------------------ (10)

Where VIN_MIN is the minimum input AC voltage; IP is the max peak current of inductance. VO is the output voltage; fMIN is the minimum switching

frequency at the crest of the minimum AC input.

According to the Faraday’s Law, the winding number of the inductance can be calculated by:







------------------------------------------------ (11)

Where Ae is the core effective area. Bm is the maximum magnetic flux density.

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