AN4501 datasheet(21/48 Pages) STMICROELECTRONICS

21 / 48 page

DocID026394 Rev 1

21/48

AN4501

Selection of the inductor

Equation 10:

Using the expression of IL,PP from Equation 5 gives:

Equation 11:

As we will see, in most of the cases, the variation of IL,PEAK with the duty cycle is dictated by

the term IOUT/(1 - D) if the IL,PP is lower than IL. Therefore, in general IL,PEAK MAX is reached

at the DMAX (and VINMIN). This property can be verified by calculating the derived function of

IL,PEAK:

Equation 12:

In general the ratio between the inductor current peak-to-peak current and the inductor

average current is kept below 1. Therefore:

Equation 13:

Therefore:

Under these conditions,

therefore the peak current is a monotonically

increasing function which reaches its maximum at DMAX (and VIN,MIN):

Equation 14:

L,PEAK

LPP

--------------

L,PEAK

OUT

–

-------------

OUT

–

()

×η

---------------------------------------------------

L,PEAK

-----------------------

OU T

–

()

---------------------

OUT

12D

–

()

×η

--------------------------------------------

OU T

–

()

×η

---------------------------------------------------

OU T

–

-------------

≤

OUT

×η

--------------------------------

OUT

–

()

---------------------

≤

L,PEAK

-----------------------

OU T

–

()

---------------------

OU T

×η

--------------------------------

–

OUT

×η

-----------------------------------------

OU T

2LF

×η

-----------------------------------------

≥

L,PEAK

-----------------------

L,PEAK,MAX

OU T

MAX

–

-------------------------

OU T

MAX

–

()

×η

---------------------------------------------------------------------------

AN4501 Scheda tecnica(PDF) 21 Page - STMicroelectronics

AN4501 Scheda tecnica(HTML) 21 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Scheda tecnica Scarica

Link URL