AN2713 datasheet(14/40 Pages) STMICROELECTRONICS

14 / 40 page

Component selection guidelines

AN2713

14/40

Doc ID 14431 Rev 1

In this condition the switch peak current is calculated using the formula in Equation 2.

Equation 2

where

●

Eff is the efficiency of the DC-DC converter (93% typ. at highest load)

●

L is the inductance (22 µH typ.)

●

F is the PWM frequency (220 kHz typ.).

Example:

Application conditions:

●

Voutmax= 19.2 V (supposing EN=VSEL=1, LLC=0)

●

Vinmin= 11 V

●

Vupmax=Voutmax+Vdrop= 19.2 V+0.75 V= 19.95 V

●

Ioutmax= 500 mA

●

Eff=90%

Based on Equation 2 and the preceding application conditions, IPEAK is:

Equation 3

Several inductors suitable for the LNBH23 are listed in theTable 4, although there are many

other manufacturers and devices that can be used. Consult each manufacturer for more

detailed information and for their entire selection of related parts, since many different

shapes and sizes are available. Ferrite core inductors should be used to obtain the best

efficiency. Choose an inductor that can handle at least the IPEAK current without saturating,

and ensure that the inductor has a low DCR (copper wire resistance) to minimize power

losses and, consequently, to maximize total efficiency.

Table 4.

Recommended inductors

Vendor

Part number

Isat(A)

DRC (m

Ω)

Mounting type

Sumida

CD104-220MC

RHC110-220M

1.6

2.4

SMD

Through-hole

Toko

822LY-220K

824LY-220K

A671HN-220L

A814LY-220M

1.3

1.72

2.44

2.0

Through-hole

SMD

Ipeak

VUP

max

Iout

max

⋅

Eff Vin

min

⋅

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

Vin

min

2LF

----------------- 1

Vin

min

VUP

max

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

–

⎝⎠

⎛⎞

Ipeak

19.95 0.5

⋅

0.9 11

⋅

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

22210

–

220 10

⋅⋅

⋅

----------------------------------------------------------- 1

19.95

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

–

⎝⎠

⎛⎞

1.52 A

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