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KB3511

Kingbor Technology Co.,Ltd

TEL:(86)0755-26508846 FAX:(86)0755-26509052

APPLICATIONS INFORMATION

currents. This causes a dip in efficiency in the upper range

of low current operation. In Trickle Mode operation, lower

inductance values will cause the Trickle frequency to in-

crease.

Inductor Core Selection

Different core materials and shapes will change the size/

current and price/current relationship of an inductor.

Toroid or shielded pot cores in ferrite or permalloy mate-

rials are small and don’t radiate much energy, but gener-

ally cost more than powdered iron core inductors with

similar electrical characterisitics. The choice of which

style inductor to use often depends more on the price vs

size requirements and any radiated field/EMI require-

ments than on what the KB3511 requires to operate.

Table 1 shows some typical surface mount inductors that

work well in KB3511 applications.

In continuous mode, the input current of the converter is

series resistance (ESR) input capacitor sized for the maxi-

mum RMS current must be used. The maximum RMS

capacitor current is given by:

II

VV

V

V

RMS

MAX

OUT

IN

OUT

IN

≈

()

the peak current minus half the peak-to-peak ripple cur-

design because even significant deviations do not offer

much relief. Note that capacitor manufacturer’s ripple

current ratings are often based on only 2000 hours life-

time. This makes it advisable to further derate the capaci-

tor, or choose a capacitor rated at a higher temperature

than required. Several capacitors may also be paralleled to

meet the size or height requirements of the design. An

additional 0.1

µF to 1µF ceramic capacitor is also recom-

using an all ceramic capacitor solution.

Table 1. Representative Surface Mount Inductors

PART

VALUE

DCR

MAX DC

SIZE

NUMBER

(

µH)

(

EVERCOM

1.5

0.043

0.95

3.0

× 3.0 × 1.2

SD11

2.2

0.075

0.80

3.3

0.110

0.70

4.7

0.162

0.60

Sumida

2.2

0.116

0.950

3.5

× 4.3 × 0.8

CMD4D06

3.3

0.174

0.770

4.7

0.216

0.750

Panasonic

3.3

0.17

1.00

4.5

× 5.4 × 1.2

ELT5KT

4.7

0.20

0.95

Murata

1.0

0.060

1.00

2.5

× 3.2 × 2.0

LQH32CN

2.2

0.097

0.79

4.7

0.150

0.65

minimize voltage ripple and load step transients. Typically,

once the ESR requirement is satisfied, the capacitance is

adequate for filtering. The output ripple (

mined by:

∆≈ ∆

+

⎛

⎝⎜

⎞

⎠⎟

V

I ESR

fC

OUT

L

O

OUT

1

8

and

is highest at maximum input voltage since

with input voltage. With

with:

requirement, except for an all ceramic solution.

In surface mount applications, multiple capacitors may

have to be paralleled to meet the capacitance, ESR or RMS

current handling requirement of the application. Alumi-

num electrolytic, special polymer, ceramic and dry tantulum

capacitors are all available in surface mount packages. The

OS-CON semiconductor dielectric capacitor available from

Sanyo has the lowest ESR(size) product of any aluminum

electrolytic at a somewhat higher price. Special polymer