PM6644

Application information

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3

Application information

3.1

External component selection

3.1.1

Inductor selection

Once the switching frequency is defined, inductor selection depends on the desired inductor

ripple current and load transient performance.

Low inductance means greater ripple current and may generate greater output noise. On

the other hand, low inductor values involve fast load transient response.

A good compromise between the transient response time, the efficiency, the cost and the

size, is to choose the inductor value in order to maintain the inductor current ripple

occurs at the maximum input voltage. With these considerations, the inductor value can be

calculated with the following relationship:

Equation 7

In order to prevent overtemperature working conditions, the inductor must be able to provide

Equation 8

where

Equation 9

If hard saturation inductors are used, the inductor saturation current should be much greater

than the maximum inductor peak current Ipeak:

Equation 10

Using soft saturation inductors it is possible to choose inductors with a saturation current

limit at nearly Ipeak. In Table 10 there is a list of some inductor part numbers.

L

V

IN

V

OUT

–

f

sw

I

L

∆

⋅

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

V

OUT

V

IN

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

⋅

=

I

LRMS

I

()

()

2

∆I

()

()

2

12

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

+

=

∆I

()

V

INmax

V

OUT

–

f

sw

L

⋅

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

V

OUT

V

INmax

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

⋅

=

Ipeak

I

()

∆I

()

2

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

+

=