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BD9152MUV

Technical Note

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Selection of components externally connected

1. Selection of inductor (L)

※

Current exceeding the current rating of the inductor results in magnetic saturation of the inductor, which decreases efficiency.

The inductor must be selected allowing sufficient margin with which the peak current may not exceed its current rating.

※

Select the inductor of low resistance component (such as DCR and ACR) to minimize dissipation in the inductor for better

efficiency.

The inductance significantly depends on output ripple current.

As seen in the equation (1), the ripple current decreases as the

inductor and/or switching frequency increases.

Δ

[A]・・・(1)

Appropriate ripple current at output should be 20% more or less of the

maximum output current.

Δ

L=

Δ

[H]・・・(3)

Output capacitor should be selected with the consideration on the stability region

and the equivalent series resistance required to smooth ripple voltage.

Output ripple voltage is determined by the equation (4)：

Δ

※

Rating of the capacitor should be determined allowing sufficient margin against

output voltage. A 22μF to 100μF ceramic capacitor is recommended.

Less ESR allows reduction in output ripple voltage.

Fig.34 Output capacitor

(5-1.2)×1.2

0.45×5×1.0M

L=

=2.02μ → 2.2[μH]

Δ

Fig.33 Output ripple current

IL

L

Co

L

Co

ESR