BD8963EFJ(2010) Ver la hoja de datos (PDF) - ROHM Semiconductor

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componentes Descripción

Fabricante

BD8963EFJ
(Rev.:2010)

Low Noise High-efficiency Switching Regulator with Built-in Power MOSFET

ROHM Semiconductor 

BD8963EFJ

●Selection of components externally connected

1. Selection of inductor (L)

IL

ΔIL

VCC

IL

VOUT

L

Co

Fig.25 Output ripple current

Technical Note

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.

(VCC-VOUT)×VOUT

ΔIL=

L×VCC×f

[A]・・・(1)

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

maximum output current.

ΔIL=0.2×IOUTmax. [A]・・・(2)

(VCC-VOUT)×VOUT

L=

ΔIL×VCC×f

[H]・・・(3)

(ΔIL: Output ripple current, and f: Switching frequency)

*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.

If VCC=5V, VOUT=1.1V, f=1MHz, ΔIL=0.2×3A=0.6A, for example,(BD8963EFJ)

(5-1.1)×1.1

L= 0.6×5×1M =1.43µ → 1.5[µH]

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

efficiency.

2. Selection of output capacitor (CO)

VCC

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)：

VOUT

L

ESR

Co

Fig.26 Output capacitor

ΔVOUT=ΔIL×ESR [V]・・・(4)

(ΔIL: Output ripple current, ESR: Equivalent series resistance of output capacitor)

*Rating of the capacitor should be determined allowing sufficient margin against

output voltage. A 10μF to 100μF ceramic capacitor is recommended.

Less ESR allows reduction in output ripple voltage.

3. Selection of input capacitor (Cin)

VCC

Cin

Input capacitor to select must be a low ESR capacitor of the capacitance

sufficient to cope with high ripple current to prevent high transient voltage. The

ripple current IRMS is given by the equation (5):

VOUT

L

Co

Fig.27 Input capacitor

√VOUT(VCC-VOUT)

IRMS=IOUT×

VCC

[A]・・・(5)

< Worst case > IRMS(max.)

When Vcc is twice the VOUT, IRMS=

IOUT

2

If VCC=5V, VOUT=1.1V, and IOUTmax.= 3A, (BD8963EFJ)

IRMS=3×

√1.1×(5-1.1)

5

=1.24[ARMS]

A low ESR 10µF/10V ceramic capacitor is recommended to reduce ESR dissipation of input capacitor for better efficiency.

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10/17

2010.06 - Rev.A

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