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BD9130EFJ Datasheet(PDF) 9 Page - Rohm

No. de Pieza. BD9130EFJ
Descripción  Output 2A or More High-efficiency Step-down Switching Regulator with Built-in Power MOSFET
Descarga  15 Pages
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Fabricante  ROHM [Rohm]
Página de inicio  http://www.rohm.com
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BD9130EFJ Datasheet(HTML) 9 Page - Rohm

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BD9130EFJ
Technical Note
9/14
www.rohm.com
2009.05 - Rev.A
© 2009 ROHM Co., Ltd. All rights reserved.
Selection of components externally connected
1. Selection of inductor (L)
Fig.27 Output ripple current
* 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=3.3V, VOUT=1.8V, f=1MHz, ΔIL=0.2×2A=0.4A, for example,(BD9130EFJ)
* 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)
3. Selection of input capacitor (Cin)
Fig.29 Input capacitor
A low ESR 10µF/10V ceramic capacitor is recommended to reduce ESR dissipation of input capacitor for better efficiency.
Fig.28 Output capacitor
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.
ΔIL=
(VCC-VOUT)×VOUT
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)
L=
(VCC-VOUT)×VOUT
ΔIL×VCC×f
[H]・・・(3)
(ΔIL: Output ripple current, and f: Switching frequency)
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):
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 22μF to 100μF ceramic capacitor is recommended.
Less ESR allows reduction in output ripple voltage.
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):
IRMS=IOUT×
VOUT(VCC-VOUT)
VCC
[A]・・・(5)
When Vcc is twice the VOUT, IRMS=
IOUT
2
(3.3-1.8)×1.8
0.4×3.3×1M
L=
=2.05μ → 2.2[μH]
< Worst case > IRMS(max.)
IRMS=2×
1.8(3.3-1.8)
3.3
=0.99[ARMS]
ΔIL
VCC
IL
L
Co
VOUT
IL
VCC
L
Co
VOUT
ESR
VCC
L
Co
VOUT
Cin
If VCC=3.3V, VOUT=1.8V, and IOUTmax.=2A, (BD9130EFJ)


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