Technical Note
12/18
www.rohm.com
2009.08 - Rev.A
?2009 ROHM Co., Ltd. All rights reserved.
BD9153MUV
?SPAN class="pst BD9153MUV-E2_2471427_7">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.
If VCC=5.0V, VOUT=1.2V, f=1.0MHz, 擨L=0.3?.5A=0.45A, for example,(BD9153MUV)
;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)
The inductance significantly depends on output ripple current.
s seen in the equation (1), the ripple current decreases as the
inductor and/or switching frequency increases.
擨L=
(VCC-VOUT)譜OUT
L譜CC譮
A?
ppropriate ripple current at output should be 20% more or less of
the maximum output current.
擨L=0.2譏OUTmax. [A]?2)
L=
(VCC-VOUT)譜OUT
擨L譜CC譮
H?
(擨L: 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)
擵OUT=擨L譋SR [V]?4)
(擨L: Output ripple current, ESR: Equivalent series resistance of output capacitor)
;Rating of the capacitor should be determined allowing sufficient margin against
output voltage. A 22礔 to 100糉 ceramic capacitor is recommended.
Less ESR allows reduction in output ripple voltage.
Fig.36 Output capacitor
5-1.2?.2
0.45??.0M
L=
=2.02??2.2[糎]
擨L
V
OUT
Fig.35 Output ripple current
IL
VCC
IL
L
Co
VCC
L
Co
VOUT
ESR
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