BD95242MUV ROHM Electronics, BD95242MUV Datasheet - Page 11

• Manufacturer Part Number: BD95242MUV
• Description: 2ch Switching Regurators for Desktop PC
• Manufacturer: ROHM Electronics

● External Component Selection
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www.rohm.com
Co+C
1. Inductor (L) selection
2.Output Capacitor (C
3. Input Capacitor (Cin) Selection
※Passing a current larger than the inductor’s rated current will cause magnetic saturation in the inductor and decrease
※To minimize possible inductor damage and maximize efficiency, choose a inductor with a low (DCR, ACR) resistance.
Please give due consideration to the conditions in formula (8) below for output capacity, bear in mind that output rise time
must be established within the soft start time frame.
A low ESR capacitor is recommended to reduce ESR loss and maximize efficiency.
Output ripple current
VIN
system efficiency. In selecting the inductor, be sure to allow enough margin to assure that peak current does not exceed
the inductor rated current value.
Output Capacitor
Input Capacitor
Note: Improper capacitor may cause startup malfunctions.
V
V
EXT
IN
IN
L
I
L
L
L
≦
Cin
T
SS
Co
Co
×(Limit-I
V
OUT
ΔI
V
ESR
Co
OUT
L
O
C
) Selection
V
EXT
OUT
OUT
)
Load
VOUT
・・・(8)
When determining the proper output capacitor, be sure to factor in the equivalent
series resistance required to smooth out ripple volume and maintain a stable
output voltage range.
Output ripple voltage is determined as in formula (7) below.
ΔV
(ΔI
※ In selecting a capacitor, make sure the capacitor rating allows sufficient
The input capacitor selected must have low enough ESR resistance to fully
support large ripple output, in order to prevent extreme over current. The
formula for ripple current IRMS is given in (9) below.
L
margin relative to output voltage. Note that a lower ESR can minimize output
ripple voltage.
I
Where V
OUT
RMS
: Output ripple current; ESR: C
=ΔI
=I
OUT
L
IN
×ESR [V]・・・(7)
The proper output ripple current setting is about 30% of maximum
output current.
The inductor value is a major influence on the output ripple
current. As formula (4) below indicates, the greater the inductor or
the switching frequency, the lower the ripple current.
×
=2×V
Tss: Soft start time
Limit: Over current detection 2A(Typ)
11/20
√
OUT
V
ΔI
ΔI
(ΔI
IN
, IRMS=
(V
L
L
L=
L
=
=0.3×I
: output ripple current; f: switch frequency)
IN
V
-V
IN
(V
(V
OUT
IN
IN
ΔI
OUT
-V
-V
L×V
)
O
L
OUT
OUT
I
×V
max. [A]・・・(5)
OUT
equivalent series resistance)
2
IN
)×V
)×V
IN
×f
×f
[A]・・・(9)
OUT
OUT
[H]・・・(6)
[A]・・・(4)
Technical Note
2009.04 - Rev.B