bd95500muv ROHM Co. Ltd., bd95500muv Datasheet - Page 12

• Manufacturer Part Number: bd95500muv
• Description: Switching Regulator With Mosfet Ddr-sdram Cores
• Manufacturer: ROHM Co. Ltd.

●External Component Selection
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BD95500MUV
www.rohm.com
2. Output Capacitor (C
1. Inductor (L) selection
3. Input Capacitor (Cin) Selection
PGND
HG
PGND
HG
LG
LG
※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.
Note: Improper capacitor may cause startup malfunctions
A low ESR capacitor is recommended to reduce ESR loss and maximize efficiency.
PGND
HG
LG
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.
Co≦
Input Capacitor
SW
SW
Output Capacitor
Output Ripple Current
VIN
VIN
SW
TSS×(Limit-I
VIN
L
L
IL
L
Cin
V
OUT
O
) Selection
Co
ΔIL
OUT
Co
VOUT
ESR
ESL
Co
)
VOUT
VOUT
・・・(8)
When determining the proper output capacitor, be sure to factor in the equivalent
series resistance and equivalent series inductance required to set the output ripple
voltage 20mV or more.
In selecting the limit of inductor, be sure to allow enough margin for output voltage.
Output ripple voltage is determined as in formula (7) below.
ΔV
(ΔI
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.
ESL: equivalent series inductance)
L
IRMS=I
Where V
OUT
: Output ripple current; ESR: C
=ΔI
OUT
L
IN
×ESR + ESL×ΔI
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 (5) below indicates, the greater the inductor or the
switching frequency, the lower the ripple current.
=2×V
Tss: Soft start time (See formula (2) in P10)
Limit: Over current detection (See formula (10)(11) in P13)
×
12/20
√
OUT
V
ΔI
ΔI
(ΔI
IN
, IRMS=
L
L
L=
(V
L
=
=0.3×I
: output ripple current; f: switch frequency)
V
IN
IN
-V
(V
(V
L
OUT
IN
IN
/ T
OUT
-V
L×V
L×V
-V
I
O
)
OUT
ON
OUT
2
OUT
max. [A]・・・(5)
equivalent series resistance,
・・・(7)
IN
IN
[A]・・・(9)
)×V
)×V
×f
×f
OUT
OUT
[H]・・・(6)
[A]・・・(4)
Technical Note
2010.05 - Rev.C