bd95710muv-e2 ROHM Co. Ltd., bd95710muv-e2 Datasheet - Page 8

• Manufacturer Part Number: bd95710muv-e2
• Description: 2phase Switching Regulator Controllers Graphic Card
• Manufacturer: ROHM Co. Ltd.

●External Component Selection
※To minimize possible inductor damage and maximize efficiency, choose a inductor with a low (DCR, ACR) resistance.
© 2009 ROHM Co., Ltd. All rights reserved.
BD95710MUV
www.rohm.com
1. Inductor (L) selection
※Passing a current larger than the inductor’s rated current will cause magnetic saturation in the inductor and decrease
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.
2. Output Capacitor (C
Please give due consideration to the conditions in formula (7) below for output capacity, bearing in mind that output rise time
must be established within the soft start time frame.
Note: Improper capacitor may cause startup malfunctions.
3. Input Capacitor (Cin) Selection
A low ESR capacitor is recommended to reduce ESR loss and maximize efficiency.
Output Capacitor
VIN
Output Ripple Current
Input Capacitor
VIN
VIN
Co≦
L
IL
L
L
Cin
3msec×(Limit-IOUT/2)
Co
Co
VOUT
ΔIL
ESR
Co
VOUT
ESL
O
VOUT
) Selection
VOUT
・・・(7)
ΔVOUT=ΔIL×ESR+ESL×ΔIL/T
At least 20mV ripple voltage of the FB voltage is recommended by taking the
equivalent series resistance and inductance into account.
Output ripple voltage is determined as in formula (6) below.
※ In selecting a capacitor, make sure the capacitor rating allows sufficient
margin relative to output voltage. Note that a lower ESR can minimize output
ripple voltage.
(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 (8) below.
IRMS=
Where V
L
: Output ripple current; ESR: C
I
IN
The proper output ripple current setting is about 30% of maximum
output current.
OUT
2
The inductor value is a major influence on the output ripple
current. As formula (3) below indicates, the greater the inductor or
the switching frequency, the lower the ripple current.
=2×V
Limit: Current Limit Value
x
8/20
√
OUT
VOUT(VIN-VOUT)
ΔIL=
ΔIL=0.3×IOUTmax/2. [A]・・・(4)
(ΔI
ESL:equivalent series inductance)
, I
L=
L
RMS
: output ripple current; f: switch frequency)
VIN
=
(VIN-VOUT) x VOUT
(VIN-VOUT) x VOUT
IOUT
ON
ΔIL x VIN x f
4
L x VIN x f
・・・(6)
O
equivalent series resistance,
[A]・・・(8)
[H]・・・(5)
[A]・・・(3)
Technical Note
2009.04 - Rev.B