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© 2018 ROHM Co., Ltd.
No. 60UG092E Rev.001
JULY.2018
User’s Guide
BM2P0161-EVK-003
Ripple Current Is (rms) is
Is rms = Ispk × @
1 − 4* 5
3
=
77
14 × 0.9828 ×
@1 − 0.212
3
= 2.7688
C13 charge/Discharge Current Ic (rms) is
Ic rms = t O=
6
−
6
= t2.768
6
− 2
6
= 1.918 O=
The capacitor’s withstand voltage should be set to about twice the output voltage.
Vout x 2 = 12V x 2 = 24V
→
over 25V
Select an electrolytic capacitor that is suitable for these conditions.
The board is select capacitor as bellows.
C13 1000uF/25V
Rubycon ZLJ Series Iripple 2500mA@100kHz Imp 0.028
Ω
C15
0.1uF/50V
Ceramic Capacitor
（＊）
Use the actual equipment to check the actual ripple-voltage, ripple-current
and capacitor-current.
2-10
．
Output voltage setting resistors: R10,R11,R12
Set the output voltage with the following formal
When Shunt regulator IC2: Vref=2.495V,
Vo = u1 +
10 + 11
12
v × Vref = u1 +
33kΩ + 5.6kΩ
109Ω
v × 2.495V = 12.1257V
2-11
．
Parts for adjustment of control circuit:R15, C16, R13, R14
R15 and C11 are parts for phase compensation. Approximately R15:1k to 30k
Ω
, C11=0.1uF, and adjust them while they are
assembled in the product.
R13 is a resistor which limits a control circuit current. Approximately R14:300 to 2k
Ω
, and adjust it while it assembled in the
product. R14 is a resistor for adjustment of minimum operating current of shunt regulator IC2.
In case of IC2: TL431, minimum operating current is 1mA. And when Optocoupler:PC1_Vf is 1V, R14 = 1V / 1mA = 1k
Ω
3
．
EMI Measure
Confirm the following with regard to EMI countermeasures.
(*) Constants are reference values. Need to be adjusted based on noise effects.
- Addition of filter to input block C1, C2, LF1
- Addition of capacitor between primary-side and secondary-side (approximately C11: Y-Cap
2200pF)
- Addition of RC snubber to secondary diode
