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© 2019 ROHM Co., Ltd.
No. 61UG024E Rev.002
Jul. 2021
User’s Guide
BM2P141X-EVK-001
Design Overview
1 Important parameter
V
IN
: Input Voltage Range AC 90 V ~ 264 Vac (DC 100 V ~ 380 V)
V
OUT
: Output Voltage DC 14 V
I
OUT
(Typ)
: Constant Output Current 0.5 A
I
OUT
(Max)
: Maximum Output Current 0.715 A
f
SW
: Switching Frequency Min:60 kHz, Typ:65 kHz, Max:70 kHz
Ipeak(Min) : Over Current Detection Current Min:1.8 A, Typ:2.0 A, Max:2.2A
2 Coil Selection
2.1 Determining Coil Inductance
The switching operation mode determines the L value so that it becomes as discontinuous mode (DCM) as possible. In the
continuous mode (CCM), reverse current in trr of the diode flows, which leads to an increase in power loss of diode.
Furthermore, this reverse current becomes the peak current when the MOSFET is ON, and the power loss of the MOSFET also
increases. The constant load current I
OUT
(Typ): 0.5 A, the peak current I
L
flowing through the inductor is:
𝐼
𝐿
= 𝐼
𝑂𝑈𝑇
(𝑇𝑦𝑝) × 2 = 1.0
[A]
It tends to be in continuous mode (CCM) when the input voltage drops.
Calculate with input voltage minimum voltage 100 Vdc
with 20% margin and V
IN
(Min) = 80 Vdc.
From the output voltage V
OUT
: 14 V and the diode V
F
: 1 V,
Calculate the maximum value of Duty: Duty (Max).
Duty(𝑚𝑎𝑥) =
𝑉
𝑂𝑈𝑇
+ 𝑉
𝐹
𝑉
𝐼𝑁
(𝑀𝑖𝑛)
= 0.188
Figure 8. Coil current waveform at OCP detection
From the minimum switching frequency f
SW
(Min) = 60 kHz,
Calculate on time ton (Max)
ton(𝑀𝑎𝑥) =
𝐷𝑢𝑡𝑦(𝑀𝑎𝑥)
𝑓
𝑆𝑊
(𝑀𝑖𝑛)
= 3.125
[μsec]
Calculate L value to operate in discontinuous mode.
L < ton(𝑀𝑎𝑥) ×
𝑉
𝐼
(𝑀𝑖𝑛)−𝑉𝑜
𝐼
𝐿
= 206.3
[μH]
t
t
ON
I
omax
IL
I
L
I
p
I
peak
t
dly
OCP Detection
I
ripple
Δ
I
L
