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© 2019 ROHM Co., Ltd.
No. 61UG024E Rev.002
Jul. 2021
User’s Guide
BM2P141X-EVK-001
2.2 Inductor Current Calculation -Continued
When it is applied to the formula of the peak current,
𝐼𝑝 = 𝐼
𝑂𝑈𝑇
(𝑀𝑎𝑥) +
𝐼𝑟𝑖𝑝𝑝𝑙𝑒
2
= 𝐼
𝑂
+
{𝑉
𝐼𝑁
(𝑀𝑎𝑥)−(𝑉
𝑂𝑈𝑇
+𝑉
𝐹
)}(𝑉
𝑂𝑈𝑇
+𝑉
𝐹
)
2×𝐿×𝑉
𝐼𝑁
(𝑀𝑎𝑥)×𝑓
𝑆𝑊
(𝑀𝑖𝑛)
= 1.52
[A]
Select a coil with an allowable current of 1.52 A or more.
In this EVK, we use inductance value: 150 μH, rated: 1.9 A product.
Radial inductor (closed magnetic circuit type)
Core size DR09 x 11 series
Product:
XF1501Y-151
Manufacturer: ALPHA TRANS CO,. LTD
〒
541-0059
Senbanishi KID Bldg 7F, 4-4-11, Bakurou-machi, Chuo-ku, Osaka
3 Diode Selection
3.1 Flywheel Diode : D1
Flywheel diode uses fast diode (fast recovery diode).The reverse voltage of the diode is V
IN
(Max): 380 V when the output
voltage at startup is 0 V. Consider the derating and select 600 V diode. The condition where the effective current of the diode is
maximized is when the input voltage is the maximum voltage V
IN
(Max): 380 V, the maximum load current Io (Max): 0.715 A,
and the switching frequency is 60 kHz at the minimum.
𝐷𝑢𝑡𝑦 =
𝑉
𝑂𝑈𝑇
+𝑉
𝐹
𝑉
𝐼𝑁
(𝑀𝑎𝑥)
= 3.9
[%]
The average current ID of the diode is calculated from the peak current Ip: 1.52 A by the following formula
𝐼
𝐷
(𝑟𝑚𝑠) = 𝐼𝑝 × √
1−𝐷𝑢𝑡𝑦
3
= 0.860
[A]
Select the rated current of 0.860 A or more.
In fact, we used RFN5BM6S of 5 A / 600 V product as a result of mounting the board and considering the parts temperature.
3.2 VCC Rectifier Diode : D1
Rectifier diodes are used for diodes to supply VCC. The reverse voltage applied to the diode is V
IN
(Max): 380 V. Consider the
derating and select 600 V diode
.
Because the current flowing to the IC is small enough, we use the 0.2 A / 600 V
RRE02VSM6S.
