MB39A125 Datasheet, PDF (54/64 Pages) Fujitsu Component Limited. – DC/DC Converter IC for Charging Li-ion Battery

MB39A125/126
Peak-to-peak Value
16.8 V output
VIN − Vo
∆IL =
tON
L
25 − 16.8
1
=
×
× 0.672
15 × 10^−6
300 × 10³
=: 1.22 A
12.6 V output
VIN − Vo
∆IL =
tON
L
22 − 12.6
1
=
×
× 0.572
15 × 10^−6
300 × 10³
=: 1.2 A
• Flyback diode
Shottky barrier diode (SBD) is generally used for the flyback diode when the reverse voltage to the diode is less
than 40V. The SBD has the characteristics of higher speed in terms of faster reverse recovery time, and lower
forward voltage, and is ideal for achieving high efficiency. As long as the DC reverse voltage is sufficiently higher
than the input voltage, and the mean current flowing during the diode conduction time is within the mean output
current level, and as the peak current is within the peak surge current limits, there is no problem. In this application
the ROHM RB053L-30 are used. The diode mean current and diode peak current can be obtained by the following
formulas.
Diode mean current : IDi
Vo
IDi ≥ Io × (1 −
)
VIN
Diode peak current : IDip
IDip ≥
(Io +
Vo
tOFF)
2L
Example) Using the RB053L-30
VR (DC reverse voltage) = 30 V, mean output current = 3.0 A, peak surge current = 70 A,
VF (forward voltage) = 0.42 V, at IF = 3.0 A
16.8 V output
Vo
IDi ≥ Io × (1 −
)
VIN
≥ 3 × (1 − 0.672)
≥ 0.984 A
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