MB39A119 Datasheet, PDF (40/53 Pages) Fujitsu Component Limited. – DC/DC Converter IC of Synchronous Rectification for charging Li-ion battery

MB39A119
2. Inductor (CDRH104R-5R2 : SUMIDA product)
5.2 µH (tolerance ± 30%) , rated current = 5.5 A
2 (VIN−Vo)
L≥
tON
Io
2 × (24−12.6)
1
≥
×
× 0.63
4.0
500 × 10³
≥ 4.67 µH
The load current satisfying the continuous current condition
Vo
Io ≥
tOFF
2L
12.6
1
≥
×
× (1−0.63)
2 × 5.2 × 10^−6
500 × 10³
≥ 897.0 mA
IL ≥ IO
VIN−Vo
tON
2L
20−12.6
1
≥ 4.0 +
×
× 0.63
2 × 5.2 × 10^−6 500 × 10³
≥ 4.90 A
Ripple current : Peak-to-peak value
If the peak-to-peak ripple current is ∆IL, it is obtained by the following formula.
VIN−Vo
∆IL =
tON
L
20−12.6
1
=
×
× 0.63
5.2 × ^−6
500 × 10³
=: 1.79 A
3. Diode for bootstrap (SBS006 : SANYO product)
VR (DC reverse voltage) = 30 V, Average output current = 500 mA, peak surge current = 10 A
VF (forward voltage) = 0.35 V, at IF = 300 mA
VR : value that satisfies input voltage
Efficiency is somewhat rising in low leak Schottky diode by the use but even if the signal diode is used, it
is enough. It is recommended to use low VF. Also, capacitor for bootstrap must be very large than gate
capacity of FET at main side. It is recommended to use the capacity of approximately 0.1 µF to 1.0 µF.
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