MB39A112 Datasheet, PDF (21/35 Pages) Fujitsu Component Limited. – 3-ch DC/DC Converter IC

MB39A112
s SELECTION OF COMPONENTS
• Pch MOS FET
The Pch MOS FET for switching use should be rated for at least 20 % or more than the maximum input voltage.
To minimize continuity loss, use a FET with low RDS (ON) between the drain and source. For high input voltage
and high frequency operation, on-cycle switching loss will be higher so that power dissipation must be considered.
In this application, the SANYO MCH3312 and MCH3308 are used. Continuity loss, on/off-cycle switching loss
and total loss are determined by the following formulas. The selection must ensure that peak drain current does
not exceed rated values.
Continuity loss : Pc
PC = ID2 × RDS (ON) × Duty
On-cycle switching loss : PS (ON)
PS (ON) =
VD (Max) × ID × tr × fosc
6
Off-cycle switching loss : PS (OFF)
PS (OFF) =
VD (Max) × ID (Max) × tf × fosc
6
Total loss : PT
PT = PC + PS (ON) + PS (OFF)
Example : Using the MCH3312
• CH1
Input voltage VIN = 12 V, output voltage VO = 1.2 V, drain current ID = 1.5 A, oscillation frequency fOSC = 2350 kHz,
L = 2 µH, drain-source on resistance RDS(ON) =: 180 mΩ, tr =: 2.9 ns, tf =: 8.7 ns.
Drain current (Max) : ID (Max)
ID (Max) = Io +
VIN − Vo
tON
2L
12 − 1.2
= 1.5 +
2 × 2.0 × 10^−6
=: 1.61 A
1
×
2350 × 10³
× 0.1
Drain current (Min) : ID (Min)
ID (Min) = Io−
VIN − Vo
tON
2L
12 − 1.2
= 1.5 −
2 × 2.0 × 10^−6
=: 1.39 A
1
×
2350 × 10³
× 0.1
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