MB39A113 Datasheet, PDF (29/51 Pages) Fujitsu Component Limited. – ASSP for Power Supply Applications (Secondary Battery)

MB39A113
s SELECTION OF COMPONENTS
• Pch MOS FET
The P-channel MOSFET for switching use should be rated for at least + 20% more than the 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 µPA2714GR (NEC products) is used. Continuity loss, on/off 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)
VD (Max) × ID × tr × fosc
PS (ON) =
6
Off-cycle switching loss : PS (OFF)
VD (Max) × ID (Max) × tf × fosc
PS (OFF) =
6
Total loss : PT
PT = PC + PS (ON) + PS (OFF)
Example) Using the µPA2714GR
Setting 16.8 V
Input voltage VIN = 25 V, output voltage VO = 16.8 V, drain current ID = 3 A, oscillation frequency fosc = 300 kHz,
L = 15 µH, drain-source ON resistance RDS (ON) =: 18 mΩ, tr =: 15 ns, tf =: 42 ns
Drain current (Max) : ID (Max)
VIN−Vo
ID (Max) = Io +
tON
2L
= 3+
25−16.8
2 × 15 × 10^−6
1
×
× 0.672
300 × 10³
=: 3.6 A
Drain current (Min) : ID (Min)
VIN−Vo
ID (Min) = Io −
tON
2L
= 3−
25−16.8
2 × 15 × 10^−6
1
×
× 0.672
300 × 10³
=: 2.4 A
PC = ID2 × RDS (ON) × Duty
= 3² × 0.018 × 0.672
=: 0.109 W
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