MB39A113 Datasheet, PDF (31/51 Pages) Fujitsu Component Limited. – ASSP for Power Supply Applications (Secondary Battery)

MB39A113
PS (ON) =
=
=:
VD × ID × tr × fosc
6
22 × 3 × 15 × 10^−9 × 300 × 10³
6
0.050 W
VD × ID (Max) × tf × fosc
PS (OFF) =
6
22 × 3.6 × 42 × 10^−9 × 300 × 10³
=
6
=: 0.166 W
PT = PC + PS (ON) + PS (OFF)
=: 0.093 + 0.050 + 0.166
=: 0.309 W
The above power dissipation figures for the µPA2714GR are satisfied with ample margin at 2.0 W.
• Inductor
In selecting inductors, it is of course essential not to apply more current than the rated capacity of the inductor,
but also to note that the lower limit for ripple current is a critical point that if reached will cause discontinuous
operation and a considerable drop in efficiency. This can be prevented by choosing a higher inductance value,
which will enable continuous operation under light-load.
Note that if the inductance value is too high, however, direct current resistance (DCR) is increased and this will
also reduce efficiency. The inductance must be set at the point where efficiency is greatest.
Note also that the DC superimposition characteristic becomes worse as the load current value approaches the
rated current value of the inductor, so that the inductance value is reduced and ripple current increases, causing
loss of efficiency.
The selection of rated current value and inductance value will vary depending on where the point of peak efficiency
lies with respect to load current.
Inductance values are determined by the following formulas.
The L value for all load current conditions is set so that the peak to peak value of the ripple current is 1/2 the
load current or less.
Inductance value : L
2 (VIN−Vo)
L≥
tON
Io
16.8 V output
Example)
2 (VIN (Max) −Vo)
L≥
tON
Io
2 × (25−16.8)
1
≥
×
× 0.672
3
300 × 10³
≥ 12.2 µH
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