MB39A105 Datasheet, PDF (21/27 Pages) Fujitsu Component Limited. – 1-ch DC/DC Converter IC for low voltage

MB39A105
Example:
L≥
VIN (Max) ²
2IOVO
ton
≥
4²
2 × 0.25 × 9
×
9−4
9
×
1
500 × 10³
≥ 3.95 µH
Inductance values derived from the above formulas are values that provide sufficient margin for continuous
operation at maximum load current, but at which continuous operation is not possible at light loads. It is therefore
necessary to determine the load level at which continuous operation becomes possible. In this application, the
Sumida CMD5D13-6R8 is used. At 6.8 µH, the load current value under continuous operating conditions is
determined by the following formula.
Load current value under continuous operating conditions : IO
IO ≥
VIN (Max) ²
2LVO
ton
≥
4²
2 × 6.8 × 10^−6 × 9
×
9−4
9
×
1
500 × 10³
≥ 145.2 mA
To determine whether the current through the inductor is within rated values, it is necessary to determine the
peak value of the ripple current as well as the peak-to-peak values of the ripple current that affect the output
ripple voltage. The peak value and peak-to-peak value of the ripple current can be determined by the following
formulas.
Peak value : IL
IL ≥
VO × IO
VIN
+
VIN
2L
ton
ton =
VO − VIN
VO
t
Peak-to-peak value : ∆IL
∆IL =
VIN
L
ton
Example: Using the CMD5D13-6R8
6.8 µH (allowable tolerance ±20%) , rated current = 1.4 A
Peak value:
IL ≥
VO × IO
VIN
+
VIN
2L
ton
ton =
VO − VIN
VO
t
≥
9 × 0.25
2.4
+
2.4 × (9 − 2.4)
2 × 6.8 × 10^−6 × 9
×
1
500 × 10³
≥ 1.20 A
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