MB39A132QN-G-ERE1 Datasheet, PDF (35/56 Pages) Fujitsu Component Limited. – ASSP For Power Management Applications (Rechargeable Battery) Synchronous Rectification DC/DC Converter IC for Charging Li-ion Battery

MB39A132
■ APPLICATION NOTE
• Inductor selection
As a rough guide, the inductance of an inductor should keep the peak-to-peak value of inductor ripple current
below 50% of the maximum charge current. The inductance fulfilling the above condition can be found by
the following formula.
VIN − VO
VO
L≥
×
LOR × IOMAX
VIN × fOSC
L : Inductance [H]
IOMAX : Maximum charge current [A]
LOR : Inductor ripple current peak to peak value - Maximum charge current ratio (0.5)
VIN : Switching power-supply voltage [V]
VO : Charge voltage [V]
fOSC : Switching frequency [Hz]
The minimum charge current (critical current) in the condition that inductor current does not flow in reverse
can be found by the following formula.
IOC =
VO
2×L
VIN − VO
×
VIN × fOSC
IOC : Critical current [A]
L : Inductance [H]
VIN : Switching power-supply voltage [V]
VO : Charge voltage [V]
fOSC : Switching frequency [Hz]
The maximum value of the current flowing through the inductor needs to be found in order to determine
whether the current flowing through the inductor is within the rated value. The maximum current flowing
through the inductor can be found by the following formula.
ΔIL
ILMAX ≥ IoMAX +
2
ILMAX : Maximum inductor current [A]
IOMAX : Maximum charge current [A]
ΔIL : Inductor ripple current peak to peak value [A]
VIN − VO
VO
ΔIL ≥
×
L
VIN × fOSC
Inductor current
ILMAX
IoMAX
IOC
0
The current is shifting according to the charge current.
ΔIL
Time
DS04–27265–3E
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