MB39A132QN-G-ERE1 Datasheet, PDF (39/56 Pages) Fujitsu Component Limited. – ASSP For Power Management Applications (Rechargeable Battery) Synchronous Rectification DC/DC Converter IC for Charging Li-ion Battery

MB39A132
• Output capacitor selection
Since a high ESR causes the output ripple voltage to increase, a low-ESR capacitor is needs to be used in
order to reduce the output ripple voltage. Use a capacitor that has sufficient ratings to surge current generated
when the battery is inserted or removed. Generally, the ceramic capacitor is used as the output capacitor.
With the switching ripple voltage taken into consideration, the minimum capacitance required can be found
by the following formula.
1
Co ≥
2π × fosc × (ΔVO/ΔIL − ESR)
Co : Output capacitance [F]
ESR : Series resistance element of output capacitance [Ω]
ΔVO : Switching ripple voltage [V]
ΔIL : Inductor ripple current peak to peak value [A]
fosc : Switching frequency [Hz]
Since an overshoot occurs in the DC/DC converter output voltage when a battery being charged is removed,
use a capacitor having sufficient withstand voltage. Generally, the capacitor having a rated withstand voltage
higher than the maximum input voltage is sued.
Moreover, use a capacitor having sufficient tolerance for allowable ripple current. The allowable ripple current
required can be found by the following formula.
ΔIL
Irms ≥
2√3
Irms : Allowable ripple current (Root-mean-square value) [A]
ΔIL : Inductor ripple current peak-to-peak value [A]
DS04–27265–3E
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