MB39A132QN-G-ERE1 Datasheet, PDF (38/56 Pages) Fujitsu Component Limited. – ASSP For Power Management Applications (Rechargeable Battery) Synchronous Rectification DC/DC Converter IC for Charging Li-ion Battery

MB39A132
• Fly-back diode selection
In general, the fly-back diode is not necessary. However, if conversion efficiency becomes a major concern,
it can be improved by adding a fly-back diode.
Select a Schottky barrier diode (SBD) that has a small forward voltage drop.
Since this DC/DC converter control IC adopts synchronous rectification, the length of the time in which
current flows through a fly-back diode is limited by the synchronous rectification period. Therefore, select a
fly-back diode whose current does not exceed the rated peak forward surge current (IFSM). The peak forward
surge current value of the fly-back diode can be found by the following formula.
ΔIL
IFSM ≥ IOMAX +
2
IFSM : Rated value of fly-back diode peak forward surge current [A]
IOMAX : Maximum charge current [A]
ΔIL : Inductor ripple current peak to peak value [A]
The rating of a fly-back diode can be found by the following formula.
VR_Fly > VIN
VR_Fly : DC reverse voltage of fly-back diode [V]
VIN : Switching power supply voltage [V]
38
DS04–27265–3E