MB39C308 Datasheet, PDF (36/60 Pages) Fujitsu Component Limited. – 6ch DC/DC Converter IC for LPIA Platform VR

MB39C308
High-side FET switching power dissipation
PSW =
VDD × fOSC × (Ibtm × tr + Itop × tf)
2
PSW : SW power dissipation [W]
VDD : Switching system power supply voltage [V]
fOSC : Oscillation frequency (Hz)
Ibtm : Inductor ripple current bottom value [A]
Itop : Inductor ripple current top value [A]
tr : High-side FET turn-on time [s]
tf : High-side FET turn-off time [s]
tr and tf are simply given by the following values.
tr = 4 ns
tf = 4 ns
The power dissipation of the Low-side FET can be found from the following formula.
PRon = (IOMAX)² × (1 −
VO
) × Ron
VDD
PRon : Low-side FET conducting power dissipation [W]
IoMAX : Maximum load current [A]
VDD : Switching system power supply voltage [V]
VO : Output setting voltage [V]
Ron : Low-side FET on resistance [Ω]
Note : The transition voltage of the voltage between the drain and source of the Low-side FET is generally small
and the switching power loss is negligible. Therefore it has been omitted from this formula.
The junction temperature (Tj) can be found from the following formula.
Tj = Ta + θja × PIC
Tj : Junction temperature [ °C] ( + 125 °C Max)
Ta : Ambient temperature [ °C]
θja : PFBGA-208 package thermal resistance (34 °C/W)
PIC : IC power dissipation [W]
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DS04-27261-6E