MB39C308 Datasheet, PDF (35/60 Pages) Fujitsu Component Limited. – 6ch DC/DC Converter IC for LPIA Platform VR

MB39C308
• Power Dissipation and Thermal Design
Although these does not need to be examined in most cases because the IC is highly efficient, Dissipation and
the thermal design may need to be investigate if the IC is used with high power supply voltages, high oscillator
frequencies, high loads, or at high temperatures.
The internal IC power dissipation (PIC) can be found from the following formula.
PIC = VDD × (IDD + Qg12 + 32 × 10^-9) × fOSC + PHisideFET3-6 + PLosideFET3-6
PIC
: Internal IC power dissipation [W]
VDD
: Power supply voltage (VIN) [V]
IDD
: Power supply current [A] (250 μA Typ)
Qg12
: Total gate charge of High-side FET (VGS = 4.3 V) and Low-side FET (VGS = 5 V) for CH1 and CH2 [C]
fOSC
: Switching frequency [Hz]
PHisideFET3-6 : Total High-side SWFET power dissipation of internal High-side FET [W]
PLosideFET3-6 : Total Low-side SWFET power dissipation of internal Low-side FET [W]
Furthermore, the power dissipation of the High-side FET of each built-in channel can be found from the following
formula.
PHisideFET = PRON + PSW
PHisideFET : High-side FET power dissipation [W]
PRON : High-side FET conducting power dissipation [W]
PSW : High-side FET switching power dissipation [W]
High-side FET conducting power dissipation
VO
PRON = (IoMAX) ²
VDD
× RON
PRON : High-side FET conducting power dissipation [W]
IoMAX : Maximum load current [A]
VDD : Switching power supply voltage [V]
VO : Output setting voltage [V]
RON : On resistance of High-side FET [Ω]
DS04-27261-6E
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