BD9123MUV_12 Datasheet, PDF (13/22 Pages) Rohm – 2.7V to 5.5V, 1.2A 1ch Synchronous Buck Converter integrated FET

BD9123MUV
Datasheet
Advantage 3:
・Supplied in smaller package due to small-sized power MOS FET incorporated.
・Output capacitor Co required for current mode control: 10µF ceramic capacitor
・Inductance L required for the operating frequency of 1 MHz: 4.7µH inductor
Reduces a mounting area required.
VCC
VCC
R PGOOD
Cin
RITH
CITH
DC/DC
Convertor
L
VOUT
Co
L
Co
15mm
RITH
CITH
Fig.32 Example application
20mm
Rf Cf
CIN
RPGOOD
Switching Regulator Efficiency
Efficiency ŋ may be expressed by the equation shown below:
η= ^VOUT×IOUT ×100[%]= ^POUT ×100[%]=
POUT
×100[%]
Vin×Iin
Pin
POUT+PDα
Efficiency may be improved by reducing the switching regulator power dissipation factors PDα as follows:
Dissipation factors:
1) ON resistance dissipation of inductor and FET: PD(I²R)
2) Gate charge/discharge dissipation: PD(Gate)
3) Switching dissipation: PD (SW)
4) ESR dissipation of capacitor: PD (ESR)
5) Operating current dissipation of IC: PD(IC)
1) PD(I²R)=IOUT²Ã—(RCOIL+RON)
(RCOIL[Ω]: DC resistance of inductor, RON[Ω]: ON resistance of FET, IOUT[A]: Output current.)
2) PD(Gate)=Cgs×f×V
(Cgs[F]: Gate capacitance of FET、f[H]: Switching frequency、V[V]: Gate driving voltage of FET)
Vin²Ã—CRSS×IOUT×f
3) PD(SW)=
IDRIVE
(CRSS[F]: Reverse transfer capacitance of FET, IDRIVE[A]: Peak current of gate.)
4) PD(ESR)=IRMS²Ã—ESR
(IRMS[A]: Ripple current of capacitor, ESR[Ω]: Equivalent series resistance.)
5) PD(IC)=Vin×ICC
(ICC[A]: Circuit current.)
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02.MAR.2012 Rev.001