BD91361MUV Datasheet, PDF (9/18 Pages) Rohm – Output 2A More High-efficiency Step-down Switching Regulator with Built-in Power MOS FET

BD91361MUV
Technical Note
●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)
3)PD(SW)=
Vin²Ã—CRSS×IOUT×f
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.)
www.rohm.com
© 2010 ROHM Co., Ltd. All rights reserved.
9/17
2010.06 - Rev.A