BD9137MUV Datasheet, PDF (7/17 Pages) Rohm – High Efficiency Step-down Switching Regulator

・Short-current protection circuit with time delay function
Turns OFF the output to protect the IC from breakdown when the incorporated current limiter is activated continuously for the
fixed time(Hiccup delay) or more. The IC returns to normal operation after Cool down time period has elapsed (self-returning
type).
EN
VOUT
Limit
IL
Output Current in non-control
1/2VOUT
Hiccup delay
1msec
Cool down
time
16m_{～ ～}sec
Output voltage OFF
～～
～～
Output Current in control by limit value
(With fall of the output voltage, limit value goes down)
Standby mode
EN
Operated mode
Cool down
Operated mode
Output voltage OFF
Fig.25 Short-current protection circuit with time delay timing chart
●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 P_Dα 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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