BD9141MUV Datasheet, PDF (9/19 Pages) Rohm – Output 2A or More High-efficiency Step-down Switching Regulator with Built-in Power MOSFET

BD9141MUV
Technical Note
・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(TLATCH) or more. The output thus held tuned OFF may be recovered by restarting EN or by re-unlocking
UVLO.
EN
Output Short circuit
Threshold Voltage
VOUT
IL Limit
IL
Standby
mode
EN
Output OFF
latch
t1<TLATCH
Operating mode
t2=TLATCH
Standby
mode
Operating mode
Timer latch
EN
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 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)= ^{Vin2×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
© 2009 ROHM Co., Ltd. All rights reserved.
9/18
2009.06 - Rev.A