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BD9139MUV Datasheet, PDF (8/17 Pages) Rohm – Output 2A or More High-efficiency Step-down Switching Regulators with Built-in Power MOSFET | |||
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BD9139MUV
Technical Note
ã»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
VOUT
Limit
IL
1msec
Output Current in non-control 1/2VOUT
Until output voltage goes up the half of Vo or over,
timer latch is not operated.
(No timer latch, only limit to the output current)
Output voltage OFF Latch
Output Current in control by limit value
(With fall of the output voltage, limit value goes down)
Standby mode
EN
Operated mode
Standby mode
Operated mode
Timer Latch
EN
Fig.25 Short-current protection circuit with time delay timing chart
âSwitching regulator efficiency
Efficiency Å may be expressed by the equation shown below:
η= VOUTÃIOUT Ã100[%]= POUT Ã100[%]=
POUT
Ã100[%]
VinÃIin
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 FETï¼PD(I2R)
2) Gate charge/discharge dissipationï¼PD(Gate)
3) Switching dissipationï¼PD(SW)
4) ESR dissipation of capacitorï¼PD(ESR)
5) Operating current dissipation of ICï¼PD(IC)
1)PD(I2R)=IOUT2Ã(RCOIL+RON) (RCOIL[Ω]ï¼DC resistance of inductor, RON[Ω]ï¼ON resistance of FET, IOUT[A]ï¼Output
current.)
2)PD(Gate)=CgsÃfÃV (Cgs[F]ï¼Gate capacitance of FET, f[H]ï¼Switching frequency, V[V]ï¼Gate driving voltage of FET)
Vin2ÃCRSSÃIOUTÃf
3)PD(SW)=
(CRSS[F]ï¼Reverse transfer capacitance of FET, IDRIVE[A]ï¼Peak current of gate.)
IDRIVE
4)PD(ESR)=IRMS2ÃESR (IRMS[A]ï¼Ripple current of capacitor, ESR[Ω]ï¼Equivalent series resistance.)
5)PD(IC)=VinÃICC (ICC[A]ï¼Circuit current.)
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8/16
2009.05 - Rev.A
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