Technical Note

10/17

www.rohm.com

2011.01 - Rev.A

© 2011 ROHM Co., Ltd. All rights reserved.

BD9123MUV

・

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

UVLO.

Fig.32 Short-current protection circuit with time delay timing chart

●

Switching regulator efficiency

Efficiency ŋ may be expressed by the equation shown below:

Dissipation factors:

1) ON resistance dissipation of inductor and FET: PD(I

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(I

2) PD(Gate)=Cgs×f×V

(Cgs[F]: Gate capacitance of FET、f[H]: Switching frequency、V[V]: Gate driving voltage of FET)

η

=

Vin×Iin

×

100[%]=

Pin

×

100[%]=

×

100[%]

Output voltage OFF Latch

VCC

Output Short circuit

Threshold Voltage

Output voltage

OFF

Operated mode

Operated mode

UVLO

Timer Latch

UVLO

Output voltage

OFF

Vin

3) PD(SW)=