L9925 datasheet(6/9 Pages) STMICROELECTRONICS

6 / 9 page

In this condition the dissipated power is ginen by:

PON =RDS(ON)

⋅ IDS2

The low RDS(ON) of the Multipower BCD process

can provide high currents with low power dissipa-

tion.

OFF STATE

When one of the POWER DMOS transistor is

OFF the VDS voltage is equal to the supply volt-

age and only the leakage current IDSS flows.

The power dissipation during this period is given

by:

POFF =VS

⋅ IDSS

TRANSITIONS

Like all MOS power transistors the DMOS

POWER transistors have an intrinsic diode be-

tween their source and drain that can operate as

a fast freewheeling diode in switched mode appli-

cations. During recirculation with the ENABLE in-

put is low, the POWER MOS is OFF and the di-

ode voltage it is clamped to its characteristics.

When the ENABLE input is low, the POWER

MOS is OFF and the diode carries all of the recir-

culation current. The power dissipated in the tran-

sitional times in the cycle depends upon the volt-

age and current waveforms in the application.

Ptrans =IDS(t)

⋅ VDS(t)

Figure 5a. Two phase chopping

Figure 5b. One phase chopping

Figure 5c. Enable chopping

IN1 = H

IN2 = L

EN1 = H

IN1

IN2

D99AT429

IN1 = L

IN2 = H

EN1 = H

IN1

IN2

D99AT430

IN1 = H

IN2 = L

EN1 = H

IN1

IN2

D99AT431

IN1 = H

IN2 = H

EN1 = H

IN1

IN2

D99AT432

IN1 = H

IN2 = L

EN1 = H

IN1

IN2

D99AT433

IN1 = X

IN2 = X

EN1 = L

IN1

IN2

D99AT434

L9925

6/9

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