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3.4 SLOW DECAY MODE

Figure 14 shows the operation of the bridge in the Slow Decay mode during the Off Time. At any time only two

legs of the three-phase bridge are active, therefore only the two active legs of the bridge are shown in the figure

and the third leg will be off. At the start of the Off Time, the lower power MOS is switched off and the current

recirculates around the upper half of the bridge. Since the voltage across the coil is low, the current decays slow-

ly. After the Dead Time the upper power MOS is operated in the synchronous rectification mode reducing the

impendence of the freewheeling diode and the related conducting losses. When the monostable times out, up-

per MOS that was operating the synchronous mode turns off and the lower power MOS is turned on again after

some delay set by the Dead Time to prevent cross conduction.

Figure 14. Slow Decay Mode Output Stage Configurations

0.1

1

10

100

1

10

100

Coff [nF]

1.5

µs (typ. value)

A) ON TIME

B) 1

µs DEAD TIME

C) SYNCHRONOUS

RECTIFICATION

D) 1

µs DEAD TIME

D01IN1336