8/16

Technical Note

Timing chart

(BD9781HFP)

-

While in basic operation mode

-

While in overcurrent protection mode

FB

SW

EN/SYNC

Internal

OSC

Fig.27

Fig.28

External synchronizing function (BD9781HFP)

In order to activate the external synchronizing function, connect the frequency setting resistor to the RT pin and then input

a synchronizing signal to the EN/SYNC pin. As the synchronizing signal, input a pulse wave higher than a frequency determined

with the setting resistor (RT). On the BD9781HFP, design the frequency difference to be within 50%. Furthermore,

set the pulse wave duty between 10% and 90%.

Fig.29

Internal

OSC

: For RT only

: For external

synchronization

Output short circuit

FB

SW

Internal

OSC

Auto reset

Auto reset

Auto reset

Auto reset

2010.02 -

Rev. B

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BD9778F, BD9778HFP, BD9001F, BD9781HFP