MB3825 datasheet(29/39 Pages) FUJITSU

No de pièce	MB3825

Description	6-ch DC/DC Converter IC With Synchronous Rectifier

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Fabricant	FUJITSU [Fujitsu Component Limited.]

Site Internet	http://edevice.fujitsu.com/fmd/en/index.html

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MB3825A

29

s METHOD OF SETTING THE DEAD TIME

When the device is set for step-up inverted output based on the flyback method, the output transistor is fixed to

full-on state (ON-duty = 100 %) at power switch-on.To prevent this problem, you may determine the voltages on the

DTC3 terminal (pin 31) from the VREF voltage so you can easily set the output transistor’s dead time (maximum ON-

duty) independently for each channel as shown Figure.12.

When the voltage on the DTC3 terminal is lower than the triangular-wave (CT1) output voltage from the oscillator,

the output transistor turns off. The dead time calculation formula assuming that triangular-wave amplitude := 0.7 V

and triangular-wave maximum voltage := 1.35 V is given below.

When you do not use this DTC3 terminal, connect then to VREF terminal (pin 27) as shown Figure.13..

Duty (ON) MAX :=

× 100 [%]

Vdt – 0.65

0.7

27

31

VREF

DTC3

Vdt

Rb

Ra

Figure 12. When using DTC to set dead time

27

31

VREF

DTC3

Figure 13. When not using DTC to set dead time

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