MB39A102 View Datasheet(PDF) - Fujitsu

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Description

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MB39A102

4-ch DC/DC Converter IC

Fujitsu 

MB39A102

■ SETTING THE DEAD TIME

When the device is set for step-up inverted output based on the step-up or step-up/down Zeta conversion, step-

up/down Sepic conversion or flyback conversion, the FB terminal voltage may reach and exceed the triangular

wave voltage due to load fluctuation. If this is the case, the output transistor is fixed to a full-ON state

(ON duty = 100 %). To prevent this, set the maximum duty of the output transistor. To set it, set the voltage at

the DTC terminal by applying a resistive voltage divider to the VREF voltage as shown below.

When the DTC terminal voltage is higher than the triangular wave voltage, the output transistor is turned on.

The maximum duty calculation formula assuming that triangular wave amplitude =: 0.5 V and triangular wave

lower voltage =: 0.4 V is given below.

DUTY

(ON)

Max=:

Vdt − 0.4

0.5 V

V

× 100 (%) , Vdt =

Rb

Ra + Rb

× VREF

When the DTC terminal is not used, connect it directly to the VREF terminal (pin 7) as shown below (when no

dead time is set).

• When using DTC to set dead time

7 VREF

DTCx

Ra

Rb

Vdt

• When no dead time is set

7 VREF

x : Each channel No.

DTCx

x : Each channel No.

19

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