MB3832APFV(1999) データシートの表示（PDF） - Fujitsu

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MB3832APFV
(Rev.:1999)

DC/DC Converter IC for Charging

Fujitsu 

MB3832A

s METHODS OF SETTING THE DEAD TIME AND SOFT START

1. Dead Time

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

a full-ON state (ON duty = 100%) when the power supply is turned on. To prevent this problem, you may determine

the voltage at the DTC pin (pin 16) from the VREF voltage so you can set the output transistor’s dead time

(maximum ON-duty period) as shown in Figure a below.

When the voltage at the DTC pin (pin 16) is higher than the triangular wave output voltage from the oscillator,

the output transistor is turned off. The dead time calculation formula assuming that triangular wave amplitude

.=. 0.6 V and triangular wave minimum voltage .=. 1.3 V is given below.

Duty (ON) .=.

Vdt – 1.3 V

0.6 V

× 100 [%], Vdt =

R2

R1 + R2

×

VREF

When the DTC pin is not used, connect it directly to the VREF pin.

• Figure a Setting the dead time

• Figure b Not setting the dead time

1 VREF

R1

16 DTC

Vdt

R2

1 VREF

16 DTC

2. Soft Start

To prevent surge currents when the IC is turned on, you can set a soft start using the DTC pin (pin 16). You can

also set a soft start along with the dead time by making connections as shown in Figure d below.

• Figure c Setting a soft start

• Figure d Setting the dead time and a soft start

1 VREF

Rdt

16 DTC

Cdt

1 VREF

R1

16 DTC

Cdt

R2

17

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