MB3769A Просмотр технического описания (PDF) - Fujitsu

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производитель

MB3769A

SWITCHING REGULATOR CONTROLLER

Fujitsu 

MB3769A

Fig. 5 - MB3769A Equivalent Circuit Over Current Detection Comparator

VREF

To PWM

Comp.

+IN (C)

-IN (C)

Protection element

3. DTC: Dead Time Control (Soft-Start and Quick Shutdown)

The dead time control terminal and the error amplifier output are connected to the PWM comparator.

The maximum duty cycle for VDTC (voltage applied to pin 4) is obtained from the following formula (approximate value at low

frequency):

Duty Cycle = (3.5 - VDTC) x 50 (%) [0% ≤ duty cycle ≤ DMAX (80%)]

The dead time control terminal is used to provide soft start.

In Figure 6, the DTC terminal is connected to the VREF terminal through R and C. Because capacitor C does not charge

instantaneously when the power is turned on, the output transistor is kept turned off. The DTC input voltage and the output pulse

width increase gradually according to the RC time constant so that the control system operates safely.

Fig. 6 - MB3769A Soft Start Function

VREF

C

DTC

R

Soft Start

VREF

C

R1

DTC

R2

Soft Start + DTC

The quick shutdown function prevents soft start malfunction when the power is turned off and on quickly. After the power is shut

down, soft start is disabled because the DTC terminal has low electric potential from the beginning if the power is turned on

again before the capacitor is discharged. The MB3769A prevents this by turning on the discharge transistor to quickly discharge

the capacitor in the stand-by mode.

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