HA16107P/FP, HA16108P/FP

Rev.4.00 Jun 15, 2005 page 7 of 39

3. Programming of Maximum ON-Duty (Du Max)

The preceding equations should be used to program the deadband or maximum ON-duty. The following table gives

a summary.

Condition

Triangle

waveform

Du max

Less than 50%

50%

Greater than 50%*

Note:

In a primary-control switching regulator, Du Max > 50% is dangerous because the transformer will saturate.

Soft Start and Quick Shutdown

One purpose of the soft-start function is to protect the switching controller and power MOS FET from surges at power-

up. Another purpose is to let the secondary-side DC voltage rise smoothly.

When power goes off, the quick-shutdown function rapidly discharges the capacitor in the soft-start circuit (and at the

same time switches the PWM output off) to prepare for the next power-on.

The soft-start function in these ICs lets the PWM output develop smoothly from zero to the designated pulse width at

power-up. The soft-start voltage is the 3.8 V voltage value of an internal Zener diode, so the PWM output is able to

start widening gradually as soon as the soft-start function starts operating. The soft-start function will start promptly

The soft-start and quick-shutdown modes are selected automatically in the IC, under control of the UVL signal.