HA16108FP HITACHI [Hitachi Semiconductor], HA16108FP Datasheet - Page 8

• Manufacturer Part Number: HA16108FP
• Description: PWM Switching Regulator for High-performance Voltage Mode Control
• Manufacturer: HITACHI [Hitachi Semiconductor]

HA16107P/FP, HA16108P/FP
3. Programming of Maximum ON-Duty (Du Max)
Condition
Triangle
waveform
Du max
Note: In a primary-control switching regulator, Du Max > 50% is dangerous because the transformer will
Soft Start and Quick Shutdown
One purpose of the soft-start function is to protect the switching controller and power MOSFET 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 even if C
The soft-start and quick-shutdown modes are selected automatically in the IC, under control of the UVL
signal.
8
The preceding equations should be used to program the deadband or maximum ON-duty. The
following table gives a summary.
saturate.
R
Less than 50%
T1
> R
T2
ST
is large.
R
50%
T1
= R
T2
R
Greater than 50%*
T1
< R
T2