ha16158 Renesas Electronics Corporation., ha16158 Datasheet - Page 12

• Manufacturer Part Number: ha16158
• Description: Pfc & Pwm Control Ic
• Manufacturer: Renesas Electronics Corporation.

HA16158P/FP
2. Soft Start Circuit (for PWM Control)
This function gradually increases the pulse width of the PWM-OUT pin from a 0% duty cycle at start-up to prevent a
sudden increase in the pulse width that may cause problems such as transient stress on external parts or overshoot of the
secondary-side output voltage.
The soft start time can easily be set with a single external capacitance.
Soft start time tss-pwm is determined by PWM-SS pin connection capacitance Css-pwm and an internal constant, and
can be estimated using the equation shown below.
Soft start time tss-pwm is the time until the PWM-SS pin voltage reaches upper-end voltage 3.2 V of the IC-internal CT
voltage waveform after VREF starts up following UVLO release.
Soft start time tss-pwm when Css-pwm is 3.3 nF is given by the following equation.
Rev.2.00 Jan 30, 2007 page 12 of 23
tss-pwm =
* Iss-pwm: PWM-SS pin source current, 25 µA typ.
V_CT
(internal signal)
PWM-SS
comp. out
(internal signal)
PWM-OUT
≈ 4.2 [ms]
Css-pwm × Vct-H
Iss-pwm
=
33 [nF] × 3.2 [V]
25 [µA]
Figure 2
3.2V
1.6V
V_PWM-SS