HA17384SPS Datasheet, PDF (26/29 Pages) Hitachi Semiconductor – High Speed Current Mode PWM Control IC for Switching Power Supply

HA17384SPS/SRP, HA17384HPS/HRP, HA17385HPS/HRP
Notice for Use
OVP Latch Block
• Case
When DC power is applied directly as the power supply of the HA17384H, HA17385H, without using the
transformer backup coil. Also, when high-frequency noise is superimposed on the V_IN pin.
• Problem
The IC may not be turn on in the case of a circuit in which V_IN rises quickly (10 V/100 µs or faster), such as that
shown in figure 15. Also, the OVP latch may operate even though the FB pin is normally at V_OVP or below after the
IC is activated.
• Reason
Because of the IC circuit configuration, the timer latch block operates first.
• Remedy (counter measure)
Take remedial action such as configuring a time constant circuit (R_B, C_B) as shown in figure 16, to keep the V_IN rise
speed below 10 V/100 µs. Also, if there is marked high-frequency noise on the V_IN pin, a noise cancellation
capacitor (C_N) with the best possible high-frequency characteristics (such as a ceramic capacitor) should be inserted
between the V_IN pin and GND, and close to the V_IN pin.
When configuring an IC power supply with an activation resistance and backup winding, such as an AC/DC converter,
the rise of V_IN will normally be around 1 V/100 µs, and there is no risk of this problem occurring, but careful attention
must be paid to high-frequency noise.
Also, this phenomenon is not occuring to the HA17384S, because OVP function is not built-in.
Input
Output
V_IN
V_IN
HA17384
Series
Feedback
GND
Figure 15 Example of Circuit with Fast V_IN Rise Time
Rev.3.00 Jun 15, 2005 page 26 of 28