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UCC28780: UCC28780 Doesn't start

Ivan Andelic
Prodigy 70 points
Part Number: UCC28780

Hello,

I am using UCC28780 for my Activ Clamp Zeta-Flyback Converter. The Output Power of the Converter is 160W (40V and 4A) and i already  used your UCC28780 Si SIMPLIS Model (45W Output Power) for my Simplis Simulation and adjusted the circuit parameters with help of your e UCC28780 design calculator for my Topology and Output power. In Simulation everything worked well. Now I built a Hardware and have a Problem that the Controller doesn't  start. The Start Sequence with the SWS, RUN, VDD HVG, works propertly i measured on every pin. The only thing is the main Mosfet Ql (Ql name in your SI Simplis Model) Switch only ones or sometimes  twice and stops until the VDD Capacitor is Empty and a new Start Sequence starts. My Primary inductivity is 75µH and Input voltage for C bulk is 250 V (DC). Can you help me with this Issue?

Thanks!

BR

Ivan

e UCC28780 design calculator

  • 0
    TI__Expert 8210 points

    Ivan

    From your description it sounds like there is a fault even that UCC28780 is detecting that is preventing startup.  Table 2 in section 7.4.10 of the UCC28780 datasheet (page 30) describes all the fault that can prevent startup.  As the "Delay to Action" column shows, there can be several pulses from PWML (drive for Ql in Si SIMPLIS model) before it starts a UVLO reset for VDD.  We recommend to closely measure the behavior and use this table to identify which fault may be causing it to shutdown.  

    I've also attached a debug guide that we have put together for UCC28780.  I recommend reviewing it to see if it can help you identify what is causing your design to not start up.  We will create an application note based on this material that will be available on ti.com shortly.

    UCC28780 Debug Guide.pdf

    Best Regards,

    Eric

  • 0 in reply to Eric Faraci
    Prodigy 70 points

    Hello Eric,
    thank you for your fast response, I will try to solve the Issue with help of debug guide! I will tell you when I solve the Issue.. Thanks!
    Best Regards

    Ivan

  • 0 in reply to Eric Faraci
    Prodigy 70 points

    Hello Eric,

    I solve the Problem, it works now. The Problem was the Current Sense Pin it measured to much Voltage over the Shunt. The reason  was my Layout, on some Points it was not done properly and I had coupling inductance from other conductor tracks.  Thank you very much for your Help!

    Best Regards

    Ivan