NCP1380

[fgsantos7]

Greetings, I'm not new to the forum, but I always used it a lot for consultation, and never to ask for help, guess this my first time for that.

I'm working on a project of a switched power supply based on the on semi's NCP1380B IC.
I've made some design changes and now I feel I'm stuck. I can't get it to work properlly.

In annex you can find my schematic. I'ts very similar to the one found in the development board NCP1380EVB/D.
At this point I think the IC starts badly cause the VCC voltage drops a lot after the first switching sequence.
I'm able to get around 5V in the secondary but if I connect a small load it drops but goes up again in each switching sequence.

The next images were captured all without any load connected to the secondary.



https://www.dropbox.com/s/vfrjvbd576bm1z3/DS1Z_QuickPrint1.png?dl=0
Yellow -> DRV Pin
Light Blue -> VCC Pin


https://www.dropbox.com/s/hqs7u363rc3xfxw/DS1Z_QuickPrint3.png?dl=0
Yellow -> DRV Pin
Light Blue -> VCC Pin
Purple-> Fault Pin
Blue ->FB Pin

MORE IN DETAIL
[img]https://www.dropbox.com/s/ybilizoa1vt4m0d/DS1Z_QuickPrint4.png?dl=0[img]
https://www.dropbox.com/s/ybilizoa1vt4m0d/DS1Z_QuickPrint4.png?dl=0

Does anyone knows how this guy works?
I think the voltage in VCC pin gets too low after switching, but the voltage in Taux is normal and aceptable for the NCP1380