INN3670C unstable operation

Hello Zandy,

There are many factors that could be causing this, I will some more details first though.

1. Can you send the schematic and layout of the design as well? The issue may be caused by something here.
2. Can you also clarify what your input voltage range is?
3. Can you clarify what you are seeing in the output voltage? I see that it is not stable but how big is the swing?
4. Was this waveform taken at 2A output current and can you measure the off time between each switching cycle?

As of now, the only suggestion I can give is that we generally do not recommend using premade transformers. A lot of issues can be caused by a transformer that was not properly designed for the application. I recommend using a transformer designed specifically to your specifications but if you can only use a premade transformer, then please run the transformer design through our PI Expert tool to check if the transformer will really work properly in the design.  This includes the number of turns (primary, secondary, bias, etc.), wire gauges, core and bobbin specs, etc. You can find our PI Expert tool here: PI Expert | Power Integrations