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AP63203WU Step down IC keeps burning down.

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AmeliaBuns:
Hi! I have been designing a filament drier PCB and it's one of my first projects.
Everything on this board works great when connected via SWD or when I inject 3v on the line (except my clumsy stupid brain wiring I2C to PA6 PA7 instead of  PB6 PB7....)
The problem is, when I connect the board to 12v, the power LED flickers, and the 3.3v is at 2.2v peak with 1v of noise with a frequency of 700hz~ which is really strange. After bumping the voltage to 24v, the IC just got busted and yeah.... now it's practically a short. The load on the step-down was only 50ma~.

Does anyone here have an idea of what could be wrong? Thanks! (also yes I know the design is awful, I got really tired of messing with it and I'm a beginner so I figured, as long as it's wired correctly xD)

I also put a very poor photo of what my scope saw, sorry I had to hold the board with my hands and inject the power so I only have this awful photo before my board went permanently kapoom!

EDIT: General To-do for V3 of this board:
- Fix i2c.
- move fuse to be after the capacitor
- move inductor and caps close to IC by rotating.
- Remove Fuse
 - Change caps to 0805 and better ratings (Voltage etc) (appearntly ratings on Caps are not that great or detailed, it might not be 22uf at 3.3v dependign on the rating!)
 - Change inductor, it's overkill for 1mhz and my current, the value can be changed too.

The Doktor:
I think that part of your problem is that there is a fairly long path from the output capacitors back to the input ground. I am rather new to switching power supplies, but here is a board I laid out using precisely that regulator. Note that I tried to keep all loops as short as possible, as I have seen others recommend.

Also, what is the purpose of the fuse? In my use, the maximum load is only about 100 mA, but I do believe this chip is capable of protecting itself during an overload. BTW, what value inductor did you use?

AmeliaBuns:
4.7uH! and tbh I only realized that the IC has built-in protection after adding the fuse!
Also, I doubt a path that's slightly long would cause SUCH a drastic failure and killing 2 AP63203WU ICs
Your design is much better, but My confusion is why the issues are THIS drastic, because Worst case scnario on my design is just poor ripple performance as far as I understand.

The Doktor:
I would tend to agree with you that that does not look all that extremely bad, but do remember that the chip switches at 1.1 MHz.

While we wait to see if anybody more experienced in switching power supplies chimes in, I will tell you one thing I would've tried in your situation. It is a very simple, very low skill thing to do, but if you remove the damaged regulator and supply 3V3 from a separate power supply, Does the rest of the circuit work as predicted? It should be simple to test, on your design the regulator is completely disconnected by removing the fuse. Also, before you blew it up, did you see what the regulator does with no load?

Regardless, I still consider you lucky. Anytime I destroyed a component, it always seems to be expensive or I don't have another one laying about, oftentimes both. Seriously, don't feel bad, you say you are a beginner. Part of learning is making mistakes. With perseverance and advice from those more experienced than yourself, you will ultimately be successful.

AmeliaBuns:
It does! although I tested this before burning the step down, I'll try again after i'm home with the IC removed.. And you're right, I forgot about the switching frequency, such a high freqency as far as I understand means you have to be careful.
My fear is that I'll wait a month and waste yet another 5 precious PCBs that I have to throw out, So i'll wait a bit longer, otherwise I'll do what you said. Maybe even design the step down as a seperate PCB to plug/solder into this one (Like an ESP32 module)

And thank you, you're very sweet! I am a bit down but I won't give up! Third time's the charm :)

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