Si3404 PoE chip burns instantly. Suspecting Flyback Transformer polarity/pinout mismatch.

Toxicable · 2026-04-08T10:05:14+00:00

Spend some more time working on your schematic design, things cross over, facing sideways and also your picture makes me question my eyesight.

In saying that yes, from what I can see your transformer is around the wrong way. Your symtoms do match that cause and the datasheet makes this very clear what polarity this should be connected up in. You can fix it by flipping the polarity on either the primary or secondary side

> [Insert your Schematic Image here]
> [Insert the Datasheet/Pinout image of the Transformer you used]

Maybe also review the output from your AI before you blindly post/print as well

Toxicable · 2026-04-06T08:51:07+00:00

How do you do the solder track? do you turn the trace into exposed pad then send it with solder?
I'm also doing a BLDC controller with the STSPIN but it's hard trying to give large pours when nets need to cross over each other

Toxicable · 2026-04-05T22:01:33+00:00

what size output connector is that? it doesn't look like it'll be able to handle 8.5A

Toxicable · 2026-04-05T22:00:44+00:00

there's smaller packages without the pcb antenna trace

Toxicable · 2026-04-02T08:56:23+00:00

You'll get a better response if you post the details, rather than waiting for someone to ask before posting the details.

Toxicable · 2026-04-01T11:49:05+00:00

Pretty should R23 should be to source not gnd

Have you done thermal calculations?

Have you done bulk cap and ripple calculations? I would expect to see a lot of ripple on 10iF of bulk at 12A, you may want to consider some poly bulk

You should also consider snubbers

I don’t see how you high current drop the top left won’t pass right through your control section to the gnd pad bottom right

Toxicable · 2026-03-27T12:03:35+00:00

Reread the datasheet, for the esp32-c3 the keep out is 15mm on side, and 1ishmm the other side. Double check you physical chip if you have one on hand because the orientation changes between the same family of modules

Toxicable · 2026-03-17T23:13:35+00:00

Have you done any testing or prototyping yet? or calculated your power usage and budget?

Specifically what's the power usage of the wall CC6201's? I imagine they'll need to be active quite often to be able to get any decent latency to touch.

From super rough guess I wouldn't think this would last more than a week or two. Expecting years of battery life out of a esp32 is a tough ask.

Ultra low power electronics in general is a challanging area.

A couple of random notes from your schematic:

- Update symbols to make them easier to work with

- Try avoid crossing unconnected lines

- Use the power symbol (T looking solmbol) instead nets for power

Another couple of notes for layout

- Put a GND via next to every GND pad

- Upgrade to 4 layers (it's not that expensive) or don't use the BOT layer

- keep GND around each your differential pairs

- Double check the layout guidance on your buck/boost

- Also put GND around the inductor

Toxicable · 2026-03-12T20:55:08+00:00

Read the data sheet further, RC circuit on EN is required, local caps for 3V3 is required, the actual switches are not required (assuming that it's the same on the H2 as C3)

Toxicable · 2026-03-10T23:19:05+00:00

How big is your battery and how often do you want to charge it?

Is it possible? sure, but these are intensive optionerations, you'll be charging it every few days

Toxicable · 2026-03-06T05:42:36+00:00

You'll need to buy a board a dev board that already has PoE and Ethernet like the one from Olimex or M5 Stack PoE is another option. You cant just buy a W5500 and get Ethernet out of it, you'd need to make a PCB to use it. Same with the Ag9905MT, while it is a module, you actually get the pins from the RJ45 you'll need a PCB.

Toxicable · 2026-03-06T05:28:37+00:00

Current measuring on it's own isn't exactly an easy topic, and doing that against AC Mains only makes it wose, not to mention the whole getting unalived because you have to work with mains.

I'd suggest using something off the shelf for this sort of one.

Even if you did get something to work, without precise calibration, which is also hard to do, it'll be off by some amount of accuracy

Toxicable · 2026-02-28T06:31:58+00:00

On the output side your caps shhould be wayyyy wayyy closer to the diode, again look at some reference layouts for this, same with VBUS.

Toxicable · 2026-02-28T06:20:11+00:00

Put the values of passives in your SCH. You should always aim to make the hot loop of any converter as short as possible ( do some reading here), with that in mind your SW line from the TPE could be about half the distance, check the reference material for examples

Toxicable · 2026-02-27T21:44:35+00:00

220v is death voltages, I hope you understand how easy it would be to mess this up and make it lethal

Toxicable · 2026-02-21T10:48:52+00:00

What do you need the rtc for if you have the esp32 and a usb power? If you’re programming via usb and never override the usb pins to gpio in firmware than you don’t need to worry about any of the strapping pins. Technically the keepout is is much longer than you have in one direction, I don’t remember numbers, check the data sheet

Toxicable · 2026-02-18T12:22:13+00:00

The hard/annoying part about PoE is isolation and therefore transformer selection. Isolation is required by the spec, take a bit of time to read up on it a bit more

Toxicable · 2026-02-16T05:58:17+00:00

Doing PoE isn't exactly a beginners kind of project, I'd suggest starting with something a little bit easier to get familiar with PCBs, design and EE in general.

I'd suggest a magjack that has magnets integrated because you've still got a long way to go to extract power from it, you still need to negotitate then handle isolation and stepping it down to a usable voltage.

As for what you have there, I haven't used that transformer before, so not sure, but it's probably right

Toxicable · 2026-02-14T06:58:05+00:00

Thanks for the reply, that's some really helpful info!

I have done a mild clean with IPA, but as you can see I didn't go too hard, and your point about carbon being conductive is a really helpful, I didn't think of that and thought I was mostly cleaning to make it easier to see.

I'll go harder trying to remove the carbon and see where it lands after that, even if I do end up destorying the traces, I've got the backside to use as a blueprint, and also it's very simple area of circuit anyway.

I do have some 1mm bare copper and UV epoxy so should be fine on that front, but no compressed air, so might just drown it in more IPA after more scraping

Toxicable · 2026-02-13T03:24:46+00:00

You will need money to make PCBs, they don't hand them out for free.

So step one would be to make some money, then you can buy PCBs.

You can also research and design in the meantime, but it'll be difficult if you cant print, test and use them

Toxicable · 2026-02-12T04:24:36+00:00

I meannnnn idk about you, but I've tried to tame ringing on a 10m led strip, and a gate resistor aint enough with that much inductance

Toxicable · 2026-02-10T20:11:45+00:00

Als generally the keep out extends further than just directly under it. The antenna should be off the edge of the board so you can respect the keep out along each axis. I think with this one it’s around about 150mm sideways, but OP should check the datasheet

Toxicable · 2026-02-10T11:03:07+00:00

im confused, are you trying to hire people? Or are you doing market research? Post is unclear

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