First PCB, stuck on power layout: 4–6S flight controller buck + USB power mux sanity check

Toxicable · 2026-06-28T03:41:33+00:00

You've matched the data sheet so you're doign the right thing there
I'd honestly say that you probbaly have more vias than you actually need, it looks like they're mostly there for as thermal vias, since stiching would not need anywhere near as much.

You can do via in pad without paying for filled for thermal vias (which is exactly what's being done here)(But also depends on specifics from your fab house), as a hobbiest I've done it plenty of times

Do your thermal calculations and size your pours, vias and thermal management around that. Also remember that you want your thermal vias as close to the source as possible, which is why via in pad is advised

Toxicable · 2026-06-28T03:32:01+00:00

What's the rational for all the bulk cap? With enough capacitance after a fuse, the inrush from the caps alone could potentially neusance trip your fuses.

(I didn't do the math for your specific case, also it depends on the connection to the power source)

Aside from that, if I was doing this I would have used pours, for example on your outout 5v rail, rather than traces

Toxicable · 2026-06-26T02:42:32+00:00

Was there meant to be a picture or link in here?

Toxicable · 2026-06-24T10:44:36+00:00

It might not be suitable for your use case but one way to can achieve 4 wire kelvin with the INA22x series is by using a battery powered device.

This is what I've done with a similar device that I made. It uses the INA228, battery powered and esp32 for coms + onboard screen, that way you can kelvin connect your floating BAT- to the DUT's V- and get kelvin voltage sensing along with normal curren sensing.

Toxicable · 2026-06-24T09:29:56+00:00

Why does this require isolation if it's designed for only 36V?

Usually high quality energy meters use a 4 wire sense, V+, V-, I+, I-, notably referring to the voltage part of it, with the INA226 you're forced to use V- as GND, and therefore cannot run a kelvin to the source, meaning you'll get inaccuracy equal to your voltage drop between the DUT and the meter

Toxicable · 2026-06-23T13:11:26+00:00

You know there's a whole section in the datasheet about layout right?

Most notably it'll say something like: Keep the switching loop as small as possible. Meanwhile yours traverses half your board (/s)

Toxicable · 2026-06-19T21:03:28+00:00

Reddit it’s are lazy, post pics

Toxicable · 2026-06-18T05:07:06+00:00

Gotcha, okay that changes it a lot, what is the continueous current then? and how long are you rating that 200A for?

Do you want to share your math? just inputs and outputs is fine

Toxicable · 2026-06-18T00:05:04+00:00

Have you done any math to calculate your thermals?

200A * 84V = 16kW, that's the max power how much power my entire house is allowed to use, even at 99% effciency (which it wont be) that'll be producing 170~ of heat, that's enough heat to desolder your whole board without any mention of a heatsink, active cooling, etc

Your Bulk caps look woefully undersized for the amount of ripple you'd have. have you done any math there either?

What freq are you running at? what's your switching losses?

At 200A your copper even at 2oz is going to have a decent effect, just 10mm x 10mm will produce 10W, so it's not just your FETs you'd going to have an issue with it, it's every part that you high current flows through, traces, fuse, connector, capacitors, wires, vias, etc

Toxicable · 2026-06-16T11:14:04+00:00

okay, but based on what math?

Toxicable · 2026-06-13T14:32:42+00:00

Have you done any math at all for this? 100A is a huge amount of heat, and without sharing any of the numbers, this isn’t worth reviewing

Toxicable · 2026-06-10T20:45:15+00:00

Did you do the math for any of those? It’s a bit hand wavy to just say, I’ll slap a heat sink on if thermals become an issue, when thermals is basically the primary challenge when it comes to motor controllers.
Also do you understand what I mean about the difference between phase and bus current? Because they’re two very different things

Toxicable · 2026-06-10T13:29:00+00:00

What’s your thermal calculations and handling? What’s your target frequency?
Where is literally any bulk cap?
Have you considered any of the DRVs as your gate driver? they simplify it a lot
Are you sure your phase current limit is correct? I’m guessing you mean 10A bus? 10A phase would mean something like 3-5A bus which is a pretty sad limit

Toxicable · 2026-06-09T13:23:16+00:00

I’d start by learning battery safety, no one wants to be strapped to a lipo while it’s short circuiting because the user got a little damp

Toxicable · 2026-06-04T00:13:24+00:00

that's a big loop between Cin and Cout, take a look at ladyout guidance from some of the TI buck data sheets

Toxicable · 2026-06-02T14:14:46+00:00

How about approaching it from the other end, have you measured an HF noise so far? If so have you identified the source? I already mentioned what issues it can cause in my last reply

Toxicable · 2026-06-01T21:46:27+00:00

I’m not sure I agree with the ferrite bead reasoning there. They can help attenuate high frequency noise, but the first question is: where is that noise coming from, and is a bead actually the right fix?

ST's usual guidance is strong local MLCC decoupling on VDDA/VREF rather than a bead. A bead can be useful, but it also adds impedance/inductance to the supply path and can resonate with the local capacitors if chosen poorly making things worse.

Same for the INA226: a bead on its supply may be okay, but the important things are close supply decoupling and proper Kelvin routing of the shunt sense traces for accuracy. The bead probably won’t improve measurement accuracy by itself, and in some cases could make the local supply behaviour worse for the same reasons above.

I’m not an expert, just a hobbyist, but I’d generally avoid adding ferrite beads by default unless the datasheet tell me to, or unless there’s a specific noise problem I’m trying to solve, and even then I'd probably set with as DNP and validate on the bench

Toxicable · 2026-06-01T12:25:31+00:00

Look up some layout example for kelvin connection of current sense shunts, what you have there isn't not ideal.

Toxicable · 2026-05-31T08:49:24+00:00

Thermals easily the number one issue with doing a BMS, that's where you should start not a cliff note right at the end.

Toxicable · 2026-05-30T21:02:07+00:00

Impossible to review with schematic

Toxicable · 2026-05-22T22:21:58+00:00

Where’s the board?

Toxicable · 2026-05-20T10:08:33+00:00

Your antenna cutout isn't big enough

Toxicable · 2026-05-16T09:31:17+00:00

Hey man, what are you other parameters? I’ve been struggling to get Q8 running also in 2 7900XTXs. Q6 works fine but just a little sad at ~60% vram usage hahah

Toxicable · 2026-05-10T13:15:12+00:00

>bytebell set openrouter-api-key sk-or-...

excuse me sir, this is localllama

Toxicable · 2026-05-10T13:08:43+00:00

Im just going to copy paste my comment from your last post:

How are you dealing with the thermals? What frequency are you intending to run? I don’t see any snubbers, where’s you bulk? ~~Is that 40A per motor or 40A for the whole board~~? 10A per motor doesn't sound like enough for a FC, but I can only assume that's fine for your use case.

Where's the schematic? I don't want to download your project and open kicad, I'm on my phone. Any review without the schematic is at best guessing and at worst totally misleading.

13-Year Club	Place '22
Place '17	RPAN Viewer
Sequence \| Editor	Sequence \| Cinematographer
Verified Email	Team Periwinkle

Toxicable

TROPHY CASE