An Engineer's Guide to USB Typе-С (2024)
ti.com248 points by gregsadetsky 7 days ago
248 points by gregsadetsky 7 days ago
Bit of self-promotion: I spent the last year or so designing an open-source USB-PD protocol analyzer[1], and the complexity of the protocol can be mind-boggling. Most of the time, the communication between source and sink is really straightforward, but it can get amazingly complicated when both devices are dual-role or come from the same vendor[2].
As messy as it is, however, it's also a very useful protocol that allows even small players to take advantage of the same economies of scale that large companies can take advantage of. Pity that the communication often requires dedicated chips, though thankfully those are relatively inexpensive. I was able to get an RP2350 (the same MCU that's in the Raspberry Pi Pico 2) to interface directly with USB-PD, but they could have made it easier and more accessible.
[1] https://github.com/T76-org/drpd or https://www.crowdsupply.com/t76-org/dr-pd [2] https://hackaday.io/page/399885-a-mac-and-an-ipad-walk-into-...
My new iPhone with USB C charging is such an improvement!
Thank goodness for the European Union. If it weren't for them, we'd all be stuck with these flimsy Apple charging cables forever.
Even if Lightning was possibly a nicer or smaller connector; nothing beats a true industry standard. Makes the entire “what chargers and cables to bring to connect my stuff” question so much easier.
Sadly, that's far from truth...
"back in the day", you had an ericsson charger that fit in an ericsson phone and charget that ericsson phone well... and you had a nokia charger for you nokia that charged your nokia. They physically looked different, they wouldn't fit into any other device, and when you needed a charger, you'd take the one that fit the charging hole and it would charge.
Now, you have a bunch of usb C bricks, some just 5V usb, some USB PD, some QC(2, 3).... then you have a bunch of usb C cables, some with ID chips, some without, some able to carry 15 watts, some 100 watts, and then you have devices, some that can do QC, some that can do smart PD, some with just some resistors, some without even those.
Everything fits in every hole, every charger can take any cable and any device can take the other end of the cable.... but will this particular combo charge your laptop? The cable fits.. will it charge? What about those cheap earbuds that just want 5 volts? The USB-A to usb-C cable that came with them works, but the USB-C to USB-C that you bought after, doesn't. How about that smart LiPo charger, it's USB-C, but it needs at least 9 volts to charge, and not every power brick gives out that voltage. What about charging speed? Will it do fast charge? Your laptop charging light is on, but the battery percentage is going down... why? What about a powerbank, does it charge your laptop? How does it know who does the charging, and who is getting charged?
I mean sure, if you know your standards, you'll know what devices need PD and which ones use QC, you'll read the specs on the power bricks, you know how many watts your laptop needs, how to switch the current directions, which devices can't do proper handshakes, and need usbA->C cables, etc, and you'll get yourself a baggie of a few power bricks and cables for different stuff, but i had to label the cables for my mom, because while everything physically fits, many combinations won't actually charge your device. 10 years ago, this wasn't a problem, since her laptop charger didn't fit her wireless earphones, now it fits and it doesn't charge them.
There were non-apple lightning cables already.
And I have to say, the lightning connector itself is better than the usb-c connect in my opinion. I get that having the pins on the male* plug is a theoretical advantage in durability but that has not been my experience with usb-c connector durability on either end.
EDIT: usb-c has pins on the male plug. Which is what I meant. So female -> male.
> the lightning connector itself is better than the usb-c connect in my opinion. I get that having the pins on the male* plug is a theoretical advantage in durability but that has not been my experience with usb-c connector durability on either end.
I always end up picking a lot of dust out of my usb-c ports on my phones; or otherwise the port wears out and disconnects before charging completes. (Right after my wife entered the hospital in labor, I needed to scrounge around for something to clean out my phone's port because the "go" bag only had a wired charger and my phone wouldn't charge on it.)
It's why I went to a wireless charger for daily use.
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I'm real curious why lightning never became the standard. Was Apple trying to keep it proprietary? Was there a half-hearted attempt to open it up or otherwise convince the Android ecosystem to use it?
> I'm real curious why lightning never became the standard.
Because it is bad. In any connection there are springs that keep the tension, which will eventually wear out. They can either be on the cheap replaceable cable, or in the receptacle that is hardwired into your expensive device.
This is why, in part, USB Mini was replaced by USB Micro. ( https://electronics.stackexchange.com/questions/18552/why-wa... )
> Why Micro types offer better durability? Accomplished by moving leaf-spring from the PCB receptacle to plug, the most-stressed part is now on the cable side of the connection. Inexpensive cable bears most wear instead of the µUSB device.
Definitely had an iPhone where the port was worn out and getting it to connect was difficult.
> I always end up picking a lot of dust out of my usb-c ports on my phones
Lightning has the same issue sadly
I have not used lightning but I have found USB C to be much more fragile than USB A, although better than mini and micro. I would really rather have had evey thing be a few mm bigger and stick with A.
That's fascinating; I've only had positive experience with USB-C cables and terrible with Lightning. What kind of cables do you commonly use?
Couldn't be further from my experience. They would always eventually stop connecting.
I didn't mention the single cable for everything advantage, that goes without saying.
I've also had basically zero issue with Lightning connectors, but had a constant battle with USB-C of every kind to figure out what's charging, what's data, what's PD, and so much more hassle.
I don't get why Apple was forced to colonize by the EU when they had the market-leading connector in place for significantly longer than USB-C even existed.
"It's only USB2!" Does it have to support the faster USB3 speeds? Not really... we don't have to keep forcing everything to include the latest kitchen sink support.
If apple had made lightning an actual standard everyone was using then the eu might have chosen that instead.
But they didn't. Every single other company/device was using usb(c) and it probably wasn't because of some kind if irrational dislike of words starting with the letter L.
It was only 2.5 years between Apple's first device with Lightning (iPhone 5 in September 2012) and their first device with USB-C (12" Macbook in April 2015). It's not like Lightning had a huge track record at that point they just made a decision that they had switched connectors once and didn't want to turn around and do it again. Kind of understandable, but I'm glad to not have Lightning anymore.
Failure to have clear cable capability marking from the start is too bad though, if I needed a high speed USB cable longer than 6" (probably included with a hard drive enclosure or similar) I'm not sure if I own one, and if I do I have no idea which cable it is.
As far as I understand Apple could have still supported an additional lightning port if they really cared about it.
Per gemini for making ligthning accessories you also have to pay 4$ to apple per device that are passed onto the consumer.
I dont know in what way that has to do with colonization.
USB everywhere is nice because you can use the same charger for all kind of devices and dont have to carry multiple with you.
The different kind of specs for usb cables is unfortunate, but you can just buy the highest spec ones and only use them.
Pretty good summary. It can be confusing since type C is "just a connector" but it's pretty heavily coupled with the protocol now.
How can I read out the bit error rate?
Guides like this explain why there are so many broken USB-C devices. The guide mentions that you do not need a PD chip for 5Vs, but then tells you that USB C is a cold connector meaning 0V is on VBUS when nothing is connected and jumps straight into the complexities of the PD protocol running over the CC pins instead of explaining how to get the 5V without the PD chip first.
Then in the section where it tells you how to do that, it fails to properly explain how to connect a load switch (10 cent component at 100 units) to get around the 10uF limit. The vast majority of applications will require less than 15 W and a good chunk of them can't get away with 10uF between VBUS and GND so a schematic how to do it in the lowest cost way would have helped here.
Edit: After reading until the very end I got the impression that this is just an ad for Texas Instruments PD controllers.
Basic 5V devices just need a 5.1k resistor on each CC pin to GND. It is pretty obvious when reading the actual USB-C Connector Specification.
My phone's USB-C port is worn out, and so now it's a brick if I don't have a wireless charging dock around.
Is it physically impossible to get bandwidth and power out of something as durable as a Magsafe connector, even a larger-scale version?
How do you "wear out" a usbc port? Is this phone like 15 years old? My imagination is boggled.
My old Sony xz2c's USB C port wore out after about three years use. About the same length of time they bothered to update Android. :/
I generally stick magnetic USB C connectors into things like keyboards, phones, and iPads.
The slight bulge is worth the reduction in insertions. Also is very convenient for snapping when I need to connect.
Now I want to know, how to add larger than 10uF cap?
Why? 10uF is already pretty beastly, and the point is to dampen signal verses intermittent drops and drains, not power the backing device for any amount of time.
there is a timestamp as parameter, I don't know, what it is good for, but the link works without it as well
Might be for cache busting.
could be, but for pdf documents I would assume that they are not changing this much
TI usually links to chip datasheets, which do tend to change from time to time. Having both a reference to a specific revision and a trivial link to the latest revision is quite handy in practice.
timestamp corresponds to Oct 08 2025, so probably the last time the file was modified
Nice one. I need to read this later.
USB-C reminds me of HTTP: one familiar interface hiding an enormous amount of complexity underneath.
That's great for experts, but difficult for everyone else because the same connector can expose wildly different capabilities depending on the implementation.
The EPR safety design is the part worth highlighting for anyone not deep in USB PD. The handshake is deliberately structured so a single message error can't accidentally push a port into a 100W plus contract, the sink has to actively drive entry into EPR mode and the source verifies cable capability before sourcing anything above 20V. That's a sensible failsafe given how much heat and current you're dealing with at 48V and 5A. The eUSB2 section is also underrated context for why this matters beyond cables. As process nodes shrink below 7nm, the old 3.3V USB 2.0 signaling literally becomes a reliability risk to the silicon itself, which is why chipmakers had to invent a whole lower voltage PHY just to keep USB 2.0 alive on modern nodes.
Not only that, but EPR contracts must be actively maintained in order to remain in effect. The sink needs to send a ping to the source every ~500ms, or the source pops out of EPR mode and forces a renegotiation. This ensures that, if the sink crashes, the source doesn't keep pumping power into a device that can't take it anymore.
Good find!
I use an Apple Silicon Mac and often use programmable keyboards like the Royal Kludge RK61 via USB C. when I press keys such as A, S, D, F, W, or nearby keys in quick succession, the keyboard stops responding completely until I unplug and reconnect it. I've even replaced the USB C cable with a new store bought cable, but the issue still persists.
Check if your keyboard has a way to enable n-key rollover (NKRO)
You are genius! thanks this completely solved my issue, for those curious https://postimg.cc/75hV9tCK
I use usevia, all i had to do was find a keyboard definition file for my keyboard which claude found in 2 minutes!
Usb isn't the issue, you bought an extremely budget mechanical keyboard.
Also avoid Epomaker, had the same issues, but needed a full reflash (every other day), losing all my layers etc. (The import function was broken lol)
turns out it was just me not knowing my keyboard has full qmk support and can be configured via usevia, what N-key rollover (NKRO) is.
my keyboard is actually r65 by royal kludge i got that wrong!
I was gifted this keyboard and i just love its feel.