EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: rf-fil on February 26, 2024, 04:24:25 am
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I'm working on something that's being charged by USB-C. I'm debating if I can simply avoid support for 500mA, or even 1.5A devices. My gadget uses a fair bit of power, and if the charger only gave me 500mA, I'd have to manage the internal power consumption in a complicated way.. I'm thinking to disable charging, and signal "wrong charger" to the user somehow, unless I get 3Amp-capable downstream device. (This is easy to detect with the CC lines in USB-C.)
I don't recall ever seeing a USB-C wall plug that is less than 3A. But, I'm not sure about laptops, PCs, etc. My laptop supports 3Amps on its USB-C port, as far as I can tell.
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I feel your pain there. You try to search for the info and all you get is “USB supports charging up to 100 Watts!”
If it helps, MacBooks seem to do 5V 3A
On the too-low-current front, I’d be quite surprised to find anything which was 500 mA only (barring a USB A -> C adaptor cable). In fact, it just might be that the USB C standard requires minimum 1.5A from Power Sourcing Equipment (PSE)…
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The answer is (maybe) in the USB Type-C spec, which is free to download. But not particularly digestible.
The USB Type-C connector uses CC pins for configuration including an ability for a Source to advertise to its
port partner (Sink) the amount of current it shall supply:
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Default is the as-configured for high-power operation current value as defined by the USB
Specification (500 mA for USB 2.0 ports; 900 mA or 1,500 mA for USB 3.2 ports in single-lane or
dual-lane operation, respectively).
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1.5 A.
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3.0 A.
This is defined in "USB Type-C Current" and all USB Type-C sources have to support this. As with many standards writing, it can be a tad confusing. But the very fact a given source is able to advertise the max current it can supply to a sink is IMO an indication that it doesn't have to be able to supply any of the profiles above the default (500 mA or 900 mA). It just has to advertise what it can do.
It's probably very rare though at this point that any USB-C source would not be able to deliver up to 3A, as you noticed. Now for any compliant device, if you do detect it via CC lines as you intend to do, then you'll have no problem. But again, from the phrasing in the standard and common sense given the different levels that are specified, it can be expected than *some* sources may not be able to deliver 3A. The question of how many, good luck finding any answer to that.
One kind of product on which I would *suspect* not necessarily being able to get 3A is typically mobile phones when used as USB sources. Maybe also some smaller tablets. Other than that, a large majority of laptops and USB-C "chargers" should support at least 5V/3A, and many of them also support USB-PD at various levels.