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I'd like to complete an electronics project by allowing it to be powered over USB-C. The specification is complex, I'd love some help understanding it!

I'll need to draw ~ 250mA at 5V for my project (though if there's an appreciable difference for drawing up to 1.5A I'd be interested to hear about it); assuming I have a dumb USB-C socket, what circuit should I build to:

  1. Provide 5V, ~250mA for my project
  2. Suitably protect the power source from issues with my project

Thanks!

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  • \$\begingroup\$ Most of what is in that document (which is NOT a proper specification but more a "quick guide" of what's possible, a proper technical specification would be 10x longer and much more technical) does not apply if you need 5V, 250 mA. In my understanding there's nothing special you need to do, that 5 V is already available by default (but someone who knows better, please correct me). Also not seeing why you would need USB-C because what you want can easily be done using a microUSB socket. \$\endgroup\$ Sep 6, 2017 at 7:53
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    \$\begingroup\$ AFAIK you can draw at least 1.5A @ 5V from a USB-C without negotiation. Moreover, USB-C ports shall gracefully handle attempts to draw up to 3A, shutting down or drooping the voltage if they cannot provide the current that the device attempts to draw. \$\endgroup\$ Sep 6, 2017 at 8:48

1 Answer 1

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If you are building a project (device) with "dumb Type-C" port and want it to get powered from a USB host with Type-C port, you need to do the following:

  1. Use a "full-featured" Type-C to Type-C cable. The cables can be for USB2 only (which is hard to find), or a standard C-C cable with all USB 3.1 wires (which you will not use, so this would be some waste). The important thing with the C-C cable is the presence of CC wire between two ends of a cable, and, of course, GROUND wires, and VBUS wires.

  2. Your device must have two 5.1k pull-downs on both CC pins of your connector. Without these resistors the Type-C port won't deliver any power.

  3. Your USB Type-C host (or charger) will have a pull-up resistor on its CC pins. The value of resistor will indicate the port's power capability

Pull-up to 5V port capability

56 kOhm => 500 or 900 mA

22 kOhm => 1.5 A

10 kOhm => 3.0 A

  1. If you need only 250 mA from the power source, you can just take it, up to 500 mA, and do nothing;

  2. If you really need more than 500 mA, your device/project must check the voltage level on one of CC pin (whichever is active), to verify host power capability.

    • If the level is below 420 mV (+-20%), you shouldn't take more than 500 mA, the port can't supply more than that, and will likely drop off the VBUS; this level would correspond to 56k : 5.1k voltage divider;

    • If you sense the CC level as 940 mV +- 8%, you can take 1.5 A, from the cable. This level will come from 22k pull-up, if the host port supports 1.5 A current;

    • If you sense more than 1.7 V (+-8%), or 10 k pull-up on host side, you can take up to 3.0 A with no problem.

You can design this three-level comparator (and related logic) by yourself, or you can use any IC offered for this specific purpose by Texas Instruments, Maxim, Cypress, NXP, STMicro, etc.

Keep in mind that a typical Type-C receptacle needs a thin PCB (0.8 mm), which is fairly inconvenient for DIY projects. Alternatively there are vertical-mount Type-C receptacles that can go to any PCB, just they have the same small 0.5mm pitch which is challenging to solder.

If you are making a device/project with standard Type-B receptacle (or uB), you just need to use proper legacy cable, and do nothing. But you should restrict your power consumption to 500 mA.

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    \$\begingroup\$ This is an outstandingly comprehensive and concise answer - absolutely perfect. Thank you! 🙇 \$\endgroup\$
    – JP.
    Sep 8, 2017 at 7:14
  • \$\begingroup\$ Thanks for the great answer! Do you know what the search term is for the kind of IC you mention? I find a lot of different ICs, but they are for charging, for USB PD (I only need "simple" USB power sensing), for using USB with data, etc.. \$\endgroup\$
    – jdm
    Mar 30, 2018 at 8:11
  • \$\begingroup\$ @jdm, Google for "USB Type-C controller" -"power delivery" if you need only basic CC functionality, and not PD. \$\endgroup\$ Mar 30, 2018 at 17:07
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    \$\begingroup\$ Note that there are also power-only right-angle surface mount USB C receptables, e.g. the CUI UJC-HP-3-SMT-TR. In contrast to a full-featured 24pin receptable, it only has 6 pins. Much easier to handle for hobbyist applications. \$\endgroup\$ Jun 6, 2020 at 23:11
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    \$\begingroup\$ @KeeganJay, technically it is all documented in USB Type-C connector specifications. You only need to translate the table data into a user algorithm. usb.org/sites/default/files/… \$\endgroup\$ Aug 9, 2022 at 6:04

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