Simple way to use USB Type-C to get 5V at up to 3A (15W)

Power
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What I’m writing about today is a simple way to get 5V at up to 3A, power supply permitting using the USB Type-C standards for current sinking end devices from just two resistors on the USB-C connector on your end device, otherwise known as Upward Facing Port (UFP)

This communication goes both ways, USB Type-C standards also has a specification standard for the power source, or Downward Facing Port (DFP) using two resistors to tell your end device what amount of current can be sourced, but we’re not really getting into that.

Also USB Power Delivery(PD) has a standard digital handshake devices and their power sources can use to negotiate to raise the power above 5V for higher wattage and current, that’s separate from this and we’re not going to talk about that neither.

What I’m telling you is just slap two 5.1K 1% resistors on both the CC lines tied to ground on the connector of your end device and now you got 5V at up to 3 Amps and let 'er buck.

To illustrate this as an example Sparkfun has a USB-C breakout board that has the two resistors needed to pull up to 3A from the USB-C source power supply, here’s the part and the schematic:

BOB-15100
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1568-1958-ND -Sparkfun USB-C Breakout Board

SPARKFUN USB-C SCHEMATIC
SPARKFUN USB-C SCHEMATIC1301×501 56.4 KB

Just make sure you got a USB-C cable and power source that can handle 15W, unless you’re feeling lucky.

Doing it this way is a little sketchy. You can ask too much of a power source, such as a tablet, laptop or legacy power adapter, especially if you’re using a USB-A Male to USB Type-C legacy adapter cable. Old power supplies/USB Hubs may not have current regulating capabilities so you could get into thermal shutdown cycling of the semiconductors, or possibly burney burney.

Ok, I lied about not getting into the current capabilities of your power source.

Here’s how devices would normally talk to each other to avoid asking too much of a power source and letting the smoke out using resistors in cases where both the DFP and UFP devices follow the USB Type-C specification.

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Image Sources provided by Microchip Application Note: AN1953

Your power source, or DFP has resistor values for Rp. The end device, or UFP has resistor values for Rd. Normally your UFP and DFP would have methods of sensing the CC ports voltage to adapt and act accordingly.

Together they form a voltage divider that would give you the above Rp/Rd Connection voltages, so you could play around with the pull-up resistor values on your UFP for Rd if your circuit needs only 1.5A or 500mA. It should also be noted companies like TI, STMicroelectronics and Cypress have USB Type-C controller solutions that can do all of this for you.

Lower gauge wire and thin circuit board traces can’t handle 3A, so pay attention to what you’re doing inside that circuit. Here’s a 2.5A Fast Blow Fuse, just throwin’ that out there, you know, no reason. Digi-Key PN: F6127CT-ND

Along the lines of being a little sketchy, it’s worth mentioning there are some less than reputable manufacturers out there that have used the USB Type-C standards outside of intended specification.

One thing that is not recommended to ever do is use or build USB-A Male to USB Type-C adapter cables that have the Rd resistor built in to spoof the specification to draw 3A. An engineer over a Google has well documented the results of manufacturers that hack the USB Type-C spec to negative results, sometimes catastrophic.

It would not be advisable to go to market with a device that has the USB Type-C port and a resistor asking for 3A without ability to sense the CC Port voltage and draw less current if needed, especially because of how prevalent legacy adapters are currently in use, but if you built your circuit and know the capabilities of your power source, may your LEDs shine ever brighter and your lithiums charge faster.

If you want to get into USB-C Power Delivery to play around with getting higher voltages and wattages, here’s an development board from Sparkfun that may suit your needs, good to up to 100W.

MFG_DEV-15801
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Sparkfun PN: DEV-15801 featuring STMicroelectronics part STUSB4500

If you want to know more about negotiating power on USB-C through passive methods and higher voltages utilizing the Power Delivery (PD) standard see Digi-Key article Designing In USB Type-C and Using Power Delivery for Rapid Charging

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Dear Kristof, thank you for sharing your knowledge with all us! I am not a pro in the electrical world, but always very much interested in doing some fun little projects! :slight_smile: I have a bit of a problem I thought you might be able to help me to solve. Please would you be able to think of a solution for the following: I have a 5v 2.5A LED Light I want to get powered through a USB C PD battery bank. I tried so many different approaches and the best I can get is the light working pretty stable, but at maximum of 70% brightness. The Power bank is Anker 10k with USB C PD. Bought a cable that goes from USB C to USB A and another cable that goes from USB A to DC 5.5mm that goes straight to the light. First I thought the battery is not good enough, then after reading a bit I started to feel the cable might have some resistors that are reducing the current which in result is not enough for the light. As an example I connected that same cable set I mentioned to my iPhone 11 Pro PD original charger as well as my mac book original charger and the light acts exactly the same as when it is connected to the battery bank. The iPhone charger output is 5v 3amp. This is why started thinking there might be something wrong with the cable. I am lost now! I would really appreciate if you can help me on this! I am more than happy to share some photos with detailed specification of everything. Just let me know if you need it and I will do so. Thank you so much in advance!

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Hello Todjiaa,

Thank you for your inquiry.

I’m not sure what you can expect with your USB-A side, but the USB Type C connector on that battery bank will be able to handle it no problem if you wire up the correct resistor to ground on both of the CC lines, two resistors in total.

If you want to learn a little about the USB-A side and different resistor protocols Benson Leung wrote up something on this subject:

USB Type-C™’s Configuration Channel | by Benson Leung | Medium

If I’m reading his interpretation correctly, for a legacy device adapter with a standard A receptacle you would be required to deploy a 5.1kOhm resistor from CC to Ground.

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Thank you Kristof! Appreciate your help! Will read that! All the best!

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I am not sure that it is inadvisable to incorporate a resistor on a cable for Rp, especially for OEMs who need elevated power levels in their devices. I understand that it’s very important to ensure that the power source which is connected to a cable with certain Rp resistor values for Current advertisement of 1.5A or 3.0A can handle it to prevent risk of fire.

GlobTek offers USB A to C cables on Digikey which advertise
1.5A: product listing Cable Assemblies | USB Cables | DigiKey
3.0A: product listing Cable Assemblies | USB Cables | DigiKey

These USB cables include warnings in the datasheets to ensure proper combinations to power sources and are also physically tagged with a warning and reminder on minimum power source requirements.

A suggestion to OEM users of these cables would be to add an additional tag indicating “This cable is only to be used with xxx device” and can be special ordered through Digikey as such as well.

Perhaps using up valuable system board space is not required in all applications.

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Is there any way to get up to 8A from USB-C? I know that the supply is 65W

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Welcome to the forum.

USB is limited to 3A @ 5V when using the simple resistor method.

You can get up to 100W, 5A @ 20V, by using a special power delivery IC.

https://www.ti.com/interface/usb/type-c-and-power-delivery/overview.html

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Hi, USB Type C connectors are generally not rated for 8A and may overheat or even catch fire in a worst case scenario. So, even though you can try to put it on a conventional 8A power supply, it may fry…it should not be done.

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Thanks. Understood… Then I switch the idea, and I’ll use an external power supply to get 5V @ 8A.

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Cool! Here is a list of GlobTek Power supplies available in stock @ Digikey in 5v 8A: https://r.globtek.info/3vSRBSs

Good luck!!

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Your explanation is a bit off: a Type-C UFP (power sink) always has 5.1kΩ pulldowns on the two CC pins (separate pulldown per CC pin, do not tie them together). The UFP does not get to advertise its current requirements using Type-C negotiation, the DFP (power source) advertises how much you’re allowed to draw from VBUS and you’re required to comply with that. The DFP may also change its current advertisement at any time and you’re required to comply with such changes within 60ms.

The DFP advertises its VBUS current capability by varying the pull-up on its CC pins:

  • 5V 3A capability is advertised by sourcing 330 μA (±8%) into each CC pin (e.g. using 10 kΩ pullup to 5V or 4.7 kΩ pullup to 3.3V)
  • 5V 1.5A capability is advertised by sourcing 180 μA (±8%) into each CC pin (e.g. using 22 kΩ pullup to 5V or 12 kΩ pullup to 3.3V)
  • “Default USB Power” is advertised by sourcing 80 μA (±20%) into CC (e.g. using 56 kΩ pullup to 5V or 36 kΩ pullup to 3.3V)

Default USB Power means:

  • If you connect as USB device then the rules of the applicable USB specification must be followed.
  • If a charger is detected using the D+/D- lines as per the USB Battery Charging 1.2 standard then you may draw up to 1.5 A but the voltage may drop as a result, see that spec for details. This allows for detecting non-Type-C chargers, although Type-C chargers are also still required to support this.
  • Otherwise, you may draw up 500 mA from VBUS.

To determine the current advertised by the DFP you measure the voltage on the CC pin (i.e. across the 5.1kΩ resistor):

  • below 0.20V means no source is connected
  • between 0.20V and 0.66V means you’re limited to Default USB power as described above.
  • between 0.66V and 1.23V means you’re allowed to draw up to 1.5A
  • above 1.23V means you’re allowed to draw up to 3A

Beware that only one of the two CC pins will get pulled up (this is used to detect cable orientation) so you have to monitor both CC pins.

If your device cannot reduce its current consumption below what’s advertised by the DFP then you should simply power off (e.g. using a power switch on VBUS) to avoid overloading the DFP.

Finally, USB Power Delivery (PD) negotiation overrules everything and is the also only way to be allowed to draw more than 3A and/or receive a higher VBUS voltage than 5V.

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What if I use 3.0A cable but the maximum output current from my power bank is only 2.5A. Will it damage the device?

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Good morning, you always want to use a cable rating that’s higher than your actual load. In your example, if your load is 2.5 amps and the cable is 3 amps, then the cable is perfectly suitable. You never want to exceed the cables rating with your load.

I am not completely familiar with your application and how you’re using it, so I cannot guarantee that it works perfectly. However, based on the facts provided, the cable looks perfect.

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What exactly do you mean by a “3.0A cable” ? Every USB-C cable is required to be safe for 3A current.

If however you mean a USB-A(male) or USB-B(female) to USB-C adapter/cable that advertises that the source supports 3A (in violation of the USB Type-C specification), then using this cable means devices will believe that they’re allowed to draw up to 3A, potentially overloading the source if it can’t actually deliver this. This would either result in the source cutting power to the port to protect it, or potentially may result in damage if the source is not adequately protected.

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Your feedback is greatly appreciated. Thank you for this.

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Some more details:

Although the source pulls up both CC1 and CC2, the sink will only see either CC1 or CC2 become high (>0.20V) depending on the orientation of the plug, while the other CC-pin is not-connected or pulled down by the cable. More generally, whichever CC pin has the higher voltage during attachment becomes known simply as “CC”, which is also the pin used for Power Delivery (PD) communication. Brief (<10ms) low pulses on CC should therefore be ignored to ensure you don’t get confused if the source attempts to perform PD communication.

There is an obscure case where a sink will see both CC1 and CC2 high, which is when it is attached as target system to a debug/test system (DTS). Since this “debug accessory mode” of USB-C is inherently device-specific it’s already up to the end-user to avoid connecting an incompatible device to a DTS so you can probably just ignore this case, but ideally you should either consider yourself not-connected in this situation (and draw no power) or abide by the current limits shown below.

The following matrix shows all the info you can get from the CC pins as a sink device:
usb-c-cc-detection

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As a final note: all of the above is still an oversimplification. It should be evident that USB-C is a giant headache and not really something you want to deal with yourself.

If you want a simple way to get 1.5A or 3A from USB-C without blatantly violating the specifications, just use some integrated circuit that handles all of these intricacies for you.

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What if you just want 500mA from USBC?

Do I just add 5k ohm resistors to CC1 and CC2?

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If you don’t monitor the voltage on CC1/CC2 then you must assume the “Default USB Power” rules apply. These are honestly a little bit contradictory, since:

  • If the sink enumerates as USB2 device it must follow the USB2 rules, i.e. max 100 mA until configured (after which it may draw whatever current was declared in the configuration descriptor, up to 500 mA), and max 2.5 mA in suspend;
  • But it also allows a sink to unconditionally draw 500 mA if it is a “USB Type-C Power Sinking Device” (PSD), whch is defined as a “Sink which draws power but has no other USB or Alternate Mode communication function, e.g. a USB-powered light.”

So basically, if a device is too dumb to be able to follow the USB2 rules, the Type-C spec waives those rules and permits 500 mA.

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(The 5.1kΩ pulldowns on CC1 and CC2 are always required, without them you will not get any power on VBUS at all)

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