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:
1568-1958-ND -Sparkfun USB-C Breakout Board
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.
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.
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