Sunday, March 5, 2017

USB-C Charging

I've had phones with a USB-C port for a while now. My Pixel C tablet also has a USB-C connector. I thought it was nice, I like the physical connector. It seems more durable than MicroUSB and it's a lot easier to plug in.

I heard about laptops with USB-C and wondered how this would work. Most laptop chargers run a lot more power (watts) and at a higher voltage (19v) than a cell phone charger.

The USB standard supports five power delivery profiles. The specific voltage and current provided are negotiated between the device and the charger. It should be noted that these profiles are not unique to USB-C. When using a MicroUSB connector, a charger can go to Profile 4. Using a USB-A connector a charger can go to Profile 5. But, you will need to full USB 3.x system for this (cable and devices).

ProfileWattsVoltage and Current
1105V @ 2A
2185V @ 2A → 12V @ 1.5A
3365V @ 2A → 12V @ 3A
4605V @ 2A → 20V @ 3A
51005V @ 2A → 20V @ 5A

I recently picked up a Satechi inline USB-C power meter. A fun little device and I recommend it.

When I'm charging my phone (Pixel XL) with a generic USB-C charger I see 5v at about 2a. The current fluctuates a fair bit. I see about the same on my Pixel C and Samsung Chromebook Pro. This is clearly a 10w Profile 1 charger.

When I charging using the adapter that came with my Chromebook Plus I get different results. The phone charges at 9v/2a, as does my Pixel C. When plugged into the Chromebook plus I'm seeing 15v/2a or about 30w. This is a Profile 3 charger, but I don't know about the 15v. Maybe it reports as a Profile 4 and limits the voltage to 15v.

Unfortunately, my Phromebook Plus was fully charged when I took these pictures. But I wanted to show the difference between the generic charger and the Samsung charger.

Generic Charger

Samsung Charger

How do you know which charger to get? How do you know what your device will accept? These are tough questions. I have not seen device manufactures include information about maximum charge voltage and current. I think you can look at the factory charger to see its' power rating (in watts), this will give you a good idea of what's required.

Using a charger that's rated higher than your device will not be a problem. Remember the device and charger negotiate the voltage and current.

Several months ago Google asked phone manufactures to stop using rapid charge systems that are outside the USB spec. This would include Qualcomm's Quick Charge 2.0. Look for USB-C to become more common on phones released during 2017 and beyond.