There’s a whole set of USB charging specs you’ve probably never heard of because big-battery smartphones, tablets and 2:1’s demand shorter charge times.
Editor’s note: this particular blog posting is sponsored by Pericom Semiconductor.
Now that you can buy $5 USB chargers everywhere (mains- and cigarette lighter-powered), it’s tempting to think of them like LED flashlights: cheap commodity throw-aways. And you would’ve been right…until now.
My recent purchase of an Asus T100 Transformer Windows 8.1/Intel Atom 2:1 tablet hybrid forced me to dig into USB charging (Figure).
This device is fabulous with its convenient micro USB charging port with OTG support. No bulky wall wart to lug around. But it refuses to charge normally from any charger+cable except for the (too short) one that came with it.
My plethora of USB chargers, adapters, powered hubs and more will only trickle charge the T100 and take tens of hours. And it’s not just the device’s 2.0A current requirement, either. There’s something more going on.
Just Say “Charge it!”
The USB Innovators Forum (USB-IF) has a whole power delivery strategy with goals as shown below. Simply stated, USB is now flexible enough to provide the right amount of power to either end of the USB cable.
There’s even a USB Battery Charging (UBC) compliance specification called “BC1.2” to make sure devices follow the rules. Some of the new power profiles are shown below:
The reason for UBC is that newer devices like Apple’s iPad, Samsung’s Galaxy S5 and Galaxy Tab devices–and quite possibly my Asus T100 2:1–consume more current and sometimes have the ability to source power to the host device. UBC flexibly delivers the right amount of power and can avoid charger waste.
Communications protocols between the battery’s MCU and the charger’s MCU know how to properly charge a 3000mAh to 10,000mAh battery. Battery chemistry matters, too. As does watching out for heat and thermal runaway; some USB charger ICs take these factors into account.
Apple, ever the trend-setter (and master of bespoke specifications) created their own proprietary fast charging profiles called Apple 1A, 2A and now 2.4A. The Chinese telecom industry has created their own called YD/T1591-2009. Other suppliers of high-volume devices have or are working on bespoke charging profiles.
Fast, proper rate charging from Apple, Samsung and others is essential as harried consumers increasingly rely on mobile devices more than laptops. Refer to my complaint above RE: my Asus T100.
Who has time to wait overnight?!
USB Devices Available
Pericom Semiconductor, who is sponsoring this particular blog posting, has been an innovator in USB charging devices since 2007. With a growing assurance list of charge-compatible consumer products, the company has a broad portfolio of USB ICs.
Take the automotive-grade PI5USB8000Q, for instance. Designed for the digital car, this fast charger supports all of the USB-IF BC modes per BC1.2, Apple 1A and 2A, and the Chinese telecom standard. The IC powers down when there’s no load to save the car’s own battery, and can automatically detect the communication language to enable the proper charging profile (Figure). Pretty cool, eh?
As For My Asus 2:1?
Sadly, I can’t figure out how the T100 “talks” with its charger, or if there’s something special about its micro USB cable. So I’m stuck.
But if you’re designing a USB charger, a USB device, or just powering one, Pericom’s got you covered. That’s a secret to get all charged up about.