Beyond being a data interface, one of the best and possibly most well used features of the USB interface these days is as a charging standard for a wide range of devices, least not for phones. The USB-IF has already provisioned a couple of USB charging standards under the USB Battery Charging specification which is currently at versions 1.2, but is now looking at providing something a with a little bit more power.
Weäre not quite sure how the new "power delivery standard" is going to be implemented and as yet it doesnät have a name. Itäs said to be able to co-exist with the current USB Battery Charging standards for both USB 2.0 and USB 3.0, although weäre no longer looking at a mere 2.5 to 4.5W, instead weäre talking 100W. Thatäs quite a jump, especially considering that the USB-IF is saying that the new standard will be compatible with all current cables and connectors.
If you have any kind of background in electronics or electrical engineering youäll most likely have noticed that there are some issues here. Cables normally have various AWG (American Wire Gauge) ratings on them which contain the specifications of the cable itself. The best AWG rating we found on some USB cables we had lying around was AWG24 which is fairly thin cables and they are limited to about 3.5A. On top of that the cables are rated at 30V and adding things up we end up with 105W. The USB-IF obviously cutting things very close here with a 100W standard as the cables in question were high-quality USB cables and not necessarily representative if the kind of cables everyoneäs using.
One of the nice features of the new power delivery standard is that the Voltage and current draw of the connected device will be auto negotiated. What this means is that whatever device you plug in thatäs compatible with the standard will tell the power source that it needs xV and yA and the power source will then respond either by delivering the requested power, or if it canät deliver the requested power it should still be possible for the device to trickle charge.
Intel was penning on something similar during IDF last year, but at the time Intel suggested a 35W specification at 42V/1.8A, with the possibility of reaching 200-300W in the future by using new connectors and cables. That said, the USB-IF standard seems more sensible even if itäs dangerously close to the cable specifications and this really has to be pointed out, as if youäre using sub-par cables and start putting too much power through them, they will literally melt because they canät handle the current.
Weäll have to see how things play out, but itäs an interesting development, especially as USB has already become a predominant standard for charging a wealth of gadgets from. The standard should be reviewed in Q4 this year by the industry in general and the USB-IF is expecting it to be ratified by early 2012, although donät expect to see any products until much later next year.
Source: USB-IF (PDF link)
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