Wednesday, May 20, 2015

Updates to USB provide higher power and faster charging

For those who regularly visit our blog here are already aware I do a fair amount of work with regard to test methodologies for optimizing battery life on mobile wireless devices. One directly related topic I have been actively investigating these past few months is the battery charging aspects for these devices. Recharging the battery on these devices takes a considerable amount of time; typically a couple of hours or longer, and it’s only been getting worse. However, there has been a lot of work, activity, and even new product developments that are making dramatic improvements in recharging your devices’ batteries in less time!

The USB port has become the universal connection for providing charging power for mobile devices. When initially available a USB port could provide up to 500 mA for general power for peripheral devices. It was recognized that this was also a convenient source for charging portable devices but that more current was needed. The USB BC (battery charging) standard was established which formalized charging initially for up to 1.5 amps at 5 volts.

This higher charging current and power was alright for mobile devices of a couple of generations ago, but today’s smart phones, tablets, and phablets are using much larger and higher capacity batteries. The end result is, because USB is 5 volts its power thus limited to 7.5W, that it can take several hours to recharge a device’s battery.  This can be very inconvenient if your battery goes dead during the day!

Simply increasing the USB current is not a total answer as this has limitations. First, the micro USB connectors on mobile devices are rated for no more than about 1.8 to 2 amps. To help on this front there is the new USB Type-C cable and connector specification released last year. The new type-C micro connectors are able to handle up to 3 amps and the standard connectors able to handle up to 5 amps. Higher current alone is not quite enough. Also issued last year was the new USB Power Delivery 2.0 specification. This specifies a system capable of providing up to 20 volts and 5 amps. This is more than order of magnitude improvement in power over the existing USB power. Long charging times due to power limitations will become a thing of the past.

The new USB power delivery voltages and currents are a discrete set of levels as shown in table 1. As can be seen the levels depend on the profile/port designation.


Table 1: USB power delivery 2.0 voltage and current levels

The cables and connectors of course need to be able to handle the given level of current and power.  In review of the standard a lot of work and effort has gone into providing this new capability while maintaining compatibility with the past as well. Thus for a new mobile device to take advantage of these higher power levels, it must be capable of negotiating with the charging power port to furnish it. At the same time, if an earlier generation mobile device is connected, it will only be able to get the default USB 5 volt level.

I’m looking forward to seeing this new USB power delivery put into wide-spread use in various innovative new products. Expect to see more about this topic in future posts from me here!

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