Ever wonder why USB connector’s power are longer than the D+ D- pads? Here’s an app note from Maxim Integrated about these detection proccess and their importance. Link here (PDF)
This application note explains details of the USB Battery Charging Specification 1.2, and the role of charger detection. With the use of charger detection ICs, the USB connector on a portable device becomes a versatile component. The built-in BC1.2 compliance keeps the implementation clean and simple to use.
When designing a compact and portable product, the wealth of features accompanying charger detection ICs make them an extremely attractive integrated circuit.
This is actually a Tutorial, not an App-Note. Maxim-Integrated often (thoughtfully) provides both online and downloadable .PDF documents. Here is a link to the online version mentioned in this post: http://www.maximintegrated.com/en/app-notes/index.mvp/id/5936