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Charging Li-ion batteries in portable apps (Part 1)

Posted: 01 Sep 2010 ?? ?Print Version ?Bookmark and Share

Keywords:Li-ion batteries? portable battery? USB charging?

With consumer demands for fewer cords to power their devices, as well as the desire for flexibility to charge from the computer or an AC outlet, nearly all of the current and future released handheld devices are required to charge from USB sources and AC wall adapters. USB requirements present several challenges for battery charging. The requirement to use the same cable and, therefore, a single input for the USB and AC adapter means that the system must be able to recognize and use both sources.

In this article, we use the bq2407x series of devices to illustrate the features and specifications that simplify system design for charging a Li-ion battery in portable applications. Specifically, we will discuss input current limits, quiescent currents, input voltage dynamic power management (VIN-DPM), and the impact of the Chinese charger specification. These features simplify charger design for portable applications.

The most recognized USB specification is the current consumption of the USB device. USB sources are divided into low- and high-power sources. Low-power sources are defined as USB hubs that are not self-powered. These devices use the 500mA from the USB source and must share the current between all of the devices connected to the hub. Low-power sources provide a minimum operating voltage of 4.4V with the current limit set to one unit load, which for USB1.x and 2.0 is 100mA. For SuperSpeed USB, the unit load is increased to 150mA.

View the PDF document for more information.

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