Switching USB Power Manager with PowerPath Control Offers Fastest Charge Time with Lowest Heat:Lithium-Ion and Lithium Polymer batteries are common
in portable consumer products because of their relatively
high energy density—they provide more capacity than
other available chemistries within given size and weight
constraints. USB battery charging is also becoming
commonplace, as many portable devices require frequent
interfacing with a PC for data transfer.
As portable products become more complex, the need for
higher capacity batteries increases, with a corresponding
need for more advanced battery chargers. Larger batteries
require either higher charging current or additional time
to charge to their full capacity. Most consumers look for
shorter charge times, so increasing the charge current
seems obviously preferable, but increasing charge current
presents two major problems. First, with a linear charger,
increased current creates additional power dissipation
(i.e., heat). Second, the charger must limit the current
drawn from the 5V USB bus to either 100mA (500mW)
or 500mA (2.5W) depending on the mode that the host controller has negotiated.