Li-Ion Battery Charger ICs offer USB On-the-Go support.

Comprising 4.5 A output, 20 V input-rated switch-mode chargers with I2C interface, bq2419x Series achieves 92% efficiency at 2 A and up to 90% efficiency at 4 A of output current. Fast-charge circuits minimize charge time through battery path impedance compensation, while

[source: http://news.thomasnet.com/fullstory/Li-Ion-Battery-Charger-ICs-offer-USB-On-the-Go-support-20005471]