I am designing a rechargeable Li-ion cell powered light. I would like for the light to be able to accept a USB input to charge the cell. I would like for the light to run off of the cell when there is no USB source. And I would like to be able to provide power from the cell to a USB device. The light can accommodate 1-4 cells in parallel. I would prefer a cell charge current between 1 and 2 A. Can you recommend an IC which will provide this functionality?