USB on-the-go extends USB power dominance

Tag : usb power supply



Many MP3 players have already bailed on the concept of having aseparate power connection/wall wart combination to charge theirinternal battery pack, and instead use only power from their USBcable, both for operating and battery-recharge power. Relying onUSB power gets rid of wall wart efficiency problems as well asdifferences in international line power standards. The USB powerstandard calls for the host, usually a desktop or laptop computer,to provide 500mA of USB current to power peripherals.
But what about when you want to connect two peripherals -- say, adigital still camera to a cell phone ? Which device provides thepower then?
USB on-the-go (USB OTG) relies on a mini USB connector andbi-directional power. When a non-host device, such as a cell phone,connects to a host, such as a laptop, the cell phone charges fromthe host, and its charger power supply acts as a buck converter tocharge the cell phone battery, dropping the USB 5V down to thelithium ion battery charge voltage of around 3V. When a cell phonecapable of USB OTG connects to another peripheral device via itsmini-USB connection, the cell phone power supply acts as a boostconverter, boosting its battery voltage up to the USB 5V requiredby the other peripheral.
I heard about USB OTG from TI as it prepared to introduce its newbg24150 battery charger, which not coincidentally supportsbi-directional USB OTG power. Here’s a link to the OTG supplement for the USB standard .