USB Charging and Power Delivery

Originally designed as a data interface with only limited power delivery capabilities, Universal Serial Bus (USB) has become a primary method of powering and charging mobile devices. In this article, we cover the capabilities of the current crop of USB chargers. 1.Default Power The USB 2.0 specification allows Hosts to deliver 5V at 500 mA, for a total power output of 2.5 watts. USB 3.0 and 3.1 allow 5V at 900 mA (4.5W). Certified Hosts and Devices must limit their power delivery and consumption to these "default" power levels. 2.USB Battery Charging Specification The USB Battery Charging Specification allows devices to draw current in excess of the default power limits. The first version of the specification (BC 1.0) was released in 2007, followed by version 1.1 in 2009, and the current, BC 1.2, in 2010. BC 1.2 introduced three types of downstream ports: Standard Downstream Port (SDP) - power is limited to the default power of the applicable USB specification (USB 2.0 or USB 3.x) Dedicated Charging Ports (DCP) - delivers power only (no data) up to 1.5A Charging Downstream Port (CDP) - capable of delivering both data and power up to 1.5A. 3.USB-C® Current Mode USB-C ports without Power Delivery are capable of delivering 5V at 3A for a total of 15 watts. This is sufficient to charge a smartphone in about 30 minutes and a tablet in 2.5 hours.