Universal Serial Bus (USB) is an industry standard developed that defines the cables, connectors and communications protocols used in a bus for connection, communication, and power supply between electronic devices.
In many portable products, USB is often used both as a communication port and as a power delivery port to accommodate battery charging. For example, a standard USB 2.0 compliant port may provide a maximum power delivery of 7.5 W (5V at 1.5 A) to a dedicated charging port that may be used to recharge the battery of a portable device. However, as the battery capacities of portable devices are increasing, for example, from 5600 mAh to 8000 mAh and 10000 mAh, the charging time for these devices increases accordingly. For example, using a standard USB 2.0 compliant port, it takes about 2 hours and 40 minutes to recharge a 5600 mAh battery, but it takes 4 hours and 45 minutes to recharge a 10000 mAh.
Faster charging times may be achieved by increasing the charging current and/or charging voltage. USB Power Delivery (PD) specification specifies using certified PD aware USB cables with standard USB type A/B connectors to deliver up to 100 W of power at 20 V. USB PD requires the use of PD-aware cables. For example, PD-aware cables with USB-micro B/AB connectors may support a maximum power of up to 60 W at 20 V, 36 W at 12 V and 10 W at 5 V. Consequently, under new USB standards, currents up to 5 A and power up to 100 W may be transferred through power delivery aware cables.
USB specification requires specification on the electrical parameters for the USB cables. For example, USB specification requires that USB cables have an American Wire Gauge (AWG) rating of 24-26, and further require that micro-B connectors have less than 50 mΩs.
However, USB cables including PD-aware cables may not be able to safely handle the large currents. For example, the cables may become defective during use due to field stress. Additionally, some of the USB manufacturers may not have good quality control. The large power supplied through a defective USB can pose a significant safety risk. Similarly, due to backward compatibility, end users may not be aware of the necessity to use the newer PD-aware cables.