USB Charging


In the modern world of portable electronic devices, USB (Universal Serial Bus) has become the ubiquitous standard for power delivery and charging. The evolution of USB has been remarkable, rapidly advancing to support higher wattages and faster charging capabilities. Understanding the intricacies of USB power delivery is crucial for both consumers and system design engineers. 


USB Power Delivery System

In the USB power delivery system, two essential roles come into play: the power source and the power sink.

Dual Role Port (DRP)

Type of USB Charging

Passive Charger

Passive USB chargers detect and identify the correct power source type by monitoring the positive (D+) and negative (D-) terminals of the USB data line. This method is commonly used with USB Type A interconnects.

USB Power Specifications:

USB Power Source Types:

Charging Downstream Port (CDP): An extension with USB 2.0/3.0 current limits allowing up to 1.5A output current, associated with USB host ports on computers or hubs. 

Active Charger

Active USB chargers take a more advanced approach, using digital communication for power negotiation and establishing power delivery with the source device. 

Note: In USB Type C interconnect, channel configuration (CC) pin are used for power communication.

Example Implementation

Summary and Conclusion:

USB charging has become the de facto standard for powering and charging portable and low-power electronic devices. Understanding the different USB charger types, their capabilities, and how they interact with devices is essential for both consumers and system design engineers. Whether you're selecting a charger for your smartphone or designing power delivery for a new product, having a grasp of USB charging protocols is fundamental. 

Further Reading

For those eager to dive deeper into USB charging, the following resources offer valuable insights and information: