USB Charging

Introduction

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. 

Background

USB Power Delivery System

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

• Power Source: This is typically associated with the upstream-facing port (UFP).

• Power Sink: Conversely, the downstream-facing port (DFP) is designated as the power sink.

Dual Role Port (DRP)

• USB Type C introduces a game-changer known as the Dual Role Port (DRP). This port can seamlessly switch between UFP and DFP functionalities, making it incredibly versatile. For example, a smartphone can act as a power sink during charging and then become a power source when driving USB headphones..

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.

• • Note: USB Type A D+/D- are configured on each USB power source with a different of resistor network to advertise charger capability

USB Power Specifications:

• USB 1.0: 5V/100mA

• USB 2.0: 5V/500mA

• USB 3.0: 5V/900mA

• BC 1.2 (an extension of USB 3.0): 5V/1.5A

USB Power Source Types:

• • Dedicated Charging Port (DCP): Follows BC 1.2 spec with a maximum output current of 1.5A. Examples include USB wall chargers. 

    • Note: this type of port does not enumerate with a device that connects to it, and it's job is to act as "dedicated" power supply.

    • SDP and CDP  is capable USB enumeration for any devices connected to it, the reason is that  SDP and CDP are host/hub ports found on PC/laptop or USB hub.

  • Standard Charging Port (SDP): Follows USB 2.0 spec with a maximum output of 500mA, typically found in computer USB host ports or hubs. 

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.

• USB Charger Power Delivery (PD) Standard: This follows the USB Charger Power Delivery standard, which coexists with BC 1.2 but is designed primarily for USB Type C devices. It's important to note that not all Type C devices support the USB PD charging protocol. 

• USB PD 2.0/3.0 Power Specifications:

• Supports up to a maximum of 100W (20V/5A).

• Offers multiple voltage and current configurations, including 5V/3A, 9V/3A, 12V/3A, 15V/3A, and 20V/3A.

• Supports programmable power supply (PPS), enabling more efficient charging and reducing charger heat dissipation.

Example Implementation

• Phone Type C Charger (18W):

  • Voltage and Current Configurations: 5V/3A, 9V/3A.

• Laptop Type C Charger (60W):

  • Voltage and Current Configurations: 5V/3A, 9V/3A, 12V/3A, 15V/3A, 20V/3A.

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:

• USB Charging Introduction

• What is Fast Charging?

• USB Charger (USB Power Delivery)