Sign in Subscribe

CDP (Charging Downstream Port)

Last updated on 

Introduction

Charging Downstream Port (CDP) is a feature that enables a USB port to act as a power source for charging downstream devices such as smartphones, tablets, and other USB-powered devices. The CDP is a part of the USB Battery Charging Specification (BC1.2), which was developed by the USB Implementers Forum (USB-IF) to standardize the charging of USB devices.

The USB-IF is a non-profit organization that comprises of over 700 companies from various industries that use USB technology. The USB-IF is responsible for developing and promoting the USB standards and specifications, including the USB BC1.2 specification that defines the CDP feature.

In this article, we will discuss the CDP feature in detail, including its benefits, how it works, and its applications.

Benefits of CDP

The CDP feature provides several benefits, including:

  1. Faster Charging: CDP allows the downstream device to draw more power than a regular USB port, enabling it to charge faster.
  2. Compatibility: CDP is compatible with most USB-powered devices, including smartphones, tablets, cameras, and other portable devices.
  3. Standardization: The USB-IF has standardized the CDP feature, ensuring that all USB ports with this feature are compatible with all USB-powered devices that support the BC1.2 specification.
  4. Safety: The CDP feature includes safety mechanisms to protect both the downstream device and the USB port from overcharging, overvoltage, and overcurrent.

How CDP Works

The CDP feature works by enabling a USB port to output a higher charging current than a regular USB port. A regular USB port provides a maximum charging current of 500 mA, while a CDP-enabled port can provide up to 1.5 A or 2.1 A depending on the device.

The charging current is determined by the device's charging circuitry, which communicates with the USB host controller through the USB data lines. The USB host controller can then adjust the charging current based on the device's requirements.

The CDP feature uses the D+ and D- USB data lines to communicate with the downstream device. When a device is connected to a USB port with the CDP feature, it sends a signaling message to the host controller through the D+ and D- lines.

The signaling message informs the host controller that the downstream device is capable of drawing more power and requests that the port provide more current. The host controller then adjusts the charging current to meet the device's requirements, up to the maximum supported by the port.

The CDP feature also includes safety mechanisms to protect both the downstream device and the USB port from overcharging, overvoltage, and overcurrent. These mechanisms include:

  1. Voltage Limiting: The CDP feature limits the voltage output of the USB port to prevent overvoltage and protect the downstream device.
  2. Current Limiting: The CDP feature limits the charging current to prevent overcurrent and protect both the downstream device and the USB port.
  3. Thermal Management: The CDP feature includes temperature sensors that monitor the temperature of the USB port and downstream device to prevent overheating.

Applications of CDP

The CDP feature is used in various applications, including:

  1. Mobile Devices: CDP is widely used in smartphones and tablets, enabling them to charge faster from a USB port.
  2. Portable Devices: CDP is used in portable devices such as cameras, MP3 players, and portable gaming devices to charge them from a USB port.
  3. Automotive: CDP is used in automotive applications to charge smartphones and other USB-powered devices while on the go.
  4. Medical Devices: CDP is used in medical devices to charge them from a USB port, including portable diagnostic devices and patient monitoring systems.

Conclusion

In conclusion, Charging Downstream Port (CDP) is a feature that enables a USB port to act as a power source for charging downstream devices. The CDP feature is part of the USB Battery Charging Specification (BC1.2) developed by the USB Implementers Forum (USB-IF) to standardize the charging of USB devices.

The CDP feature provides several benefits, including faster charging, compatibility, standardization, and safety mechanisms. CDP works by enabling a USB port to output a higher charging current than a regular USB port, and it includes safety mechanisms to protect both the downstream device and the USB port from overcharging, overvoltage, and overcurrent.