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A Charging Downstream Port (CDP) is a USB Battery Charging 1.2 port that can charge a connected device while still supporting USB data communication. Under the BC 1.2 behavior described by Microchip, a compatible portable device can draw up to 1.5 A after detecting the port; that is a standard capability, not a promise about every port marked “charging.”
What “Charging Downstream Port” means
CDP stands for Charging Downstream Port. It is one of the port types defined by USB Battery Charging Specification 1.2 (BC 1.2). The USB-IF’s BC 1.2 document library identifies the specification and its compliance plan.
Unlike a charging-only port, a CDP can provide power and maintain USB data communication. The device detects the charging capability through BC 1.2 signaling on the USB data lines. Microchip’s Battery Charging with USB overview describes CDP charging up to 1.5 A, regardless of the USB host’s ordinary enumeration power limits.
How a CDP differs from other BC 1.2 ports
| BC 1.2 port type | USB data | Charging behavior |
|---|---|---|
| Standard Downstream Port (SDP) | Yes | Standard host or hub port. Available current follows USB configuration and suspend rules. |
| Charging Downstream Port (CDP) | Yes | Supports data and BC 1.2 charging; a compatible portable device may draw up to 1.5 A after detection. |
| Dedicated Charging Port (DCP) | No | Charging-only BC 1.2 port. The USB-IF compliance procedure specifies a shunt of no more than 200 ohms between D+ and D−. |
The port distinctions and charging behavior are explained in Microchip’s BC 1.2 overview. The electrical criteria are from the USB-IF’s Battery Charging compliance updates; they are compliance-test details, not a complete test procedure for every implementation.
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- Read Before You Buy — No Video Output: These adapters support charging and USB 2.0 data transfer, but cannot transmit video signals. Except for standard USB webcams (which use USB data only), they are not compatible with HDMI/DisplayPort cables, video-capable USB-C hubs, or docking stations with video output.
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What the 1.5 A figure does—and does not—tell you
The 1.5 A figure describes the BC 1.2 charging behavior for a compatible device connected to a CDP after detection. It does not establish the charging speed of a particular phone, tablet, cable, or port. A generic “charging” label or connector shape alone does not prove that a port is a CDP or reveal its supported current.
In the USB-IF’s published BC 1.2 compliance procedure, a CDP must maintain at least 4.75 V on VBUS at a 1.5 A load. The same procedure specifies the DCP D+/D− shunt criterion shown above. These values describe that compliance procedure; the page does not state a publication year for the specific test details.
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BC 1.2 detection uses D+ and D−. Microchip notes that the charging mechanism requires those conductors to be present in the cable, so a charge-only cable without data lines may prevent the device from detecting the BC 1.2 charging behavior.
CDP is not the same as USB Power Delivery
CDP is a port category in USB Battery Charging 1.2. USB Power Delivery (USB PD) is a separate power-negotiation specification. USB-IF says USB PD is designed to coexist with standard USB Battery Charging implementations. Its USB Charger (USB Power Delivery) page describes USB PD 3.1 capability of up to 240 W over a full-featured USB Type-C cable and connector. That figure applies to USB PD 3.1, not to a BC 1.2 CDP.
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How to interpret a port description
When a specification says “CDP,” read it as a claim about BC 1.2 support for both charging and data, not as a universal charging-speed guarantee. To assess a real connection, check the device and port documentation for the charging standard and supported output, and use a cable that carries data if you need BC 1.2 detection and USB communication.
Quick Recap
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- 5-in-1 Connectivity: Equipped with a 4K HDMI port, a 5 Gbps USB-C data port, two 5 Gbps USB-A ports, and a USB C 100W PD-IN port. Note: The USB C 100W PD-IN port supports only charging and does not support data transfer devices such as headphones or speakers.
- Powerful Pass-Through Charging: Supports up to 85W pass-through charging so you can power up your laptop while you use the hub. Note: Pass-through charging requires a charger (not included). Note: To achieve full power for iPad, we recommend using a 45W wall charger.
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