USB Battery Charging (BC) is a USB-IF specification that defines how a USB port and a connected device identify charging capability and handle permitted current. In BC 1.2, a port is classified as a Standard Downstream Port (SDP), Charging Downstream Port (CDP), or Dedicated Charging Port (DCP); those types differ in whether they support USB data and how charging is detected.
What the three BC 1.2 port types mean
BC 1.2 distinguishes ports by their data capability and charging behavior. The current a device actually draws also depends on the applicable USB rules and the device’s own charging controls.
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| Port type | USB data | Charging behavior |
|---|---|---|
| Standard Downstream Port (SDP) | Yes; a conventional USB data port. | Current draw depends on USB enumeration, configuration, and suspend state. It is not governed by a generic fast-charging rating. |
| Charging Downstream Port (CDP) | Yes. | Supports BC charging detection as well as data communication. Microchip describes up to 1.5 A for a device that detects a CDP, subject to applicable requirements and device limits. |
| Dedicated Charging Port (DCP) | No USB data communication. | Designed for charging. The BC 1.2 DCP identification described by Microchip uses a connection between D+ and D−; the maximum shunt impedance is 200 ohms. |
The port identification process checks the USB D+ and D− lines. A detected CDP or DCP can permit a device to draw up to 1.5 A under the described BC 1.2 behavior; that is not a guarantee that every USB port supplies 1.5 A. For the port definitions and detection explanation, see Microchip Developer Help’s Battery Charging with USB and the USB-IF Battery Charging 1.2 materials.
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No. USB Battery Charging, USB Type-C current advertisement, and USB Power Delivery (USB PD) are distinct parts of USB power behavior. USB-IF says USB PD is designed to coexist with standard Battery Charging implementations and directs implementers to the Battery Charging Specification where applicable. See USB-IF’s USB Charger (USB Power Delivery) overview.
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USB-IF’s Type-C compliance update states that its BC 1.2 clarification for USB Type-C chargers took effect in October 2022. The update says those chargers advertise at least 1.5 A of Type-C current and connect D+ to D− with less than 200 ohms. That is a dated compliance statement, not a substitute for checking current USB-IF requirements when designing or evaluating a product. The same page reproduces this Type-C Specification requirement: “A product (Source and/or Sink) with a USB Type-C connector shall only employ signaling methods defined in USB specifications to negotiate power over its USB Type-C connector(s).” The page attributes it to section 4.8.2 and says the associated enforcement took effect in July 2016. See USB-IF’s USB Type-C compliance updates and its Battery Charging compliance updates.
What BC means for charging speed
The label “USB” or the connector’s shape alone does not establish how quickly a device will charge. The result depends on port type, successful protocol detection, device support, cable wiring, and the device’s charging limits. An SDP’s current behavior follows USB configuration and state; a CDP or DCP may support the BC charging behavior described above, but the device still controls what it draws.
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For a general definition, the useful distinction is whether a port is an ordinary data port (SDP), a data port that also supports charging detection (CDP), or a charging-focused port without USB data (DCP). BC 1.2 names these port types; it does not make all USB ports equivalent.
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