The device contains a D+/D– based input source detection to set the input current limit when a 5-V adapter is plugged-in. The D+/D– detection includes standard USB BC1.2 and non-standard adapters. When an input source is plugged in, the device starts standard USB BC1.2 detection. The USB BC1.2 is capable of identifying Standard Downstream Port (SDP), Charging Downstream Port (CDP) and Dedicated Charging Port (DCP). The non-standard detection is used to distinguish vendor specific adapters (Apple and Samsung) based on their unique dividers on the D+/D– pins. If an adapter is detected as DCP, the input current limit is set at 2.4-A. If an adapter is detected as unknown, the input current limit is set by ILIM pin .

The D+/D– automatically runs when adapter plugs in. The D+/D– detection contains three steps, DCD (Data Contact Detection), primary detection, and secondary detection.

DCD (Data Contact Detection) uses a current source to detect when the D+/D– pins have made contact during an attach event. The protocol for data contact detect is as follows:

• Detect VBUS present and VBUS_GD (pass poor source detection)
• Turn on D+ I_{DP_SRC} and the D– pull-down resistor R_{DM_DWN} for 13 ms
• If the USB connector is properly attached, the D+ line goes from HIGH to LOW, wait up to 0.5 sec. When the DCD timer of 0.5 sec is expired, the non-standard adapter detection is applied to set the input current limit.
• Turn off I_{DP_SRC} and disconnect R_{DM_DWN}

The primary detection is used to distinguish between USB host (Standard Down Stream Port, or SDP) and different type of charging ports (Charging Down Stream Port, or CDP, and Dedicated Charging Port, or DCP). The protocol for primary detection is as follows:

• Turn on V_{DP_SRC} on D+ and I_{DM_Sink} on D– for 40 ms
• If portable device is attached to a USB host (SDP), the D– is below V_{REF_DAT}. Otherwise, it is attached to either CDP or DCP.
• Turn off V_{DP_SRC} and I_{DM_Sink}

The secondary detection is used to distinguish two types of charging ports (CDP and DCP). The protocol for secondary detection is as follows:

• Turn on V_{DM_SRC} on D- and I_{DP_Sink} on D+ for 40 ms
• If portable device is attached to a Charging Downstream Port (CDP), the D+ is below V_{DAT_REF}. Otherwise, it is attached to DCP.
• Turn off V_{DM_SRC} and I_{DP_Sink}

Most of the time, a CDP requires the portable device (such as smart phone, tablet) to send back an enumeration within 2.5 seconds of CDP plug-in. Otherwise, the port will power cycle back to SDP even the D+/D– detection indicates CDP.