Another important feature of the HX3 is that it supports both standard power charging mode and accessory charger adapter dock (ACA dock) power charging mode. Standard power charging mode receives V_BUS power from the upstream port to deliver to the downstream ports. When using the ACA dock mode, portable devices can utilize an upstream USB port to charge while functioning as a USB on-the-go host. In this mode, detection starts with the ID pin resistor connection to ground. When the signal becomes active, the V_BUS is open to start charging the upstream port.