According to the USB specification, there are three players in the USB PD / USB-C point-to-point connection system: the power supply device (Source), the powered device (Sink), and the cable.
In each connection, in order to avoid the blind man feeling the elephant, between the devices will be through the cable “information negotiation”, to know the other end of the cable in the end is a cell phone or charger or computer, to determine whether the other side of the power supply or receiving equipment, communication power supply specifications / receiving specifications, data transfer rate specifications and other key information.
As an important bridge between information communication and power transmission, USB-C cables can be equipped with an “E-Marker” chip inside the terminal head to act as a third party in the “information negotiation”.
E-Marker chip is “optional”, no E-Marker chip wire due to security reasons, the current is limited to 3A, to avoid high resistance value of large current overheating security problems; and the use of 3A E-Marker chip wire, the entire fast-charging system maximum current transmission is also 3A; the use of 5A E-Marker chip wire, the entire fast-charging system maximum current transmission is also 3A; the use of 5A E-Marker chip wire, the entire fast-charging system maximum current transmission is also 3A. With 5A E-Marker chip, the maximum current transfer of the whole fast charging system can only reach 5A.
