USB PD and E-Markers Are Key Features

USB PD, where "PD" stands for Power Delivery, was first released in 2012 as a standard to allow charging devices to supply more power than 5 V at 0.9 to 1.5 A. We're not going to go into too much detail on the charging part of USB PD, as it's a separate standard that isn't directly tied to the USB data standards. The part that matters here is that USB PD requires an additional chip that's handling the communication between the charger and device, so the right charging voltage and current can be negotiated. With the introduction of USB4, USB PD will be serving an additional function: It will be used to exchange the capabilities of both hosts and devices. This is required due to the multiple protocols that can now be transferred over USB4, and if the two devices can't exchange the correct information, they'll default back to USB 3.2 and then start a regular USB protocol negotiation.

It might not be the most elegant solution, but it retains backwards compatibility, and as USB PD already has the ability to negotiate between a host of a sort and devices, it became the logical option. Since many USB-C devices are likely to want more than the 7.5 W of power on offer by USB4, it's also logical to allow the power and protocol negotiation to happen at the same time. Due to backwards compatibility, USB4 supports USB PD 2.0 as its baseline spec. There are many companies that make USB PD controllers, although only a few are so far certified for USB4.



USB PD is in and of itself a complex standard, and all USB4 cables are fitted with an e-marker chip. The e-marker chip is part of the USB PD power negotiation and is fitted to cables to make sure they really can deliver the power they're rated for in a safe way. However, with the introduction of USB PD 3.1, the voltage range increased to a maximum of 48 V and an extended power range (EPR) was added to the previous power range which topped out at 20 V, which is now known as the "standard" power range (SPR). USB4 cables will support both SPR and EPR, which means there will be cables rated for up to 60 W, 100 W, and 240 W. So far, it appears that most USB4 cables are rated for at least 100 W.