Understanding Embedded USB2 (eUSB2) and its usage

The need for higher processing power and lower power consumption are driving processors and System on Chip (SoC) to more advanced lower process nodes. For SoCs operating at 1.2V supply that are suitable for mobile phones, tablets, and laptops, using USB2 interfaces is a challenge as it becomes difficult to support 3.3V IO cells. A low voltage USB2.0 solution is therefore required to address the gap.

The embedded USB2 (eUSB2) Physical Layer Supplement to the USB 2.0 Specification was created to address the need for a low voltage, power-efficient USB 2.0 PHY solution. It eliminates the need for 3.3V IO signaling in small process technologies.

eUSB2 can support USB high-speed, full-speed, and low-speed operation, as well as the USB 2.0 L1/L2 link power management requirements. In addition, eUSB2 requires no change to the existing USB 2.0 software programming model. eUSB2 also uses the same two data line configurations, eD+ and eD- as USB2 D+ and D-. Vbus and power delivery are not impacted by eUSB2.

Key eUSB2 PHY features:

• Supports high-speed, full-speed, and low-speed operation
• Supports Single-ended digital low-voltage signaling
• Supports selected single-speed configuration in native mode
• Supports USB2.0 operation based on repeater architecture
• Supports link power management LPM-L1 (L1) and Suspend (L2)
• Supports register access protocol (RAP) for eUSB2 device or repeater configurations
• Fully compliant with USB2.0 base spec at the protocol layer
• No change to USB2.0 software programming model
• Not compatible with the physical layer defined by USB2.0
• Not compatible with standard USB2.0 connectors defined by USB2.0 and its derivatives

eUSB2 has two main operating modes: native mode and repeater mode.

Native Mode

eUSB2 interface can be used to connect two devices on the same board, as shown below in the diagram where the host SoC is connected to the device SoC. This is called native mode. Native mode is a dedicated internal connection between the USB Host and the device.

Repeater Mode

While the native mode solves the challenge of low voltage and low power connection, eUSB2 signaling is not compatible with USB2 signaling and hence is not compatible with external USB ports. This leads to eUSB2 repeater mode. Any SoC that supports eUSB2 can be paired with an eUSB2 repeater to maintain interoperability and backward compatibility with the USB ecosystem of host, hubs, and devices.

In the above topology diagram, we can see that the eUSB2 repeater is a component that translates between eUSB2 signaling and USB2 signaling. eUSB2 repeater can also be of two types, eUSB2 host repeater and eUSB2 peripheral repeater as shown in diagram, to facilitate various device type connectivity.

Cadence has a mature Verification IP solution for the verification of various aspects and topologies of native and repeater modes of eUSB2 design. For more details, you may refer to the Cadence eUSB2 VIP page or you may send an email to support@cadence.com.