2 eUSB2 Electrical Specifications

While designing an eUSB2 repeater application has many similarities to a USB 2.0 application, there are some notable differences. Instead of the 3.3-V differential signaling used for USB 2.0 full-speed and low-speed applications, eUSB2 uses 1.2-V or 1.0-V supply voltage (VCC) single-ended signaling. In addition, in eUSB2 high-speed the differential signaling has low swing (200 mV nominal); about half that of USB 2.0 high-speed signaling.

To support the low differential voltage swing, the eUSB2 SoC transmitter and the eUSB2 repeater transmitter (eUSB2 side only) must be source series terminated for good signal integrity. The source impedance mismatch on the eUSB2 transmitter is also limited to 4 Ω to prevent common-mode voltage variation. This mismatch can come from process variation or layout. In addition, an eUSB2 repeater application is required to have its eUSB2 receiver differentially terminated to minimize jitter in the system.

Due to the much lower IO voltage, there are also strict requirements in the eUSB2 Supplement around system power to reduce common-mode noise.

• VCC of two connected eUSB2 applications (SoC and repeater) must be within (15%) of each other at all times.
• GND of two connected eUSB2 applications (SoC and repeater) must be within (4%) of each other at all times.

Another difference from USB 2.0 is that the transmit impedance for eUSB2 is 40 Ω with a differential termination impedance of 80 Ω, instead of the 45-Ω and 90-Ω impedances respectively required by USB 2.0. To enable easier routing on PCBs with both eUSB2 and USB 2.0 traces, the recommended trace differential impedance for a eUSB2 design (native or repeater) is 85 Ω. Table 2-1 and Table 2-1 outline the various eUSB2 and USB 2.0 impedance requirements.