The TUSB2514 (U1 in the schematic) operates as a functional interconnect between an upstream connection to a USB host or hub and up to four directly-connected downstream devices or hubs. More devices and hubs can be supported if arranged in tiers. The TUSB2514 can support operation at High-Speed (HS), Full Speed (FS), or Low Speed (LS). In general, the speed of the upstream connection of the TUSB2514EVM limits the downstream connections to that speed (HS and FS) or lower. The TUSB2514 requires a 24MHz low-ESR crystal, Y1 with a 1MΩ feedback resistor. The crystal must be fundamental mode with a load capacitance of 12pF – 24pF and a frequency stability rating of ±100 PPM or better.

To confirm a proper startup oscillation condition, a maximum crystal equivalent series resistance (ESR) of 50Ω is recommended. The TUSB2514 can also use an oscillator or other clock source. When using an external clock source such as an oscillator, the reference clock must have ±100PPM (or better) frequency stability and have less than 50ps absolute peak-to-peak jitter.