55 MHz fixed-frequency clock — MEMS resonator, not quartz
The DSC1121CI2-055.0000T is a 55 MHz fixed-frequency XO built around a MEMS resonator rather than a quartz crystal — the MEMS die is sealed at wafer level, which eliminates the quartz start-up uncertainty and reduces sensitivity to board-level vibration and shock. The Enable/Disable function (pin 1 on the 6-VDFN package) lets the system gate the clock for power savings — when disabled the supply current drops to 22 mA max, enough to keep the internal bias alive but stop the output.
The 2.25V to 3.6V supply range spans both 2.5V and 3.3V logic rails without a separate regulator — a single DSC1121CI2-055.0000T serves a mixed-voltage board where the FPGA core runs 2.5V and the I/O bank runs 3.3V.