Si5351 Programmable I2C Clock Generator (Si5351A / Si5351B / Si5351C) Key benefits Flexible multi-clock source: generates up to eight independent clock outputs, each selectable anywhere up to 160 MHz. Ideal when you need multiple, different clock signals from a single device. Precise fractional synthesis: PLL / VCXO + MultiSynth architecture with a high-resolution fractional divider allows non-integer frequencies across a wide range with an error of 0 ppm. Easy integration and control: configurable over I2C for software-driven clock setup, reprogramming, and dynamic frequency changes without hardware swaps. Crystal and oscillator replacement: built-in oscillators and VCXO capability reduce board space and component count by replacing discrete crystals, crystal oscillators, VCXOs, PLLs, and fanout buffers. Core features and performance Frequency range: generates frequencies from 8 kHz to 160 MHz. Outputs: up to eight independent outputs; each output can produce any frequency within the device range. Architecture: PLL/VCXO front end with MultiSynth fractional dividers for high-resolution frequency generation. Interfaces and compatibility: configurable via I2C; suitable for use with crystals, crystal oscillators, VCXOs, PLLs, fanout buffers, and microcontroller/FPGA clock inputs. Model differences (what each variant provides) Si5351A: Produces up to eight free-running clocks using an internal oscillator. Designed to replace multiple crystals and quartz oscillators on a board. Si5351B: Includes an internal VCXO. Offers flexibility to replace both free-running and synchronous oscillators and to serve as an alternative to pullable crystals across a wide tuning range. Si5351C: Provides the same output flexibility as the other variants but synchronizes to an external reference clock (CLKIN) when a system reference is required. Practical use scenarios Embedded systems and FPGAs: Replace multiple discrete crystal oscillators and supply independent clocks to microcontrollers, FPGAs, and peripherals while reducing BOM and board area. Radio and SDR front-ends: Generate accurate, non-integer LO or sampling clocks up to 160 MHz under software control; switch frequencies on demand via I2C. Test, measurement, and clock distribution: Provide multiple, precisely synthesized clock outputs for bench instruments or as a compact fanout buffer replacement. Why choose the Si5351 family Consolidates many discrete clock sources into one programmable chip. Software-configurable via I2C for rapid development and flexible field updates. Covers a broad frequency range with high-resolution fractional synthesis and per-output programmability. Three variants let you choose internal oscillator, internal VCXO, or external clock synchronization to match system reference needs.