Never hunt around for another crystal again, with the Si5351 clock generator breakout from Adafruit! This chip has a precision 25MHz crystal reference and internal PLL and dividers so it can generate just about any frequency, from <8KHz up to 150+ MHz. This chip is available on the original breakout board with three full edge-launch SMA connectors or a PCB in the STEMMA QT form factor, making it easy to interface with.

The Si5351 clock generator is an I2C controller clock generator. It uses the onboard precision clock to drive multiple PLL's and clock dividers using I2C instructions. By setting up the PLL and dividers you can create precise and arbitrary frequencies.

There are three independent outputs, and each one can have a different frequency. Outputs are 3Vpp, either through a breadboard-friendly header or, for RF work, an optional SMA connector. The STEMMA QT version has an SMA connector for output #1 and the non-QT breakout has outputs for all three ports.


There is a 3.3V LDO regulator so it can be powered from 3-5VDC. We also put level shifting circuitry on the I2C lines so you can use this chip safely with 3V or 5V logic.


On the PCB in the STEMMA QT form factor, there are STEMMA QT connectors on either side that are compatible with the SparkFun Qwiic I2C connectors. This allows you to make solderless connections between your development board and the Si5351 or to chain it with a wide range of other sensors and accessories using a compatible cable

This guide was first published on Aug 12, 2014. It was last updated on Nov 08, 2022.

This page (Overview) was last updated on Aug 12, 2014.

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