Si5351A/B/C

6. Design Considerations

The Si5351 is a self-contained clock generator that requires very few external components. The following general guidelines are recommended to ensure optimum performance. Refer to “AN554: Si5350/51 PCB Layout Guide” for additional layout recommendations.

6.1. Power Supply Decoupling/Filtering

The Si5351 has built-in power supply filtering circuitry and extensive internal Low Drop Out (LDO) voltage regulators to help minimize the number of external bypass components. All that is recommended is one 0.1 µF decoupling capacitor per power supply pin. This capacitor should be mounted as close to the VDD and VDDOx pins as possible without using vias.

6.2. Power Supply Sequencing

The VDD and VDDOx (i.e., VDDO0, VDDO1, VDDO2, VDDO3) power supply pins have been separated to allow flexibility in output signal levels. If a minimum output-to-output skew is important, then all VDDOx must be applied before VDD. Unused VDDOx pins should be tied to VDD.

6.3. External Crystal

The external crystal should be mounted as close to the pins as possible using short PCB traces. The XA and XB traces should be kept away from other high-speed signal traces. See “AN551: Crystal Selection Guide” for more details.

6.4. External Crystal Load Capacitors

The Si5351 provides the option of using internal and external crystal load capacitors. If internal load capacitance is insufficient, capacitors of value < 2 pF may be used to increased equivalent load capacitance. If external load capacitors are used, they should be placed as close to the XA/XB pads as possible. See AN554 for more details.

6.5. Unused Pins

Unused voltage control pin should be tied to GND. Unused CLKIN pin should be tied to GND.

Unused XA/XB pins should be left floating. Refer to "5.6. Replacing a Crystal with a Clock" on page 20 when using XA as a clock input pin.

Unused output pins (CLK0–CLK7) should be left floating. Unused VDDOx pins should be tied to VDD.

Preliminary Rev. 0.95

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Silicon Laboratories SI5351A/B/C specifications Design Considerations
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SI5351A/B/C specifications

Silicon Laboratories SI5351A/B/C is a versatile, low-power clock generator and frequency synthesizer that has gained widespread popularity in various applications, including telecommunications, consumer electronics, and industrial control systems. These devices are primarily designed to provide precise clock frequency generation with low phase noise and jitter, making them ideal for high-performance applications.

One of the standout features of the SI5351 is its ability to generate multiple output frequencies simultaneously. Capable of producing up to three independent programmable outputs, the SI5351A/B/C can generate frequencies ranging from 8 kHz to 160 MHz. With its integrated phase-locked loop (PLL) technology, it achieves excellent frequency stability and accuracy, simplifying the design of frequency-dependent systems.

The device operates under a supply voltage range of 1.8V to 3.6V, allowing it to be used in battery-powered applications without excessive power consumption. The SI5351’s low current draw, typically as low as 25 mA, is especially beneficial in portable devices, extending battery life and enhancing overall efficiency. Furthermore, it features a programmable output driver, which can be set to various drive strengths, ensuring compatibility with a wide array of load requirements.

Configuration and control of the SI5351 are user-friendly, implemented via an I2C interface. This allows for straightforward integration into microcontroller-based designs. Moreover, the device includes an on-chip memory that stores settings, which streamlines the reconfiguration process when power cycling, minimizing setup time for developers.

Another significant advantage of the SI5351A/B/C is its output jitter performance, which is typically below 1 ps, resulting in clean output signals essential for high-speed data communications and precise timing applications. The SI5351’s integration of multiple synthesizer stages contributes to its impressive phase noise characteristics, making it suitable for demanding RF applications.

Additionally, the SI5351 devices offer programmable frequency stepping, allowing users to define custom frequency increments, which is particularly useful in applications requiring precise tuning or modulation. This flexibility, combined with its compact size and simple interface, makes the SI5351A/B/C an ideal choice for engineers seeking a reliable, cost-effective solution for generating clock signals in a myriad of electronic systems.

In summary, Silicon Laboratories SI5351A/B/C provides a robust, low-power solution for high-precision clock generation, characterized by its programmable outputs, low jitter, easy configurability, and broad frequency range, making it an excellent choice for both commercial and industrial applications across various sectors.
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