Silicon Laboratories SI5351A/B/C Spread Spectrum, Control Pins OEB, Ssen, Output Enable OEB

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Si5351A/B/C

3.4. Spread Spectrum

Spread spectrum can be enabled on any of the clock outputs that use PLLA as its reference. Spread spectrum is useful for reducing electromagnetic interference (EMI). Enabling spread spectrum on an output clock modulates its frequency, which effectively reduces the overall amplitude of its radiated energy. See “AN554: Si5350/51 PCB Layout Guide” for details. Note that spread spectrum is not available on clocks synchronized to PLLB or to the VCXO.

The Si5351 supports several levels of spread spectrum allowing the designer to chose an ideal compromise between system performance and EMI compliance.

Center

Frequency

Amplitude

Reduced

Reduced

Amplitude

Amplitude

and EMI

and EMI

fc

fc

fc

No Spread

Center Spread

Down Spread

Spectrum

 

 

Figure 6. Available Spread Spectrum Profiles

3.5. Control Pins (OEB, SSEN)

The Si5351 offers control pins for enabling/disabling clock outputs and spread spectrum.

3.5.1. Output Enable (OEB)

The output enable pin allows enabling or disabling outputs clocks. Output clocks are enabled when the OEB pin is held low, and disabled when pulled high. When disabled, the output state is configurable as disabled high, disabled low, or disabled in high-impedance.

The output enable control circuitry ensures glitchless operation by starting the output clock cycle on the first leading edge after OEB is pulled low. When OEB is pulled high, the clock is allowed to complete its full clock cycle before going into a disabled state.

3.5.2. Spread Spectrum Enable (SSEN)—Si5351A and Si5351B only

This control pin allows disabling the spread spectrum feature for all outputs that were configured with spread spectrum enabled. Hold SSEN low to disable spread spectrum. The SSEN pin provides a convenient method of evaluating the effect of using spread spectrum clocks during EMI compliance testing.

Preliminary Rev. 0.95

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Contents Functional Block Diagram FeaturesApplications DescriptionSi5351A/B/C Table of Contents DC Characteristics Electrical SpecificationsParameter Symbol Test Condition Min Typ Max Unit Recommended Operating ConditionsInput Clock Characteristics AC CharacteristicsVcxo Specifications Si5351B only Parameter Symbol Test Condition Min Typ Max UnitsParameter Symbol Min Typ Max Unit Output Clock CharacteristicsCrystal Requirements1,2 Thermal Characteristics I2C Specifications SCL,SDA1Parameter Symbol Test Condition Package Value Unit Absolute Maximum Ratings1 Parameter Symbol Test Condition Value UnitBlock Diagrams of 3-Output and 8-Output Si5351A Devices Detailed Block DiagramsBlock Diagrams of Si5351B and Si5351C 8-Output Devices Input Stage Functional DescriptionCrystal Inputs XA, XB Output Stage Synthesis StagesExternal Clock Input Clkin Voltage Control Input VCOutput Enable OEB Control Pins OEB, SsenSpread Spectrum Enable SSEN-Si5351A and Si5351B only Spread SpectrumI2C Interface I2C and Control SignalsI2C Write Operation Writing a Custom Configuration to RAM Configuring the Si5351Power-Up I2C Programming Procedure Replacing Crystals and Crystal Oscillators Si5351 Application ExamplesReplacing Crystals, Crystal Oscillators, and PLLs Replacing Crystals, Crystal Oscillators, and VCXOsSi5351B Si5351CHcsl Compatible Outputs Replacing a Crystal with a ClockDesign Considerations Trace Characteristics Register Register Map SummaryCLK0PHOFF70 Register Descriptions Register 1. Interrupt Status Sticky Clkin Loss Of Signal Sticky Bit Si5351C OnlySystem Calibration Status Sticky Bit Pllb Loss Of Lock Status Sticky BitRegister 2. Interrupt Status Mask Clkin Loss Of Signal Mask Si5351C OnlySystem Initialization Status Mask Pllb Loss Of Lock Status MaskOutput Disable for CLKx Register 3. Output Enable ControlRegister 9. OEB Pin Enable Control OEB pin enable control of CLKxPllbsrc Register 15. PLL Input SourceMultiSynth 0 Integer Mode Clock 0 Power DownRegister 16. CLK0 Control Bit Name FunctionMultiSynth 1 Integer Mode Clock 1 Power DownRegister 17. CLK1 Control MultiSynth Source Select for CLK1MultiSynth 2 Integer Mode Clock 2 Power DownRegister 18. CLK2 Control MultiSynth Source Select for CLK2MultiSynth 3 Integer Mode Clock 3 Power DownRegister 19. CLK3 Control MultiSynth Source Select for CLK3MultiSynth 4 Integer Mode Clock 4 Power DownRegister 20. CLK4 Control MultiSynth Source Select for CLK4MultiSynth 5 Integer Mode Clock 5 Power DownRegister 21. CLK5 Control MultiSynth Source Select for CLK5FBA MultiSynth Integer Mode Clock 7 Power DownRegister 22. CLK6 Control MultiSynth Source Select for CLK6Register 23. CLK7 Control FBB MultiSynth Integer ModeMultiSynth Source Select for CLK7 Output Clock 7 InvertBit Name Function CLKxDISSTATE Clock x Disable State Register 24. CLK3-0 Disable StateRegister 25. CLK7-4 Disable State Clock x Disable StateRegister 42. Multisynth0 Parameters Bit MS0P3158 Type Reset valueMS0P370 R0 Output Divider Register 44. Multisynth0 Parameters BitRegister 45. Multisynth0 Parameters Bit MS0P170 Register 46. Multisynth0 Parameters BitMS0P31916 MS0P21916 MS0P2158MS0P270 Register 49. Multisynth0 Parameters BitMS1P3158 MS1P370R1 Output Divider Register 52. Multisynth1 Parameters BitRegister 53. Multisynth1 Parameters Bit MS1P31916 MS1P21916 Register 54. Multisynth1 Parameters Bit Name MS1P170MS1P270 Register 57. Multisynth1 Parameters BitR2 Output Divider Register 60. Multisynth2 Parameters BitMultisynth2 Parameter Register 61. Multisynth2 Parameters BitMS2P31916 MS2P21916 Register 62. Multisynth2 Parameters Bit Name MS2P170MS2P270 Register 65. Multisynth2 Parameters BitMS3P3158 MS3P370R3 Output Divider Register 68. Multisynth3 Parameters BitRegister 69. Multisynth3 Parameters Bit MS3P31916 MS3P21916 Register 70. Multisynth3 Parameters Bit Name MS3P170MS3P270 Register 73. Multisynth3 Parameters BitMS4P3158 MS4P370R4 Output Divider Register 76. Multisynth4 Parameters BitRegister 77. Multisynth4 Parameters Bit MS4P31916 MS4P21916 Register 78. Multisynth4 Parameters Bit Name MS4P170MS4P270 Register 81. Multisynth4 Parameters BitMS5P3158 MS5P370R5 Output Divider Register 84. Multisynth5 Parameters BitRegister 85. Multisynth5 Parameters Bit MS5P31916 MS5P21916 Register 86. Multisynth5 Parameters Bit Name MS5P170MS5P270 Register 89. Multisynth5 Parameters BitMS6P170 MS7P170R7 Output Divider Register 92. Clock 6 and 7 Output Divider BitR6 Output Divider Clock 0 Initial Phase Offset Register 165. CLK0 Initial Phase OffsetRegister 166. CLK1 Initial Phase Offset Clock 1 Initial Phase OffsetClock 3 Initial Phase Offset Register 168. CLK3 Initial Phase OffsetRegister 169. CLK4 Initial Phase Offset Clock 4 Initial Phase OffsetPLLBReset Register 177. PLL ResetPLLAReset Register 183. Crystal Internal Load CapacitanceSi5351A Pin Descriptions Si5351A Pin Descriptions 20-Pin QFN, 24-Pin QsopPin Name Pin Number Pin Type Function 20-QFN Si5351B Pin Descriptions 10. Si5351B Pin Descriptions 20-Pin QFN, 24-Pin QsopSi5351C Pin Descriptions 11. Si5351C Pin Descriptions 20-Pin QFN, 24-Pin QsopSi5351A 10-MSOP Pin Descriptions 12. Si5351A Pin Descriptions 10-Pin MsopPin NumberDevice Part Numbers Ordering Information Si5351XDimension Min Nom Max Qsop Package DimensionsPackage Outline 24-Pin Qsop Dimension Min Nom Package DimensionsPackage Outline 20-Pin QFN Ddd Package Outline 10-Pin MsopRevision 0.9 to Revision Revision 0.1 to RevisionSi5351A/B/C Contact Information

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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