SI5325C-C-GM Datasheet, PDF(73/178 Page) Silicon Laboratories

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SI5325C-C-GM Datasheet, PDF (73/178 Pages) Silicon Laboratories – ANY-FREQUENCY PRECISION CLOCKS

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Si53xx-RM

6.5. Si5319, Si5324, Si5326, Si5327, Si5328, Si5368, Si5369, Si5374, Si5375, and Si5376

Free Run Mode

Si5319,

Si5324,

Si5326,

Si5327,

Si5368,

Si5369,

Si5374,

Si5375,

Si5376

CKIN1

CKIN2

Xtal osc

Crystal or external oscillator (external

oscillator only for the Si5374/75/76,

TCXO/OCXO only for the Si5328)

XA-XB

ï¸N31

ï¸N32

DSPLL

Core

CKOUT1

CKOUT2

Control

I2C/SPI

Figure 27. Free Run Mode Block Diagram

ï® CKIN2 has an extra mux with a path to the crystal oscillator output.

ï® When in Free Run mode, CKIN2 is sacrificed (Si5326, Si5368, Si5369, Si5374, and Si5376).

ï® Switching between the crystal oscillator and CLKIN1 is graceful and well-behaved.

ï® Either a crystal or an external oscillator can be used, except for the Si5374/75/76.

ï® External oscillator connection can be either single ended or differential.

ï® All other features and specifications remain the same.

6.5.1. Free Run Mode Programming Procedure

ï® Using DSPLLsim, determine the frequency plan:

ï¬ï Write to the internal dividers, including N31 and N32.

ï® Enable Free Run Mode (the mux select line), FREE_RUN.

ï® Select CKIN1 as the higher priority clock.

ï® Establish revertive and autoselect modes.

ï® Once properly programmed, the part will:

ï¬ï Initially lock to either the XA/XB (OSC_P and OSC_N for the Si5374/75/76) or to CKIN1.

ï¬ï Automatically select CKIN1, if it is available.

ï¬ï Automatically and hitlessly switch to XA/XB if CKIN1 fails.

ï¬ï Automatically and hitlessly switch back to CKIN1 when it subsequently returns.

ï® For the Si5319:

ï¬ï Clock selection is manual using an input pin.

ï¬ï Clock switching is not hitless.

ï¬ï CKIN2 is not available.

6.5.2. Clock Control Logic in Free Run Mode

Noting that the mux that selects CKIN2 versus the XA/XB oscillator is located before the clock selection and control

logic, when in Free Run mode operation, all such logic will be driven by the XA/XB oscillator, not the CKIN2 pins.

For example, when in Free Run mode, the CK2B pin will reflect the status of the XA/XB oscillator and not the status

of the CKIN2 pins.

Rev. 1.2

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