SI5338 Datasheet, PDF(26/170 Page) Silicon Laboratories – I2C-PROGRAMMABLE ANY-FREQUENCY, ANY-OUTPUT QUAD CLOCK GENERATOR

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SI5338 Datasheet, PDF (26/170 Pages) Silicon Laboratories – I2C-PROGRAMMABLE ANY-FREQUENCY, ANY-OUTPUT QUAD CLOCK GENERATOR

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Si5338

4.2. Synchronous Frequency Translation

In other cases, it is useful to generate an output

frequency that is synchronous (or phase-locked) to

another clock frequency. The Si5338 is the ideal choice

for generating up to four clocks with different

frequencies with a fixed phase relationship to an input

reference. Because of its highly precise frequency

synthesis, the Si5338 can generate all four output

frequencies with 0 ppm error to the input reference. The

Si5338 is an ideal choice for applications that have

traditionally required multiple stages of frequency

synthesis to achieve complex frequency translations.

Examples are in broadcast video (e.g., 148.5 MHz to

148.351648351648 MHz), WAN/LAN applications (e.g.

155.52 MHz to 156.25 MHz), and Forward Error

Correction (FEC) applications (e.g., 156.25 MHz to

161.1328125 MHz). Using the input reference selectors,

the Si5338 can select from one of four inputs (IN1/IN2,

IN3, IN4, and IN5/IN6). Figure 17 shows the Si5338

configured as a synchronous clock generator.

Frequencies and multiplication ratios may be entered

into ClockBuilder Desktop using fractional notation to

ensure that the exact scaling ratios can be achieved.

Si5338

Fin

M0 R0

M1 R1

ref PLL

M2 R2

M3 R3

4.3. Configurable Buffer and Level

Translator

Using the output selectors, the synthesis stage can be

entirely bypassed allowing the Si5338 to act as a

configurable clock buffer/divider with level translation

and selectable inputs. Because of its highly selectable

configuration, virtually any combination is possible. The

configurable output drivers allow four differential

outputs, eight single-ended outputs, or a combination of

both. Figure 18 shows the Si5338 configured as a

flexible clock buffer.

S i5 3 3 8

F in

F in * 1

Figure 18. Si5338 as a Configurable Clock

Buffer/Divider with Level Translation

4.3.1. Combination Free-Running and Synchronous

Clock Generator

Another application of the Si5338 is in generating both

free-running and synchronous clocks in one device.

This is accomplished by configuring the input and

output selectors for the desired split configuration. An

example of such an application is shown in Figure 19.

Figure 17. Si5338 as a Synchronous Clock

Generator or Frequency Translator

XTAL

Si5338

Osc

Fin

P2 ref PLL

Figure 19. Si5338 In a Free-Running and

Synchronous Clock Generator Application

Rev. 0.6

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