CS2300-CP_09 datasheet(18/32 Pages) CIRRUS

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CS2300-CP

DS843F1

Ratio modifiers which would produce an overflow or truncation of REFF should not be used; For example

if RUD is 1024 an RMOD of 8 would produce an REFF value of 8192 which exceeds the 4096 limit of the

12.20 format. In all cases, the maximum and minimum allowable values for REFF are dictated by the fre-

quency limits for both the input and output clocks as shown in the “AC Electrical Characteristics” on

page 7.

5.3.4

Ratio Configuration Summary

The RUD is the user defined ratio stored in the register space. The resolution for the RUD is selectable by

setting LFRatioCfg. R-Mod is applied if selected. The user defined ratio, and ratio modifier make up the

effective ratio REFF, the final calculation used to determine the output to input clock ratio. The conceptual

diagram in Figure 15 summarizes the features involved in the calculation of the ratio values used to gen-

erate the fractional-N value which controls the Frequency Synthesizer.

Figure 15. Ratio Feature Summary

Referenced Control

Ratio...................................... “Ratio (Address 06h - 09h)” on page 26

LFRatioCfg ............................ “Low-Frequency Ratio Configuration (LFRatioCfg)” on page 28

RModSel[2:0] ........................ “R-Mod Selection (RModSel[2:0])” section on page 25

Effective Ratio REFF

Ratio Format

Frequency Reference Clock

(CLK_IN)

PLL Output

Frequency

Synthesizer

Digital PLL &

Fractional N Logic

Ratio

12.20

20.12

LFRatioCfg

RModSel[2:0]

Ratio

Modifier

LCO

User Defined Ratio RUD

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