CS2200-CP_09 Datasheet, PDF (14/26 Pages) Cirrus Logic – Fractional-N Frequency Synthesizer

5.2.4
CS2200-CP
Ratio Configuration Summary
The R_UD is the user defined ratio stored in the register space. R-Mod is applied if selected. The user de-
fined ratio, and ratio modifier make up the effective ratio R_EFF, the final calculation used to determine the
output to input clock ratio. The effective ratio is then corrected for the internal dividers. The conceptual
diagram in Figure 8 summarizes the features involved in the calculation of the ratio values used to gen-
erate the fractional-N value which controls the Frequency Synthesizer.
Timing Reference Clock
(XTI/REF_CLK)
Effective Ratio REFF
User Defined Ratio RUD
Ratio
Ratio Format
12.20
RModSel[2:0]
Ratio
Modifier
Divide
RefClkDiv[1:0]
RefClkDiv[1:0]
R Correction
SysClk
N
Frequency
Synthesizer
PLL Outpu
Figure 8. Ratio Feature Summary
Referenced Control
Register Location
Ratio......................................“Ratio (Address 06h - 09h)” on page 21
RModSel[2:0] ........................“R-Mod Selection (RModSel[2:0])” section on page 20
RefClkDiv[1:0] .......................“Reference Clock Input Divider (RefClkDiv[1:0])” on page 22
5.3 PLL Clock Output
The PLL clock output pin (CLK_OUT) provides a buffered version of the output of the frequency synthesizer.
The driver can be set to high-impedance with the ClkOutDis bit.
The output from the PLL automatically drives a static low condition while the PLL is un-locked (when the
clock may be unreliable). This feature can be disabled by setting the ClkOutUnl bit, however the state
CLK_OUT may then be unreliable during an unlock condition.
ClkOutUnl
PLL Locked/Unlocked
0
0
2:1 Mux
1
0
2:1 Mux
ClkOutDis
PLL Clock Output
PLLClkOut
PLL Clock Output Pin
(CLK_OUT)
PLL Output
1
Figure 9. PLL Clock Output Options
Referenced Control
Register Location
ClkOutUnl..............................“Enable PLL Clock Output on Unlock (ClkOutUnl)” on page 22
ClkOutDis ..............................“PLL Clock Output Disable (ClkOutDis)” on page 20
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