CS2300-OTP_09 Datasheet, PDF (14/26 Pages) Cirrus Logic – Fractional-N Clock Multiplier with Internal LCO

CS2300-OTP
Ratio modifiers which would produce an overflow or truncation of R_EFF should not be used. In all cases,
the maximum and minimum allowable values for R_EFF are dictated by the frequency limits for both the
input and output clocks as shown in the “AC Electrical Characteristics” on page 7.
Selection of the user defined ratio from the four stored ratios is made by using the M[1:0] pins.
Referenced Control
Parameter Definition
M[1:0] pins.............................“M1 and M0 Mode Pin Functionality” on page 16
5.4.4 Ratio Configuration Summary
The R_UD is the user defined ratio for which up to four different values (Ratio_0-3) can be stored in the one
time programmable memory. The M[1:0] pins then select the user defined ratio to be used as well as the
modal configuration set. The resolution/format for the R_UD is selectable. R-Mod is applied accordingly.
The user defined ratio, ratio modifier, and automatic ratio modifier make up the effective ratio R_EFF, the
final calculation used to determine the output to input clock ratio. The conceptual diagram in Figure 10
summarizes the features involved in the calculation of the ratio values used to generate the fractional-N
value which controls the Frequency Synthesizer. The subscript ‘4’ indicates the modal parameters.
Effective Ratio REFF
M[1:0] pins
User Defined Ratio RUD
Ratio 0
Ratio 1
Ratio 2
Ratio Format
12.20
20.12
Ratio 3
LFRatioCfg
M2 pin
RModSel[1:0]4
Ratio
Modifier
LCO
Digital PLL &
Fractional N Logic
Dynamic Ratio, ‘N’
Frequency Reference Clock
(CLK_IN)
Frequency
Synthesizer
PLL Output
Figure 10. Ratio Feature Summary
Referenced Control
Parameter Definition
Ratio 0-3................................“Ratio 0 - 3” on page 20
M[1:0] pins.............................“M1 and M0 Mode Pin Functionality” on page 16
LFRatioCfg ............................“Low-Frequency Ratio Configuration (LFRatioCfg)” on page 20
RModSel[1:0] ........................“R-Mod Selection (RModSel[1:0])” section on page 19
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