CS2300-CP Datasheet, PDF (16/32 Pages) Cirrus Logic – Fractional-N Clock Multiplier with Internal LCO

5.3.2
CS2300-CP
Manual Ratio Modifier (R-Mod)
The manual Ratio Modifier is used to internally multiply/divide the R_UD (the Ratio stored in the register
space remains unchanged). The available options for R_MOD are summarized in Table 2 on page 16.
The R-Mod value selected by RModSel[2:0] is always used in the calculation for the Effective Ratio
(R_EFF), see “Effective Ratio (REFF)” on page 17. If R-Mod is not desired, RModSel[2:0] should be left at
its default value of ‘000’, which corresponds to an R-Mod value of 1, thereby effectively disabling the ratio
modifier.
RModSel[2:0]
000
001
010
011
100
101
110
111
Ratio Modifier
1
2
4
8
0.5
0.25
0.125
0.0625
Table 2. Ratio Modifier
Referenced Control
Register Location
Ratio......................................“Ratio (Address 06h - 09h)” on page 27
RModSel[2:0] ........................“R-Mod Selection (RModSel[2:0])” section on page 25
5.3.3
Automatic Ratio Modifier (Auto R-Mod)
The Automatic R-Modifier uses the status of the CLK_IN Frequency Range Indicator (see section 5.2.1
on page 12) to implement a frequency dependent multiply of the currently addressed R_UD as shown in
Table 3.
Like with R-Mod, the Ratio stored in the register space remain unchanged. The Automatic Ratio-Modifier
is enabled by the AutoRMod bit.
FsDetect[1:0]
00
01
10
f_LCO / f_{CLK_IN}
> 224
96 - 224
< 96
Auto R Modifier
1
0.5
0.25
Table 3. Automatic Ratio Modifier
It is important to note that Auto R-Mod (if enabled) is applied in addition to any R-Mod already selected
by the RModSel[2:0] bits and is used to calculate the Effective Ratio (see Section 5.3.4 on page 17).
Auto R-Mod can be used to generate the appropriate oversampling clock (MCLK) for audio A/D and D/A
converters. For example, when the clock applied to CLK_IN is the audio sample rate, Fs (also known as
the word, frame or Left/Right clock), and the internal LCO is known to be between 13.23 MHz and 16.17
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