WM8962B datasheet(174/295 Pages) WOLFSON

174 / 295 page

WM8962

174

Rev 4.3

EXAMPLE PLL CALCULATION

A typical application may require a 12MHz clock output and a 24.576MHz clock output from the

WM8962.

In this case, it is recommended that PLL2 should be configured for 24MHz output. Under default

conditions, the CLKOUT2_DIV function will apply further division, enabling 12MHz output on the

CLKOUT2 pin.

The CLKOUT3 pin is suitable for 24.576MHz output, using the default values of the CLKOUT3_DIV

and PLL3_OUTDIV registers.

The following example illustrates how to derive the PLL registers to generate 24.000MHz output (FOUT)

from a 24.000 MHz reference clock (FREF).



Set PLLn_OUTDIV to ensure FVCO is in the range 90MHz to 100MHz.

FOUT = 24.000MHz, therefore PLLn_OUTDIV = 1 (divide by 4)



Calculate FVCO as given by FVCO = FOUT x PLLn_OUTDIV:-

FVCO = 24.000 x 4 = 96.000MHz



Calculate N.K as given by N.K = (FVCO x 2) / FREF:

N.K = (96.000 x 2) / 24 = 8.0



Determine PLLn_N and PLLn_K from the integer and fractional portions of N.K:-

PLLn_N = 8. PLLn_K = 0.0



N.K is an integer; set PLLn_FRAC = 0.

The following example illustrates how to derive the PLL registers to generate 24.576MHz output (FOUT)

from a 24.000 MHz reference clock (FREF).



Set PLLn_OUTDIV to ensure FVCO is in the range 90MHz to 100MHz.

FOUT = 24.576MHz, therefore PLLn_OUTDIV = 1 (divide by 4)



Calculate FVCO as given by FVCO = FOUT x PLLn_OUTDIV:-

FVCO = 24.576 x 4 = 98.304MHz



Calculate N.K as given by N.K = (FVCO x 2) / FREF:

N.K = (98.304 x 2) / 24 = 8.192



Determine PLLn_N and PLLn_K from the integer and fractional portions of N.K:-

PLLn_N = 8. PLLn_K = 0.192



Confirm that N.K is a fractional quantity and set PLLn_FRAC:

N.K is fractional. Set PLLn_FRAC = 1.



Convert PLL_K into integer format:

0.192 x 16777216 = 3221225.472 (decimal).



Round off to 3221225 (decimal) = 3126E9h

PLLn_K [23:16] = 31h

PLLn_K [15:8] = 26h

PLLn_K [7:0] = E9h

WM8962B Datasheet(PDF) 174 Page - Wolfson Microelectronics plc

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