WM8510 Datasheet, PDF (45/56 Pages) Wolfson Microelectronics plc – MONO CODEC WITH SPEAKER DRIVER

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WM8510
The PLL frequency ratio R = f2/f1 (see Figure 27) can be set using the register bits PLLK and PLLN:
PLLN = int R
PLLK = int (2²⁴ (R-PLLN))
EXAMPLE:
MCLK=12MHz, required clock = 12.288MHz.
R should be chosen to ensure 5 < PLLN < 13. There is a fixed divide by 4 in the PLL and a
selectable divide by N after the PLL which should be set to divide by 2 to meet this requirement.
Enabling the divide by 2 sets the required f2 = 4 x 2 x 12.288MHz = 98.304MHz.
R = 98.304 / 12 = 8.192
PLLN = int R = 8
k = int ( 2²⁴ x (8.192 – 8)) = 3221225 = 3126E9h
REGISTER
ADDRESS
R36
PLL N value
BIT
4
3:0
LABEL
PLLPRESCALE
PLLN
R37
5:0
PLL K value 1
PLLK [23:18]
R38
8:0
PLL K Value 2
PLLK [17:9]
R39
8:0
PLLK [8:0]
PLL K Value 3
Table 30 PLL Frequency Ratio Control
DEFAULT
DESCRIPTION
0
1000
0Ch
093h
Divide MCLK by 2 before input to
PLL
Integer (N) part of PLL input/output
frequency ratio. Use values greater
than 5 and less than 13.
Fractional (K) part of PLL1
input/output frequency ratio (treat as
one 24-digit binary number).
0E9h
The PLL performs best when f2 is around 90MHz. Its stability peaks at N=8. Some example settings
are shown.
MCLK
(MHz)
(F1)
DESIRED
OUTPUT
(MHz)
F2
(MHz)
PRESCALE
DIVIDE
12
11.29
90.3168
1
12
12.288
98.304
1
13
11.29
90.3168
1
13
12.288
98.304
1
14.4
11.29
90.3168
1
14.4
12.288
98.304
1
19.2
11.29
90.3168
2
19.2
12.288
98.304
2
19.68
11.29
90.3168
2
19.68 12.288
98.304
2
19.8
11.29
90.3168
2
19.8
12.288
98.304
2
24
11.29
90.3168
2
24
12.288
98.304
2
26
11.29
90.3168
2
26
12.288
98.304
2
27
11.29
90.3168
2
27
12.288
98.304
2
Table 31 PLL Frequency Examples
POSTSCALE
DIVIDE
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
R
7.5264
8.192
6.947446
7.561846
6.272
6.826667
9.408
10.24
9.178537
9.990243
9.122909
9.929697
7.5264
8.192
6.947446
7.561846
6.690133
7.281778
N
(Hex)
7
8
6
7
6
6
9
A
9
9
9
9
7
8
6
7
6
7
K
(Hex)
86C227
3126E9
F28BD5
8FD526
45A1CB
D3A06D
6872B0
3D70A4
2DB493
FD80A0
1F76F8
EE009F
86C227
3126E9
F28BD5
8FD526
BOAC94
482297
w
PP Rev 1.2 December 2004
45