WM8955BL
Production Data
The PLL frequency ratio R = f2/f1 (see Figure 17) can be set using K and N in registers 44 (2Ch) to 46
(2Eh):
N = int (R)
K = int (222 (R-N))
Example:
MCLK = 12MHz required clock = 12.288MHz
R should be chosen to ensure 5<N<13. There is a divide by 4 and selectable divide by 2 after the
PLL which should be set to meet this requirement. Enabling the divide by 2 sets the required f2 = 8x
12.288MHz = 98.304MHz.
R = 98.304/12 = 8.192
N = intR = 8
K = int (222 x (8.192-8)) = 805306 = C49BAh.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R44 (2Ch)
N
Integer part of PLL input/output
frequency ratio. Use values greater
than 5 and less than 13.
8:5
1000
PLL Control (1)
K [21:18]
K [17:9]
Fractional part of PLL input/output
frequency ratio (treat as one 22-digit
binary number)
3:0
8:0
0011
024h
R45 (2Dh)
PLL Control (2)
R46 (2Eh)
K [8:0]
KEN
8:0
7
1BAh
0
PLL Control (3)
R59 (3Bh)
0: Fractional part (K) disabled
1: K enabled
Table 20 PLL Frequency Ratio Control
The PLL performs best when f2 is around 90MHz. Its stability peaks at N=8. Some example settings
are shown below.
MCLK
DESIRED
OUTPUT
(MHz)
F2
MCLK
DIV2
PLL
OUT
DIV2
R
F2
K
(MHz)
(MHz)
(Hex)
(Hex)
11.91
11.91
12
11.2896
12.288
11.2896
12.288
11.2896
12.288
11.2896
12.288
11.2896
12.288
11.2896
12.288
11.2896
12.288
11.2896
12.288
11.2896
12.288
11.2896
12.288
90.3168
98.304
90.3168
98.304
90.3168
98.304
90.3168
98.304
90.3168
98.304
90.3168
98.304
90.3168
98.304
90.3168
98.304
90.3168
98.304
90.3168
98.304
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
7.5833
8.2539
7.5264
8.192
7
8
7
8
6
7
6
6
9
A
9
9
9
9
7
8
6
7
6
7
25545C
103FF6
21B089
C49BA
3CA2F4
23F548
116872
34E818
1A1CAC
F5C28
12
13
6.9474
7.5618
6.272
13
14.4
14.4
19.2
19.2
19.68
19.68
19.8
19.8
24
6.8267
9.408
10.24
9.1785
9.9902
9.1229
9.9297
7.5264
8.192
B6D22
3F6017
7DDCA
3B8023
21B089
C49BA
3CA2F4
23F548
2C2B30
12089E
24
26
6.9474
7.5618
6.6901
7.2818
26
27
27
Table 21 PLL Frequency Examples
PD Rev 4.1 February 2007
30
w
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
