XWM8739SEDS/V View Datasheet(PDF) - Cirrus Logic
Part Name
Description
MFG CO.
'XWM8739SEDS/V' PDF : 37 Pages View PDF
WM8739
USB MODE SAMPLE RATES
In USB mode the MCLK/crystal oscillator input is 12MHz only.
SAMPLING
RATE
kHz
48
MCLK
FREQUENCY
MHz
12.000
BOSR
0
SAMPLE
RATE
REGISTER SETTINGS
SR3 SR2 SR1
0
0
0
Production Data
DIGITAL
FILTER
TYPE
SR0
0
0
44.1 (Note 2)
12.000
1
1
0
0
0
1
8
12.000
0
0
0
1
0
0
8 (Note 1)
12.000
1
1
0
1
0
1
32
12.000
0
0
1
1
0
0
96
12.000
0
0
1
1
1
3
88.2 (Note 3)
12.000
1
1
1
1
1
2
Table 10 USB Mode Sample Rate Look-up Table
Notes:
1. 8k not exact, actual = 8.021kHz
2. 44.1k not exact, actual = 44.118kHz
3. 88.2k not exact, actual = 88.235kHz
4. All other combinations of BOSR and SR[3:0] that are not in the truth table are invalid
The table above can be used to set up the device to work with various sample rate combinations. For
example if the user wishes to use the WM8739 in USB mode with the ADC sample rate at 48kHz,
then the device should be programmed with BOSR = 0, SR3 = 0, SR2 = 0, SR1 = 0 and SR0 = 0.
The ADC will then operate with a Digital Filter of type 0, refer to Digital Filter Characteristics section
for an explanation of the different filter types.
The BOSR bit represents the base over-sampling rate. This is the rate that the WM8739 digital signal
processing is carried out at and the sampling rate will always be a sub-multiple of this. In USB mode,
with BOSR = 0, the base over-sampling rate is defined at 250fs, with BOSR = 1, the base over-
sampling rate is defined at 272fs. This can be used to determine the actual audio sampling rate
produced by the ADC.
Example scenarios are:
1. with a requirement that the ADC data sampling rate is 8kHz the device is programmed with
BOSR = 0 (250fs), SR3 = 0, SR2 = 0, SR1 = 1, SR0 = 0.The ADC will then be exactly 8kHz
(derived from 12MHz/250 x 1/6).
2. with a requirement that ADC data rate is 8kHz the device is programmed with BOSR = 1
(272fs), SR3 = 0, SR2 = 0, SR1 = 1, SR0 = 0. The ADC will not output data at exactly 8kHz,
instead it will be 8.021kHz (derived from 12MHz/272 x 2/11). A slight (sub 0.5%) pitch shift will
therefore result in the 8kHz audio data and (more importantly) the user must ensure that the
data across the digital interface is correctly synchronised at the 8.021kHz rate.
w
PD, Rev 4.2, July 2008
24
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