WM8955L
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STOPPING THE MASTER CLOCK
In order to minimise power consumed in the digital core of the WM8955L, the master clock should be
stopped in Standbyand OFF modes. If this is cannot be done externallyat the clock source, the
DIGENB bit (R25, bit 0) can be set to stop the MCLK signal from propagating into the device core.
However, since setting DIGENB has no effect on the power consumption of other system
components external to the WM8955L, it is preferable to disable the master clock at its source
wherever possible.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R25 (19h)
1
DIGENB
0
Master clock disable
Additional Control
(1)
0: master clock enabled
1: master clock disabled
Table 2 ADC andDAC Oversampling Rate Selection
NOTE: Before DIGENB can be set, the control bits DACL andDACR must be set to zero anda
waiting time of 1ms must be observed. Any failure to follow this procedure may prevent DACs
andADCs from re-starting correctly.
OVERSAMPLING RATE
Bydefault, the oversampling rate of the DAC digital filters is 128x. However, this can be changed to
64x bywriting to the DACOSR bit. In the 64x oversampling mode, the digital filters consumes less
power. However, the signal-to-noise ratio is slightlyreduced.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
0
DACOSR
0
DAC oversample rate select
1 = 64x (lowest power)
0 = 128x (best SNR)
Table 27 Oversampling Rate Selection
SAVING POWER AT LOW SUPPLY VOLTAGES
The analogue supplies to the WM8955L can run from 1.8V to 3.6V. Bydefault, all analogue circuitry
on the device is optimized to run at 3.3V. This set-up is also good for all other supplyvoltages down
to 1.8V. However, at lower voltages, it is possible to save power byreducing the internal bias
currents used in the analogue circuitry. This is controlled as shown below.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R23 (17h)
7:6
VSEL[1:0]
11
Analogue Bias optimization
Additional
Control(1)
00 : Lowest bias current, optimized for 1.8V
01 : Low bias current, optimized for 2.5V
10, 11 : Default bias current, optimized for 3.3V
Table 28 Analogue Bias Selection
Product Preview Rev 0.4 May2003
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
