WM8904
Pre-Production
MICROPHONE HOOK SWITCH DETECTION
The possibility of spurious hook switch interrupts due to ambient noise conditions can be removed by
careful understanding of microphone behaviour under extremely high sound pressure levels or during
mechanical shock, and by correct selection of the MICBIAS resistor value; these factors will affect the
level of the MICBIAS AC current spikes.
In applications where where the Current Detect threshold is close to the level of the current spikes,
the probability of false detections is reduced by the hysteresis and digital filtering described above.
Note that the filtering algorithm provides only limited rejection of very high current spikes at
frequencies less than or equal to the hook switch detect measurement frequency, or at frequencies
equal to harmonics of the hook switch detect measurement frequency.
The MICBIAS Hook Switch detection filtering is illustrated in Figure 26. Example control sequences
for configuring the Interrupts functions for MICBIAS current detection events are described in the
“Applications Information” section.
Figure 26 MICBIAS Hook Switch Detection Filtering
PP, Rev 3.3, September 2012
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
