WM8904ECSSLASHR datasheet(46/188 Pages) WOLFSON

46 / 188 page

WM8904

Pre-Production

PP, Rev 3.3, September 2012

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

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