WM8903 datasheet(175/178 Pages) WOLFSON

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Production Data

WM8903

PD, Rev 4.5, June 2012

175

STEP

DETAILS

Mic not inserted. To detect mic insertion, Host processor must initialise interrupts and clear MICDET_INV = 0. At every

step, the host processor should poll the interrupt status register.

Mechanical bounce of jack socket during Mic insertion. Host processor may already detect a mic insertion interrupt

(MICDET_EINT) during this step. Once detected, the host processor can set MICDET_INV = 1, unless mechanical

bounce can last longer than the shortest possible TDET, in which case the host processor should not set MICDET_INV = 1

until step 3.

Mic fully inserted. If not already set, the host processor must now set MICDET_INV = 1. To detect Hook switch press, the

host processor must clear MICSHRT_INV = 0. At this step, the diagram shows no AC current swing, due to a very low

ambient noise level.

Mic fully inserted. Diagram shows AC current swing due to high levels of background noise (such as wind).

Mechanical bounce during hook switch press. The hook switch interrupt is unlikely to be set during this step, because 10

successive samples of the MICBIAS current exceeding the hook switch threshold have not yet been sampled.

Hook switch is fully pressed down. After TSHORT, 10 successive samples of the MICBIAS current exceeding the hook

switch threshold have been detected, hence a hook switch interrupt (MICSHRT_EINT) will be generated, and the host

processor can immediately set MICSHRT_INV = 1.

Mechanical bounce during hook switch release. The hook switch interrupt is unlikely to be set during this step, because

10 successive samples of the MICBIAS current lower than the hook switch threshold have not yet been sampled.

Hook switch fully released. After TSHORT, 10 successive samples of the MICBIAS current lower than the hook switch

threshold have been detected, hence a hook switch interrupt (MICSHRT_EINT) will be generated, and the host processor

can immediately clear MICSHRT_INV = 0.

Mechanical bounce of jack socket during Mic removal. Host processor may already detect a mic removal interrupt

(MICDET_EINT) during this step. Once detected, the host processor can clear MICDET_INV = 0, unless mechanical

bounce can last longer than the shortest possible TDET, in which case the host processor should not clear MICDET_INV =

0 until step 10.

Mic fully removed. If not already cleared, the host processor must now clear MICDET_INV = 0.

Table 86 Mic Insert and Hook Switch Detect: Example Sequence

Alternatively, utilising a GPIO pin to monitor the MICBIAS current detect functionality permits the host

processor to monitor the steady state of microphone detection or hook switch press functions.

Because the GPIO shows the steady state condition, software de-bounce may be easier to implement

in the host processor, dependant on the processor performance characteristics, hence use of the

GPIO is likely to simplify the rejection of mechanical bounce. Changes of state in the GPIO pin are

also subject to the time delays tDET and tSHORT.

Further details can be found in the applications note WAN_0213 “WM8903 ECM mic detection using

MICBIAS current”.

WM8903 Datasheet(PDF) 175 Page - Wolfson Microelectronics plc