WM8903 datasheet(39/178 Pages) WOLFSON

39 / 178 page

Production Data

WM8903

PD, Rev 4.5, June 2012

The hook switch detection measurement frequency and the detection delay time tSHORT are detailed in

the “Electrical Characteristics” section.

The WM8903 Interrupt function is described in the “Interrupts” section. Example control sequences for

configuring the Interrupts functions for MICBIAS current detection events are described in the

“Applications Information” section.

A clock is required for the digital filtering function. This requires:



MCLK is present



CLK_SYS_ENA = 1



WSMD_CLK_ENA

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R22 (16h)

Clock Rates 2

CLK_SYS_ENA

System Clock enable

0 = Disabled

1 = Enabled

R108 (6Ch)

Write

Sequencer 0

WSMD_CLK_EN

Write Sequencer / Mic Detect Clock

Enable.

0 = Disabled

1 = Enabled

Table 8 MICBIAS Current Detect Clocking

Any MICBIAS Current Detect event (accessory insertion/removal or hookswitch press/release) which

happens while one or more of the clocking criteria is not satisfied (for example during a low power

mode where the CPU has disabled MCLK) will still be detected, but only after the clocking conditions

are met. An example is illustrated in Figure 26, where the mic is inserted while MCLK is stopped.

Figure 26 MICBIAS Detection Events without MCLK

MICROPHONE HOOK SWITCH DETECTION

The possibility of spurious hook switch interrupts due to ambient noise conditions can be removed by

careful understanding of the 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.

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