WM8281ECSSLASHR datasheet(213/392 Pages) CIRRUS

213 / 392 page

WM8281

Rev 4.0

213

and up to 6 push-buttons. The microphone detect function is specifically designed to detect a video

accessory (typical 75

) load if required.

See “Applications Information” for typical recommended external components for microphone, video

or push-button accessory detection.

The accuracy of the microphone detect function is assured whenever the connected load is within the

applicable limits specified in the “Electrical Characteristics”. It is required that a 2.2k

 (2%) resistor

must also be connected between MICDET and the selected MICBIAS reference; note that different

resistor values will lead to inaccuracy in the impedance measurement.

Note that the connection of a microphone will change the measured impedance on the MICDET pin;

see “Applications Information” for recommended components for typical applications.

The measurement time varies between 100

s and 500s according to the impedance of the external

load. A high impedance will be measured faster than a low impedance.

The timing of the microphone detect function is illustrated in Figure 66. Two different cases are

shown, according to whether MICBIASn is enabled periodically by the impedance measurement

function (MICBn_ENA=0), or is enabled at all times (MICBn_ENA=1).

MICBn_ENA=0 :

MICBIASn is enabled periodically for measurement function

Measurement time

(100us to 500us)

MICD_RATE

(0ms to 512ms; 0.25ms default)

MICD_BIAS_STARTTIME

(0ms to 512ms; 0.25ms default)

time

MICBn_ENA=1 :

MICBIASn is enabled constantly

MICD_RATE

(0ms to 512ms; 0.25ms default)

time

Measurement time

(100us to 500us)

Figure 66 Microphone and Accessory Detect Timing

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