CS47L85 datasheet(237/370 Pages) CIRRUS

237 / 370 page

CS47L85

Rev 4.3

237

The MICD_BIAS_STARTTIME register should be set to 16ms or more if MICBn_RATE = 1 (pop-free start-up / shut-down).

The MICD_BIAS_STARTTIME register should be set to 0.25ms or more if MICBn_RATE = 0 (fast start-up / shut-down).

If the selected reference is not enabled continuously (i.e., if MICBn_ENA = 0), then the applicable MICBIAS discharge bit

(MICBn_DISCH) should be set to 0.

The MICBIAS sources are configured using the registers described in the “Charge Pumps, Regulators and Voltage

Reference

” section.

MICDET1

Accessory /

Button Detect

AGND

MICDET2

Detection pin selected by ACCDET_SRC:

(MICDET1 or MICDET2)

Microphone/Accessory detection

selected by ACCDET_MODE

Analogue Input

* INnx

Microphone Supply selected by

MICD_BIAS_SRC:

(MICVDD, MICBIAS1,

MICBIAS2, or MICBIAS3)

MICBIAS3

MICBIAS2

MICBIAS1

MICVDD

LDO2

Regulator

External accessories :-

2.2k



(+/-2%)

Microphone

Hookswitch

/ button 1

button 2

* Note that the IN1B or IN2B analogue

mic channel is recommended with the

external accessory detect function

Figure 70 Microphone and Accessory Detect Interface

When the discrete measurement mode is selected (ACCDET_MODE=000), the MICD_LVL_SEL [7:0] register bits allow

each of the impedance measurement levels to be enabled or disabled independently. This allows the function to be tailored

to the particular application requirements.

If one or more bits within the MICD_LVL_SEL register is set to 0, then the corresponding impedance level will be disabled.

Any measured impedance which lies in a disabled level will be reported as the next lowest, enabled level.

For example, the MICD_LVL_SEL [2] bit enables the detection of impedances around 73

. If MICD_LVL_SEL [2] = 0, then

an external impedance of 73

 will not be indicated as 73 but will be indicated as 40; this would be reported in the

MICD_LVL register as MICD_LVL [2] = 1.

With all measurement levels enabled, the CS47L85 can detect the presence of a typical microphone 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 71. 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).

CS47L85 Datasheet(PDF) 237 Page - Cirrus Logic

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