CS47L35 datasheet(157/300 Pages) CIRRUS

157 / 300 page

DS1085F3

157

CS47L35

4.12 External Accessory Detection

Figure 4-59. Microphone- and Accessory-Detect Interface

4.12.3.2 MICBIAS Reference Control

The voltage reference for the microphone detection is configured using the MICD_BIAS_SRC field, as described in

Table 4-77. The microphone detection function automatically enables the applicable reference when required for MICDET

impedance measurement.

If the selected reference (MICBIASnx) is not already enabled, the microphone detect circuit automatically enables the

respective MICBIAS output for short periods of time only, every time the impedance measurement is scheduled. To allow

time for the MICBIAS source to start-up, a time delay is applied before the measurement is performed; this is configured

using MICD_BIAS_STARTTIME, as described in Table 4-77.

Note: The microphone detection automatically enables the applicable MICBIASx generator (MICBIAS1 or MICBIAS2),

every time the impedance measurement is scheduled. The respective MICBIAS output switches are not controlled

automatically—the applicable switches must be enabled using the MICB1A_ENA, MICB1B_ENA or and MICB2A_

ENA bits, as described in Table 4-112.

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

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

The timing of the microphone detect function is shown in Fig. 4-60. Two different cases are shown, according to whether

MICBIASnx is enabled periodically by the impedance measurement function, or is enabled at all times.

If the selected reference (MICBIASnx) is not enabled continuously, the respective MICBIASnx discharge bits should be

cleared. The MICBIAS control registers are described in Section 4.19.

MICDET1

Accessory /

Button Detect

AGND

MICDET2

Detection pin selected by ACCDET_SRC:

(MICDET1 or MICDET2)

Microphone/Accessory detection

selected by ACCDET_MODE

Analog Input

* INnx

MICBIAS2A

MICBIAS1B

MICBIAS1A

MICVDD

LDO2

Regulator

External Accessories

2.2 k

(±2%)

Microphone

Hookswitch

/ Button 1

Button 2

* Note that the IN1Bxx analog mic

channels are recommended with the

external accessory detect function

Accessory-detect supply

source selected by

MICD_BIAS_SRC:

(MICVDD, MICBIAS1A,

MICBIAS1B, or MICBIAS2A)

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