CS47L35 datasheet(155/300 Pages) CIRRUS

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DS1085F3

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CS47L35

4.12 External Accessory Detection

When microphone detection is enabled, the CS47L35 performs a number of measurements in order to determine the

MICDET impedance. The measurement process is repeated at a cyclic rate controlled by MICD_RATE. The MICD_RATE

field selects the delay between completion of one measurement and the start of the next. When the microphone detection

result has settled, the CS47L35 indicates valid data by setting MICD_VALID.

The discrete measurement mode and ADC measurement mode provide different capabilities for microphone detection.

The control requirements and the measurement indication mechanisms differ according to the selected mode, as follows:

• In the discrete measurement mode (ACCDET_MODE = 000), the measured impedance is only deemed valid after

more than one successive measurement has produced the same result. The MICD_DBTIME field provides control

of the debounce period; this can be either two measurements or four measurements.

When the microphone detection result has settled (i.e., after the applicable debounce period), the CS47L35

indicates valid data by setting the MICD_VALID bit. The measured impedance is indicated using the MICD_LVL and

MICD_STS bits, as described in Table 4-77.

The MICD_VALID bit, when set, remains asserted for as long as the microphone detection function is enabled (i.e.,

while MICD_ENA = 1). If the detected impedance changes, the MICD_LVL and MICD_STS fields change, but the

MICD_VALID bit remains set, indicating valid data at all times.

The detection circuit supports up to eight impedance levels (including the no-accessory-detected level), enabling

detection of a typical microphone and up to six push buttons. Each measurement level can be enabled or disabled

independently; this provides flexibility according to the required thresholds, and offers a faster measurement time

in some applications. The MICD_LVL_SEL field is described in Section 4.12.3.3. The default configuration supports

a maximum of four push buttons, in accordance with the Android headset specification for accessory push-button

operation.

Note that, for typical headset detection, the choice of external resistance values must take into account the

impedance of the microphone—the detected impedance corresponds to the combined parallel resistance of the

microphone and any asserted push button. Examples of suitable external components are described in

Section 5.1.8.

• In the ADC measurement mode (ACCDET_MODE = 111), the detection function generates two output results,

contained within the MICDET_ADCVAL and MICDET_ADCVAL_DIFF fields. These fields contain the most recent

measurement value (MICDET_ADCVAL) and the measurement difference value (MICDET_ADCVAL_DIFF). The

difference value indicates the difference between the latest measurement and the previous measurement; this can

be used to determine whether the measurement is stable and reliable.

In ADC measurement mode, the detection function must be disabled before the measurement can be read. When

the CS47L35 indicates valid data (MICD_VALID = 1), the detection must be disabled by setting MICD_ENA = 0.

Note that MICDET_ADCVAL and MICDET_ADCVAL_DIFF do not follow a linear coding. The appropriate test

condition for accepting the measurement value (or for rescheduling the measurement) varies depending on the

application requirements, and depending on the expected impedance value.

The microphone detection function is an input to the interrupt control circuit and can be used to trigger an interrupt event

every time an accessory insertion, removal, or impedance change is detected; see Section 4.15.

The fields associated with microphone detection (or other accessories) are described in Table 4-77. The external circuit

configuration is shown in Fig. 4-59.

Table 4-77. Microphone Detect Control

Address

Bit

Label

Default

Description

R659 (0x0293)

Accessory_

Detect_Mode_

ACCDET_SRC

Accessory Detect/Headphone Feedback pin select

0 = Accessory detect on MICDET1; Headphone ground feedback on HPOUTFB1

1 = Accessory detect on MICDET2; Headphone ground feedback on HPOUTFB2

2:0

ACCDET_

MODE[2:0]

000

Accessory Detect Mode Select

000 = Mic detect (MICDETn, discrete mode)

001 = Headphone detect (HPDETL)

010 = Headphone detect (HPDETR)

011 = Reserved

100 = Headphone detect (MICDETn)

101 = Reserved

110 = Reserved

111 = Mic detect (MICDETn, ADC mode)

Note that the MICDETn measurements are implemented on either the MICDET1 or

MICDET2 pins, depending on the ACCDET_SRC bit.

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