CS47L35 datasheet(158/300 Pages) CIRRUS

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DS1085F3

CS47L35

4.12 External Accessory Detection

Figure 4-60. Microphone- and Accessory-Detect Timing

4.12.3.3 Measurement Range Control

When the discrete measurement mode is selected (ACCDET_MODE = 000), the MICD_LVL_SEL[7:0] 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 MICD_LVL_SEL is cleared, the corresponding impedance level is disabled. Any measured impedance

which lies in a disabled level is reported as the next lowest, enabled level.

For example, the MICD_LVL_SEL[2] bit enables the detection of a 360–680

 impedance. If MICD_LVL_SEL[2] = 0, an

external impedance in this range is indicated in the next lowest detection range (210–290

); this would be reported in the

MICD_LVL field as MICD_LVL[2] = 1.

With default register configuration, and all measurement levels enabled, the CS47L35 can detect the presence of a typical

microphone and up to four push buttons. It is possible to configure the detection circuit for up to eight push buttons, by

adjusting the impedance detection thresholds. However, adjustment of the detection thresholds is outside the scope of

this datasheet—please contact your local Cirrus Logic representative for further information, if required.

The measurement time varies between 100–500

s, depending on the impedance of the external load, and depending on

how many impedance measurement levels are enabled. A high impedance is measured faster than a low impedance.

4.12.3.4 External Components

The external connections for the microphone detect circuit are shown in Fig. 4-59. Examples of suitable external

components are described in Section 5.1.8.

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

specified in Table 3-11. It is required that a 2.2-k

 (2%) resistor must also be connected between MICDET and the

selected MICBIAS reference—different resistor values lead to inaccuracy in the impedance measurement.

MICBn_ENA = 0, MICBnx_ENA = 1:

MICBIASnx is enabled periodically for

measurement function

MICD_RATE

(0 ms to 512 ms; 0.25 ms default)

MICD_BIAS_STARTTIME

(0 ms to 512 ms; 0.25 ms default)

time

MICBn_ENA = 1, MICBnx_ENA = 1:

MICBIASnx is enabled constantly

MICD_RATE

(0 ms to 512 ms; 0.25 ms default)

time

Measurement time

(100

s to 500 s)

Measurement time

(100

s to 500 s)

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