CS47L35 datasheet(154/300 Pages) CIRRUS

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154

DS1085F3

CS47L35

4.12 External Accessory Detection

Under typical use cases, the respective MICBIAS generator and headset audio paths should all be disabled

following jack removal.

After jack removal has been detected, the MICDET clamp override bit should be asserted (MICD_CLAMP_

OVD = 1), to make the system ready for a jack insertion.

The recommended control sequence for jack detect and MICDET clamp is summarized in Table 4-76.

4.12.3 Microphone Detect

The CS47L35 microphone detection circuit measures the impedance of an external load connected to one of the MICDET

pins. This feature can be used to detect the presence of a microphone, and the status of the associated hook switch. It

can also be used to detect push-button status or the connection of other external accessories.

4.12.3.1 Microphone Detect Control

The microphone detection circuit measures the impedance connected to MICDET1 or MICDET2. In the discrete

measurement mode (ACCDET_MODE = 000), the function reports whether the measured impedance lies within one of

eight predefined levels. In the ADC measurement mode (ACCDET_MODE = 111), a more specific result is provided in the

form of a 7-bit ADC output.

The microphone detection circuit typically uses one of the MICBIAS outputs as a reference. The CS47L35 automatically

enables the appropriate MICBIAS generator when required by the detection function; this allows the detection function to

be supported in low-power standby operating conditions.

Note that the MICVDD power domain must be enabled when using the microphone detection function. This power domain

is provided using an internal charge pump (CP2) and LDO regulator (LDO2). See Section 4.19 for details of these circuits.

The internal 32-kHz clock must be present and enabled when using the microphone detection function; see Section 4.16

for details.

To select microphone detection on one of the MICDET pins, ACCDET_MODE must be set to 000 or 111 (depending on

the desired measurement mode). The ACCDET_MODE field is defined in Table 4-77.

The CS47L35 can only support one headphone or microphone detection function at any time. When the detection function

is not in use, it is recommended to set ACCDET_MODE = 000.

The microphone detection circuit can be enabled on the MICDET1 pin or the MICDET2 pin, selected by using the

ACCDET_SRC bit.

The microphone detection circuit uses MICVDD, MICBIAS1A, MICBIAS1B, or MICBIAS2A as a reference. The applicable

source is configured using the MICD_BIAS_SRC field. Note that MICBIAS2B is not a valid reference source for the

microphone detection function.

When ACCDET_MODE is set to 000 or 111, microphone detection is enabled by setting MICD_ENA.

Table 4-76. Control Sequence for Jack Detect and MICDET Clamp

Event

Device Actions

Recommended User Actions

Initial condition

Clamp asserted by default

Configure MICDET_CLAMP_MODE

Jack insertion

Jack insertion signaled via IRQ

For headphone-only operation:

Enable output signal paths

For other use cases:

Disable clamp, MICD_CLAMP_OVD = 0

Enable MICBIAS and MICDET

Enable I/O signal paths

Jack removal

Jack removal signaled via IRQ

Clamp asserted automatically

Disable MICBIAS and MICDET

Disable I/O signal paths

Enable clamp MICD_CLAMP_OVD = 1

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