CS47L85 datasheet(233/370 Pages) CIRRUS

233 / 370 page

CS47L85

Rev 4.3

233

The recommended control sequence for Jack Detect and MICDET Clamp is summarised in Table 87.

EVENT

DEVICE ACTIONS

RECOMMENDED USER ACTIONS

Initial condition

Clamp asserted by default

Configure MICDET_CLAMP_MODE

Jack insertion

Jack insertion signalled via IRQ

For headphone-only operation:

Enable output signal paths

For other use cases:

Disable clamp MICD_CLAMP_OVD = 0

Enable MICBIAS / MICDET

Enable input / output signal paths

Jack removal

Jack removal signalled via IRQ

Clamp asserted automatically

Disable MICBIAS / MICDET

Disable input / output signal paths

Enable clamp MICD_CLAMP_OVD = 1

Table 87 Control Sequence for Jack Detect and MICDET Clamp

MICROPHONE DETECT

The CS47L85 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 hookswitch. It can

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

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 8 pre-

defined 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 CS47L85 will automatically

enable the appropriate MICBIAS when required in order to perform 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 “Charge Pumps, Regulators and Voltage

Reference

” for details of these circuits. The internal 32kHz clock must be present and enabled when using the microphone

detection function: see “Clocking and Sample Rates” for details.

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

(depending on the desired measurement mode). The ACCDET_MODE register is defined in Table 88.

The CS47L85 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 the ACCDET_SRC

The microphone detection circuit uses MICVDD, MICBIAS1, MICBIAS2 or MICBIAS3 as a reference. The applicable source

is configured using the MICD_BIAS_SRC register. Note that MICBIAS4 is not a valid reference source for the microphone

detection function.

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

When microphone detection is enabled, the CS47L85 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

detection result has settled, the CS47L85 indicates valid data by setting the MICD_VALID bit.

When the discrete measurement mode is selected (ACCDET_MODE=000), the measured impedance is only deemed valid

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

of the de-bounce period; this can be either 2 measurements or 4 measurements.

When the microphone detection result has settled (i.e., after the applicable de-bounce period), the CS47L85 indicates valid

data by setting the MICD_VALID bit. The measured impedance is indicated using the MICD_LVL and MICD_STS register

bits, as described in Table 88.

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, then the MICD_LVL and MICD_STS fields will change, but the

MICD_VALID bit will remain set, indicating valid data at all times.

The 8 pre-

defined impedance levels (including the ‘no accessory detected’ level) allow detection of a typical microphone

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