WM5102 Datasheet, PDF (184/334 Pages) Wolfson Microelectronics plc – Audio Hub CODEC with Voice Processor DSP

WM5102
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start-up / shut-down). The MICD_BIAS_STARTTIME register should be set to 0.25ms or more if
MICBn_RATE = 0 (fast start-up / shut-down).
If the selected reference is not enabled continuously (ie. if MICBn_ENA = 0), then the applicable
MICBIAS discharge bit (MICBn_DISCH) should be set to 0.
The MICBIAS sources are configured using the registers described in the “Charge Pumps, Regulators
and Voltage Reference” section.
Figure 64 Microphone and Accessory Detect Interface
The MICD_LVL_SEL [7:0] register 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 within the MICD_LVL_SEL register is set to 0, then the corresponding impedance
level will be disabled. Any measured impedance which lies in a disabled level will be reported as the
next lowest, enabled level.
For example, the MICD_LVL_SEL [2] bit enables the detection of impedances around 73. If
MICD_LVL_SEL [2] = 0, then an external impedance of 73 will not be indicated as 73 but will be
indicated as 40; this would be reported in the MICD_LVL register as MICD_LVL [2] = 1.
With all measurement levels enabled, the WM5102 can detect the presence of a typical microphone
and up to 6 push-buttons. The microphone detect function is specifically designed to detect a video
accessory (typical 75) load if required.
See “Applications Information” for typical recommended external components for microphone, video
or push-button accessory detection.
The microphone detection circuit assumes that a 2.2k (2%) resistor is connected to the selected
MICBIAS reference, as illustrated. Different resistor values will lead to inaccuracy in the impedance
measurement.
The accuracy of the microphone detect function is assured whenever the connected load is within the
applicable limits specified in the “Electrical Characteristics”. It is required that a 2.2k (2%) resistor
must also be connected between MICDET and the selected MICBIAS reference; note that different
resistor values will lead to inaccuracy in the impedance measurement.
Note that the connection of a microphone will change the measured impedance on the MICDET pin;
see “Applications Information” for recommended components for typical applications.
The measurement time varies between 100s and 500s according to the impedance of the external
load. A high impedance will be measured faster than a low impedance.
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PD, June 2014, Rev 4.2
184