WM8903LGEFK/RV Wolfson Microelectronics, WM8903LGEFK/RV Datasheet - Page 38

• Manufacturer Part Number: WM8903LGEFK/RV
• Description: Audio CODECs ULTRA LOW PWR HI FI CODEC
• Manufacturer: Wolfson Microelectronics

Specifications of WM8903LGEFK/RV

• Audio Codec Type: Stereo Codec
• No. Of Adcs: 2
• No. Of Dacs: 2
• No. Of Input Channels: 6
• No. Of Output Channels: 8
• Adc / Dac Resolution: 24bit
• Sampling Rate: 96kHz
• Operating Temperature Range: -40°C To +85°C
• Rohs Compliant: Yes
• Adcs / Dacs Signal To Noise Ratio: 96dB
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

WM8903
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Table 7 MICBIAS Current Detect
MICBIAS CURRENT DETECT FILTERING
The function of the filtering is to ensure that AC current spikes caused by ambient noise conditions
near the microphone do not lead to incorrect signalling of the microphone insertion/removal status or
the microphone hookswitch status.
Hysteresis on the current thresholds is provided; this means that a different current threshold is used
to detect microphone insertion and microphone removal. Similarly, a different current threshold is
used to detect hookswitch press and hookswtich release.
Digital filtering of the hookswitch status ensures that the MICBIAS Short Circuit detection event is
only signalled if the MICSHORT_THR threshold condition has been met for 10 consecutive
measurements.
In a typical application, microphone insertion would be detected when the MICBIAS current exceeds
the Current Detect threshold set by MICDET_THR.
When the MICDET_INV interrupt polarity bit is set to 0, then microphone insertion detection will
cause the MICDET_EINT interrupt status register to be set.
For detection of microphone removal, the MICDET_INV bit should be set to 1. When the
MICDET_INV interrupt polarity bit is set to 1, then microphone removal detection will cause the
MICDET_EINT interrupt status register to be set.
The detection of these events is bandwidth limited for best noise rejection, and is subject to detection
delay time t
has been set appropriately, each insertion or removal event is guaranteed to be detected within the
delay time t
It is likely that the microphone socket contacts will have mechanical “bounce” when a microphone is
inserted or removed, and hence the resultant control signal will not be a clean logic level transition.
Since t
mechanical “bounce” has ceased. Hence after a mic insertion or removal has been detected, a time
delay should be applied before re-configuring the MICDET_INV bit. The maximum possible
mechanical bounce times for mic insertion and removal must be understood by the software
programmer.
Utilising a GPIO pin to monitor the steady state of the microphone detection function does not
change the timing of the detection mechanism, so there will also be a delay t
changes state. It may be desirable to implement de-bounce in the host processor when monitoring
the state of the GPIO signal.
Microphone hook switch operation is detected when the MICBIAS current exceeds the Short Circuit
Detect threshold set by MICSHORT_THR. Using the digital filtering, the hook switch detection event
is only signalled if the MICSHORT_THR threshold condition has been met for 10 consecutive
measurements.
When the MICSHRT_INV interrupt polarity bit is set to 0, then hook switch operation will cause the
MICSHRT_EINT interrupt status register to be set.
For detection of microphone removal, the MICSHRT_INV bit should be set to 1. When the
MICSHRT_INV interrupt polarity bit is set to 1, then hook switch release will cause the
MICSHRT_EINT interrupt status register to be set.
REGISTER
ADDRESS
DET
DET
has a range of values, it is possible that the interrupt will be generated before the
DET
.
, as specified in the “Electrical Characteristics”. Provided that the MICDET_THR field
BIT
1
MICDET_ENA
LABEL
DEFAULT
0
MICBIAS Current and Short Circuit
Detect Enable
0 = disabled
1 = enabled
PD, Rev 4.0, September 2010
DESCRIPTION
DET
before the signal
Production Data
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