WM8903LGEFK/RV Wolfson Microelectronics, WM8903LGEFK/RV Datasheet - Page 32

• 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
ELECTRET CONDENSER MICROPHONE INTERFACE
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Electret Condenser microphones may be connected as single-ended or differential inputs to the Input
PGAs described in the “Analogue Input Signal Path” section. The WM8903 provides a low-noise
reference voltage suitable for biasing electret condenser microphones. This is provided on the
MICBIAS pin, and can be enabled using the MICBIAS_ENA register bit.
MICBIAS CURRENT DETECT FUNCTION
Insertion/removal of a microphone or pressing/releasing a hook switch button will cause a significant
change of MICBIAS current flow. Two current thresholds are provided, set by MICDET_THR and
MICSHORT_THR. When a change of current which crosses either threshold is detected, an interrupt
event can be generated. In a typical application, accessory insertion would be detected when the
MICBIAS current exceeds MICDET_THR, and microphone hookswitch operation would be detected
when the MICBIAS current exceeds MICSHORT_THR.
The Threshold Detection functions are both inputs to the Interrupt control circuit and can be used to
trigger an Interrupt event when MIC_DET_ENA=1 - see “Interrupts”. The interrupt flag can be read
back via the control interface, or the microphone status can be read back via a GPIO pin - see
“General Purpose Input/Output (GPIO)”.
Hysteresis and digital filtering are implemented in the hook switch detect circuit to improve reliability
in conditions where AC current spikes are present due to ambient noise conditions. Hysteresis and
digital filtering applies to both methods of detection, i.e. interrupt events, or GPIO pin state.
The register fields used to configure MICBIAS functionality are described in Table 6. Performance
parameters for this circuit block can be found in the “Electrical Characteristics” section.
Further guidance on the usage of the MICBIAS current monitoring features is described on the
following pages.
Table 6 MICBIAS Control
R6 (06h)
Mic Bias
Control 0
REGISTER
ADDRESS
BIT
7:6
5:4
3:2
1
0
Reserved
MICDET_THR
[1:0]
MICSHORT_TH
R [1:0]
MICDET_ENA
MICBIAS_ENA
LABEL
DEFAULT
00
00
00
0
0
Reserved. Writing ‘1’ to these
register bits will have no effect.
MICBIAS Current Detect Insertion
Threshold
00 = 0.063mA
01 = 0.26mA
10 = 0.45mA
11 = 0.635mA
If AVDD
MICBIAS Short Circuit Button Push
Threshold
00 = 0.52mA
01 = 0.77mA
10 = 1.2mA
11 = 1.43mA
If AVDD
MICBIAS Current and Short Circuit
Detect Enable
0 = disabled
1 = enabled
MICBIAS Enable
0 = disabled
1 = enabled
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PP, Rev 3.1, August 2009
DESCRIPTION
1.8, values are scaled
1.8, values are scaled
Pre-Production
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