WM8731LSEFL Wolfson Microelectronics, WM8731LSEFL Datasheet - Page 23

• Manufacturer Part Number: WM8731LSEFL
• Description: Audio CODECs Stereo Codec with H/P
• Manufacturer: Wolfson Microelectronics

Specifications of WM8731LSEFL

• Number Of Adc Inputs: 1
• Number Of Dac Outputs: 1
• Conversion Rate: 96 KSPS
• Interface Type: Serial (2-Wire, 3-Wire, I2S)
• Resolution: 18 bit, 20 bit
• Operating Supply Voltage: - 0.3 V to + 3.63 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: QFN EP
• Minimum Operating Temperature: - 40 C
• Number Of Channels: 2 ADC/2 DAC
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

WM8731 / WM8731L
w
Figure 11 Line Input Application Drawing
For interfacing to a typical CD system, it is recommended that the input is scaled to ensure that there
is no clipping of the signal. R1 = 5.6k, R2 = 5.6k, C1 = 220pF, C2 = 1μF.
R1 and R2 form a resistive divider to attenuate the 2 Vrms output from a CD player to a 1 Vrms level,
so avoiding overloading the inputs. R2 also provides a discharge path for C2, thus preventing the
input to C2 charging to an excessive voltage which may otherwise damage any equipment connected
that is not suitably protected against high voltages. C1 forms an RF low pass filter for increasing the
rejection of RF interference picked up on any cables. C2 forms a DC blocking capacitor to remove
the DC path between the WM8731/L and the driving audio equipment. C2 together with the input
impedance of the WM8731/L form a high pass filter.
MICROPHONE INPUT
MICIN is a high impedance, low capacitance input suitable for connection to a wide range of
monophonic microphones of different dynamics and sensitivities.
The MICIN includes programmable volume adjustments and a mute function. The scheme is shown
in Figure 12. Passive RF and active Anti-Alias filters are also incorporated within the microphone
inputs. These allow a matched interface to the multi-bit oversampling ADC and preventing high
frequencies aliasing into the audio band or otherwise degrading performance.
Figure 12 Microphone Input Schematic
There are 2 stages of gain made up of two low noise inverting operational amplifiers.
The 1
series with MICIN the gain of stage can be adjusted. For example adding Rmic = 40K sets the gain
of stage 1 to x1 (0dB). The equation below can be used to calculate the gain versus Rmic.
AGND
st
MICIN
stage comprises a nominal gain of G1 = 50k/10k = 5. By adding an external resistor (Rmic) in
G1 = 50k/ (Rmic + 10k)
10k
R1
VMID
R2
50k
AGND
AGND
20dB GAIN BOOST
VMID
C1
C2
PD, Rev 4.8, April 2009
LINEIN
Production Data
ADC
To
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