WM8734SEFL Wolfson Microelectronics, WM8734SEFL Datasheet - Page 18

• Manufacturer Part Number: WM8734SEFL
• Description: Audio CODECs Stereo CODEC
• Manufacturer: Wolfson Microelectronics

Specifications of WM8734SEFL

• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: QFN-28
• Minimum Operating Temperature: - 25 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

WM8734
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The line inputs are biased internally through the operational amplifier to VMID. Whenever the line
inputs are muted or the device placed into standby mode, the line inputs are kept biased to VMID
using special anti-thump circuitry. This reduces any audible clicks that may otherwise be heard when
re-activating the inputs.
The external components required to complete the line input application is shown in the Figure 9.
Figure 9 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 = 5K, R2 = 5K, C1 = 47pF, C2 = 470nF (10V npo ceramic type).
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 WM8734 and the driving audio equipment. C2 together with the input
impedance of the WM8734 form a high pass filter.
ADC
The WM8734 uses a multi-bit oversampled sigma-delta ADC. A single channel of the ADC is
illustrated in the Figure 10.
Figure 10 Multi-Bit Oversampling Sigma Delta ADC Schematic
AGND
FROM LINE INPUT
R1
R2
AGND
INTEGRATOR
ANALOG
AGND
C1
MULTI
BITS
C2
PD, Rev 4.3, January 2009
TO ADC DIGITAL FILTERS
LINEIN
Production Data
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