WM8972LEFLSLASHR datasheet(45/49 Pages) WOLFSON

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Preliminary Technical Data

WM8972L

PTD Rev 2.2 June 2004

COMPONENT

REFERENCE

SUGGESTED

VALUE

DESCRIPTION

C1 – C4

100nF

De-coupling for DBVDD, DCVDD, AVDD, OPVDD

C5 – C6

10uF

Reservoir capacitor for DVDD, AVDD. Should the supplies use separate sources then

additional capacitors will be required of each additional source.

C7 – C10

1uF

AC input coupling capacitors

C11

2.2uF

Output AC coupling capacitors to remove DC level from MONOOUT

C12

100nF

De-coupling for VMID.

C13

10uF

Reservoir capacitor for VMID

C14

100nF

De-coupling for VREF

C15

10uF

Reservoir capacitor for VREF

C16

100nF

De-coupling for MICBIAS – Not required if MICBIAS output is not used

C17

10uF

Reservoir capacitor for MICBIAS – Not required if MICBIAS output is not used

Table 36 External Components Descriptions

Note:

For Capacitors C5, C6, C13, C15 and C17 it is recommended that very low ESR components are used.

LINE INPUT CONFIGURATION

When INPUT1+/INPUT1- or INPUT2+/INPUT2- are used as line inputs, the microphone boost and

ALC functions should normally be disabled.

In order to avoid clipping, the user must ensure that the input signal does not exceed AVDD. This

may require a potential divider circuit in some applications. It is also recommended to remove RF

interference picked up on any cables using a simple first-order RC filter, as high-frequency

components in the input signal may otherwise cause aliasing distortion in the audio band. AC signals

with no DC bias should be fed to the WM8972L through a DC blocking capacitor, e.g. 1

µF.

MICROPHONE INPUT CONFIGURATION

Figure 44 Recommended Circuit for Line Input

For interfacing to a microphone, the ALC function should be enabled and the microphone boost

switched on. Microphones held close to a speaker’s mouth would normally use the 13dB gain setting,

while tabletop or room microphones would need a 29dB boost.

The recommended application circuit is shown above. R1 and R2 form part of the biasing network

(refer to Microphone Bias section). R1 connected to MICBIAS is necessary only for electret type

microphones that require a voltage bias. R2 should always be present to prevent the microphone

input from charging to a high voltage which may damage the microphone on connection. R1 and R2

should be large so as not to attenuate the signal from the microphone, which can have source

impedance greater than 2kOhm. C1 together with the source impedance of the microphone and the

WM8972L input impedance forms an RF filter. C2 is a DC blocking capacitor to allow the microphone

to be biased at a different DC voltage to the MICIN signal.

47kOhm

220pF

1uF

AGND

INPUT1+/-

INPUT2+/-

FROM

MICROPHONE

680 Ohm to 2.2kOhm

check microphone's specification

MICBIAS

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