WM8281ECSSLASHR datasheet(373/392 Pages) CIRRUS

373 / 392 page

WM8281

Rev 4.0

373

APPLICATIONS INFORMATION

RECOMMENDED EXTERNAL COMPONENTS

ANALOGUE INPUT PATHS

The WM8281 provides up to 6 analogue audio input paths. Each of these inputs is referenced to the

internal DC reference, VMID. A DC blocking capacitor is required for each analogue input pin used in

the target application. The choice of capacitor is determined by the filter that is formed between that

capacitor and the impedance of the input pin. The circuit is illustrated in Figure 83.

PGA

Input

Fc = high pass 3dB cut-off frequency

Fc =

2 RC

VMID

Figure 83 Audio Input Path DC Blocking Capacitor

In accordance with the WM8281

input pin resistance (see “Electrical Characteristics”), it is

recommended that a 1

F capacitance for all input connections will give good results in most cases,

with a 3dB cut-off frequency around 13Hz.

Ceramic capacitors are suitable, but care must be taken to ensure the desired capacitance is

maintained at the AVDD operating voltage. Also, ceramic capacitors may show microphonic effects,

where vibrations and mechanical conditions give rise to electrical signals. This is particularly

problematic for microphone input paths where a large signal gain is required.

A single capacitor is required for a single-ended line or microphone input connection. For a differential

input connection, a DC blocking capacitor is required on both input pins.

The external connections for single-ended and differential microphones, incorporating the WM8281

microphone bias circuit, are shown

later in the “Microphone Bias Circuit” section - see Figure 84.

DIGITAL MICROPHONE INPUT PATHS

The WM8281 provides up to 8 digital microphone input paths; two channels of audio data can be

multiplexed on each of the DMICDATn pins. Each of these stereo pairs is clocked using the

respective DMICCLKn pin.

The external connections for digital microphones, incorporating the WM8281 microphone bias circuit,

are shown later in the “Microphone Bias Circuit” section - see Figure 86.

Ceramic decoupling capacitors for the digital microphones may be required - refer to the specific

recommendations for the application microphone(s).

When two microphones are connected to a single DMICDAT pin, the microphones must be configured

to ensure that the Left mic transmits a data bit when DMICCLK is high, and the Right mic transmits a

data bit when DMICCLK is low. The WM8281 samples the digital microphone data at the end of each

DMICCLK phase. Each microphone must tri-state its data output when the other microphone is

transmitting. Integrated pull-down resistors can be enabled on the DMICDAT pins if required.

The voltage reference for each digital microphone interface is selectable. It is important that the

selected reference for the WM8281 interface is compatible with the applicable configuration of the

external microphone.

WM8281ECS/R Datenblatt(PDF) 373 Page - Cirrus Logic

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