WM8281ECSSLASHR datasheet(375/392 Pages) CIRRUS

375 / 392 page

WM8281

Rev 4.0

375

Digital microphone connection to the WM8281 is illustrated in Figure 86.

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

recommendations for the application microphone(s).

Digital Mic

MICVDD or

MICBIASn

AGND

Digital Mic

VDD

CLK

DATA

VDD

CLK

DATA

CHAN

VDD

DMICDATn

DMICCLKn

Digital

Microphone

Interface

Figure 86 Digital Microphone Connection

The MICBIAS generators can each operate as a voltage regulator or in bypass mode.

See “Charge

Pumps, Regulators and Voltage Reference

” for details of the MICBIAS generators.

In Regulator mode, the MICBIAS regulators are designed to operate without external decoupling

capacitors. The regulators can be configured to support a capacitive load if required (eg. for digital

microphone supply decoupling). The compatible load conditions

are detailed in the “Electrical

Characteristics

” section.

If the capacitive load on MICBIAS1, MICBIAS2 or MICBIAS3 exceeds the specified conditions for

Regulator mode (eg. due to a decoupling capacitor or long PCB trace), then the respective generator

must be configured in Bypass mode.

The maximum output current for each MICBIASn pin

is noted in the “Electrical Characteristics”. This

limit must be observed on each MICBIAS output, especially if more than one microphone is connected

to a single MICBIAS pin. Note that the maximum output current differs between Regulator mode and

Bypass mode. The MICBIAS output voltage can be adjusted using register control in Regulator mode.

HEADPHONE DRIVER OUTPUT PATH

The WM8281 provides 3 stereo headphone output drivers. These outputs are all ground-referenced,

allowing direct connection to the external load(s). There is no requirement for DC blocking capacitors.

In single-ended (default) configuration, the headphone outputs comprise 6 independently controlled

output channels, for up to 3 stereo headphone or line outputs. In mono (BTL) mode, the headphone

drivers support up to 3 differential outputs, suitable for a mono earpiece or hearing coil load.

The headphone outputs incorporate a common mode, or ground loop, feedback path which provides

rejection of system-related ground noise. The feedback pins must be connected to ground for normal

operation of the headphone outputs. A separate feedback path is provided for each of the stereo

headphone outputs. The HPOUT1 feedback is supported on two pins - the applicable pin is selected

using the ACCDET_SRC register bit.

The feedback pins should be connected to GND close to the respective headphone jack, as illustrated

in Figure 87. In mono (differential) mode, the feedback pin(s) should be connected to the ground

plane that is physically closest to the earpiece output PCB tracks.

It is recommended to ensure that the electrical characteristics of the PCB traces for each output pair

are closely matched. This is particularly important to matching the two traces of a differential (BTL)

output.

WM8281ECS/R Datenblatt(PDF) 375 Page - Cirrus Logic

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