WM8281ECSSLASHR datasheet(207/392 Pages) CIRRUS

207 / 392 page

WM8281

Rev 4.0

207

In applications where a large decoupling capacitance is present on the MICBIAS output, the MICDET

Clamp function alone may be unable to discharge the capacitor sufficiently to eliminate pops and

clicks associated with jack insertion and removal. In this case, it may be desirable to use the General

Purpose Switch within the WM8281 to provide isolation from the MICBIAS output; an example circuit

is shown in Figure 64.

The General Purpose Switch is configured using SW1_MODE. This register allows the switch to be

disabled, enabled, or synchronised to the MICDET Clamp status, as described in Table 76.

For jack pop suppression, it is recommended to set SW1_MODE=11. In this case, the switch contacts

are open whenever the MICDET Clamp is active, and the switch contacts are closed whenever the

MICDET Clamp is inactive.

Normal accessory functions are supported when the switch contacts (GPSWA and GPSWB) are

closed, and the MICDET Clamp is inactive. Ground clamping of MICDET, and isolation of MICBIAS

are achieved when the switch contacts are open, and the MICDET Clamp is active.

Note that the MICDET Clamp function must also be configured appropriately when using this method

of pop suppression control.

HPOUT1FB1/

MICDET2

MICDET1/

HPOUT1FB2

MICBIASn

* INnRP

R1+R2 = 2.2k

 (+/-2%)

GPSWA

GPSWB

* Note: The Jack plug is shown partially

removed, with the MICDET1 pin in

contact with the headphone load.

* see note

General Purpose

Switch Control

SW1_MODE

WM8281

MICDET

Clamp Control

MICD_CLAMP_MODE

MICD_CLAMP_STS

MICD_CLAMP_DB

When the MICDET Clamp is active in the configuration shown, the

MICDET1 pin is grounded via the headphone jack ground connection.

* Note that the Right analogue mic

channel is recommended with the

external accessory detect function

Figure 64 General Purpose Switch circuit

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