WM8953ECSSLASHRV datasheet(29/100 Pages) WOLFSON

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Production Data

WM8953

PD, January 2009, Rev 4.0

MICROPHONE BIAS CONTROL

The MICBIAS output provides a low noise reference voltage suitable for biasing electret type

microphones via an external resistor. Refer to the Applications Information section for recommended

external components. The MICBIAS voltage can be enabled or disabled using the MICBIAS_ENA

control bit and the voltage can be selected using the MBSEL register bit as detailed in Table 4.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R1 (01h)

MICBIAS_ENA

(rw)

Microphone Bias

0 = OFF (high impedance output)

1 = ON

R58 (3Ah)

MBSEL

Microphone Bias Voltage Control

0 = 0.9 * AVDD

1 = 0.65 * AVDD

Table 4 Microphone Bias Control

Note that the maximum source current capability for MICBIAS is 3mA. The external biasing

resistance must be large enough to limit the MICBIAS current to 3mA.

MICROPHONE CURRENT DETECT

A MICBIAS current detect function allows detection of accessories such as headset microphones.

When the MICBIAS load current exceeds one of two programmable thresholds, (e.g. short circuit

current or normal operating current), an interrupt or GPIO output can be generated. The current

detection circuit is enabled by the MCD bit; the current thresholds are selected by the MCDTHR and

MCDSCTH register fields as described in Table 24- see “General Purpose Input/Output” for a full

description of these fields.

DISABLED INPUT CONTROL

After start-up, it may be desirable to disable an input stage, in order to reduce power consumption on

an unused PGA or Input Mixer.

In order to avoid audible pops caused by a disabling any part of the input circuits, the WM8953 can

maintain the input at VMID even when the PGA or Input Mixer is disabled. This is achieved by

connecting a buffered VMID reference to the input. The buffered VMID is enabled by setting

BUFIOEN.

When BUFIOEN is enabled, the WM8953 maintains the charge on the input capacitors connected to

any disabled input amplifier. This suppresses the audible artefacts that would otherwise arise when

an input amplifier is disabled or enabled. In some applications, a pop generated at an input stage can

be entirely suppressed by correctly managing the output stages (eg. using the ADC mute). However,

it may be desirable to use the buffered VMID feature in order to eliminate the input PGA start-up

delay (the input capacitor charging time) in addition to suppressing any mute/un-mute pops. In

applications where frequent enabling and configuration of signal paths is used, it is recommended to

enable BUFIOEN at all times.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R57 (39h)

Anti-Pop

BUFIOEN

Enables the Buffered VMID reference at

disabled inputs

0 = Disabled

1 = Enabled

Table 5 Disabled Input/Output Control

WM8953ECS/RV 数据表(PDF) 29 Page - Wolfson Microelectronics plc

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