wm8953 Wolfson Microelectronics plc, wm8953 Datasheet - Page 29

• Manufacturer Part Number: wm8953
• Description: Low Power Stereo Adc With Pll And Tdm Interface Low Power Stereo Adc With Pll And Tdm Interface
• Manufacturer: Wolfson Microelectronics plc

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Production Data
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.
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.
Table 5 Disabled Input/Output Control
REGISTER
ADDRESS
R1 (01h)
R58 (3Ah)
R57 (39h)
Anti-Pop
REGISTER
ADDRESS
4
0
BIT
3
BIT
MICBIAS_ENA
(rw)
MBSEL
BUFIOEN
LABEL
LABEL
0b
DEFAULT
DEFAULT
0b
0b
Microphone Bias
0 = OFF (high impedance output)
1 = ON
Microphone Bias Voltage Control
0 = 0.9 * AVDD
1 = 0.65 * AVDD
Enables the Buffered VMID reference at
disabled inputs
0 = Disabled
1 = Enabled
DESCRIPTION
DESCRIPTION
PD, January 2009, Rev 4.0
WM8953
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