wm9714l Wolfson Microelectronics plc, wm9714l Datasheet - Page 47

• Manufacturer Part Number: wm9714l
• Description: Ac?97 Audio Codec
• Manufacturer: Wolfson Microelectronics plc

Pre-Production
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MICROPHONE BIASING CIRCUIT
The MICBIAS output provides a low noise reference voltage suitable for biasing electret type
microphones and the associated external resistor biasing network. Refer to the Applications
Information section for recommended external components. The MICBIAS voltage can be altered via
MBVOL in register 22h.
MICBIAS=0.75*AVDD.
The microphone bias is driven to a dedicated MICBIAS pin 28 and is enabled by MPOP1EN in
register 22h. It can also be configured to drive out on GPIO8 pin 12 enabled by MPOP2EN in register
22h.
When not in use the microphone bias can be powered down using the Powerdown register bit
MICBIAS (register 3Eh, bit 14).
Table 24 Microphone Bias Voltage Control
The internal MICBIAS circuitry is shown in Figure 22. Note that the maximum source current
capability for MICBIAS is 3mA. The external biasing resistors therefore must be large enough to limit
the MICBIAS current to 3mA.
Figure 22 Microphone Bias Schematic
22h
REGISTER
ADDRESS
7
6
5
BIT
MBOP2EN
MBOP1EN
MBVOL
LABEL
When MBVOL=0, MICBIAS=0.9*AVDD and when MBVOL=1,
0 (Off)
1 (On)
0
DEFAULT
MICBIAS Output 2 Enable Control
1 = Enable MICBIAS output on GPIO8 (pin
12)
0 = Disable MICBIAS output on GPIO8 (pin
12)
MICBIAS Output 1 Enable Control
1 = Enable MICBIAS output on MICBIAS
(pin 28)
0 = Disable MICBIAS output on MICBIAS
(pin 28)
MICBIAS Output Voltage Control
1 = 0.75 x AVDD
0 = 0.9 x AVDD
DESCRIPTION
PP, Rev 3.2, October 2008
WM9714L
47