WM9713L_06 WOLFSON [Wolfson Microelectronics plc], WM9713L_06 Datasheet - Page 42

• Manufacturer Part Number: WM9713L_06
• Description: AC 97 Audio + Touchpanel CODEC
• Manufacturer: WOLFSON [Wolfson Microelectronics plc]

WM9713L
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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 14. 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 14 Microphone Bias Schematic
MICBIAS CURRENT DETECT
The WM9713L includes a microphone bias current detect circuit with programmable thresholds for
the microphone bias current, above which an interrupt will be triggered. There are two separate
interrupt bits, MICDET to e.g. distinguish between one or two microphones connected to the
WM9713L, and MICSHT to detect a shorted microphone (mic button press). The microphone current
detect threshold is set by MCDTHR[2:0], for MICDET, and MCDSCTHR[1:0] for MICSHT.
Thresholds for each code are shown in Table 25
When not in use the microphone bias current detect circuit can be powered down using the
Powerdown register bit MCD (register 3Eh, bit 15).
See the GPIO and Interrupt Controller sections for details on the interrupt and status readback for
these MICBIAS current detection features.
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
0: 0.9 * AVDD
1: 0.75 * AVDD
Microphone bias enable to GPIO8 (pin 12)
Microphone bias enable to MICBIAS (pin 28)
Microphone bias voltage control
DESCRIPTION
PP Rev 3.0 June 2006
Pre-Production
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