WM9713LGEFLSLASHV datasheet(42/108 Pages) WOLFSON

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WM9713L

Pre-Production

PP Rev 3.0 June 2006

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

22h.

When

MBVOL=0,

MICBIAS=0.9*AVDD

and

when MBVOL=1,

MICBIAS=0.75*AVDD.

The microphone bias is driven to a dedicated MICBIAS pin 28 and is enabled by MPOP1EN in

22h.

When not in use the microphone bias can be powered down using the Powerdown register bit

MICBIAS (register 3Eh, bit 14).

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

MBOP2EN

0 (Off)

Microphone bias enable to GPIO8 (pin 12)

MBOP1EN

1 (On)

Microphone bias enable to MICBIAS (pin 28)

22h

MBVOL

Microphone bias voltage control

0: 0.9 * AVDD

1: 0.75 * AVDD

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.

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