WM8950GEFLSLASHV datasheet(17/52 Pages) WOLFSON

17 / 52 page

Preliminary Technical Data

WM8950

PTD Rev 2.1 June 2005

The BOOST stage is enabled under control of the BOOSTEN register bit.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

Power

management 2

BOOSTEN

Input BOOST enable

0 = Boost stage OFF

1 = Boost stage ON

Table 5 Input BOOST Enable Control

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

the MBVSEL register bit.

When MBVSEL=0, MICBIAS=0.9*AVDD and when MBVSEL=1,

MICBIAS=0.75*AVDD. The output can be enabled or disabled using the MICBEN control bit.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

Power

management 1

MICBEN

Microphone Bias Enable

0 = OFF (high impedance output)

1 = ON

Table 6 Microphone Bias Enable

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R44

Input Control

MBVSEL

Microphone Bias Voltage Control

0 = 0.9 * AVDD

1 = 0.75 * AVDD

Table 7 Microphone Bias Voltage Control

The internal MICBIAS circuitry is shown in Figure 9.

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.

AGND

MBVSEL=0

MICBIAS

= 1.8 x VMID

= 0.9 X AVDD

VMID

internal

resistor

internal

resistor

MBVSEL=1

MICBIAS

= 1.5 x VMID

= 0.75 X AVDD

Figure 9 Microphone Bias Schematic

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