WM8991 datasheet(44/174 Pages) WOLFSON

44 / 174 page

WM8991

Pre-Production

PP, May 2008, Rev 3.1

INPUT PGA CONFIGURATION

Each of the four Input PGAs can be configured in single-ended or pseudo-differential mode.

Single-ended microphone operation of an Input PGA is selected by connecting the input source to

the inverting PGA input. The non-inverting PGA input must be connected to VMID by setting the

appropriate register bits.

For pseudo-differential microphone operation, the inverting and non-inverting PGA inputs are both

connected to the input source and not to VMID.

For any line input or other connection not using the Input PGA, the appropriate PGA input should be

disconnected from the external pin and connected to VMID.

PGA inputs to the device pins as shown in Table 4. The maximum available attenuation on any of

these input paths is achieved using these bits to disable the input path to the applicable PGA.

When not enabled as analogue inputs or as General Purpose inputs, the input pins can be biased to

VREF via a 1k

Ω resistor by setting the BUFIOEN bit. See “Pop Suppression Control” for details.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

LMP4

LIN34 PGA Non-Inverting Input Select

0 = LIN4 not connected to PGA

1 = LIN4 connected to PGA

LMN3

LIN34 PGA Inverting Input Select

0 = LIN3 not connected to PGA

1 = LIN3 connected to PGA

LMP2

LIN12 PGA Non-Inverting Input Select

0 = LIN2 not connected to PGA

1 = LIN2 connected to PGA

LMN1

LIN12 PGA Inverting Input Select

0 = LIN1 not connected to PGA

1 = LIN1 connected to PGA

RMP4

RIN34 PGA Non-Inverting Input Select

0 = RIN4 not connected to PGA

1 = RIN4 connected to PGA

RMN3

RIN34 PGA Inverting Input Select

0 = RIN3 not connected to PGA

1 = RIN3 connected to PGA

RMP2

RIN12 PGA Non-Inverting Input Select

0 = RIN2 not connected to PGA

1 = RIN2 connected to PGA

R40 (28h)

RMN1

RIN12 PGA Inverting Input Select

0 = RIN1 not connected to PGA

1 = RIN1 connected to PGA

Table 4 Input PGA Configuration

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