WM8940CGEFLSLASHV datasheet(48/88 Pages) CIRRUS

48 / 88 page

WM8940

Rev 4.4

UNUSED ANALOGUE INPUTS/OUTPUTS

Whenever an analogue input/output is disabled, it remains connected to AVDD/2 through a resistor.

This helps to prevent pop noise when the output is re-enabled. The resistance between the voltage

buffer and the output pins can be controlled using the VROI control bit. The default impedance is low,

so that any capacitors on the outputs can charge up quickly at start-up. If a high impedance is desired

for disabled outputs, VROI can then be set to 1, increasing the resistance to about 30k

.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R49

VROI

VREF (AVDD/2) to analogue output

resistance

0: approx 1k



1: approx 30 k



Table 39 Disabled Outputs to VREF Resistance

A dedicated buffer is available for tying off unused analogue I/O pins as shown in Figure 21. This

buffer can be enabled using the BUFIOEN register bit.

Table 40 summarises the tie-off options for the speaker and mono output pins.

AVDD/2

Used to tie off all unused

inputs and outputs

BUFIOEN

R1[2]

SPKOUTP

SPKOUTN

MONOOUT

30k

VROI

R49[0]

30k

VROI

R49[0]

30k

VROI

R49[0]

Figure 21 Unused Input/Output Pin Tie-off Buffers

MONOEN/

SPKN/PEN

VROI

OUTPUT CONFIGURATION

Ω tieoff to AVDD/2

30k

Ω tieoff to AVDD/2

Output enabled (DC level=AVDD/2)

Table 40 Unused Output Pin Tie-off Options

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