Unused Analogue Inputs/Outputs - Cirrus Logic WM8940 Manual

48

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.
REGISTER BIT LABEL
ADDRESS
R49 0 VROI
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
AVDD/2 +
BUFIOEN
R1[2]
Used to tie off all unused
inputs and outputs
Figure 21 Unused Input/Output Pin Tie-off Buffers
MONOEN/ VROI
SPKN/PEN
0 0
0 1
1 X
Table 40 Unused Output Pin Tie-off Options
DEFAULT
0 VREF (AVDD/2) to analogue output
resistance
0: approx 1k
1: approx 30 k
1k
MONOOUT
30k
VROI
R49[0]
1k
SPKOUTP
30k
VROI
R49[0]
1k
SPKOUTN
30k
VROI
R49[0]
OUTPUT CONFIGURATION
1kΩ tieoff to AVDD/2
30kΩ tieoff to AVDD/2
Output enabled (DC level=AVDD/2)
WM8940
DESCRIPTION
Rev 4.4