WM8729
Production Data
HARDWARE CONTROL MODES
The WM8729 is hardware programmable providing the user with options to select input audio data
format, de-emphasis and mute.
MUTE AND AUTOMUTE OPERATION
Pin 14 (MUTEB) controls selection of MUTE directly, and can be used to enable and disable the
automute function, or as an output of the automuted signal.
MUTEB PIN
DESCRIPTION
0
1
Mute DAC channels
Normal Operation
Floating
Enable IZD, MUTEB becomes an output to indicate when IZD occurs.
Table 2 Mute and Automute Control
1.5
1
0.5
0
-0.5
-1
-1.5
-2
-2.5
0
0.001
0.002
0.003
0.004
0.005
0.006
Time(s)
Figure 5 Application and Release of MUTEB
The MUTEB pin is an input to select mute or not mute. MUTEB is active low; taking the pin low
causes the filters to soft mute, ramping down the audio signal over a few milliseconds. Taking
MUTEB high again allows data into the filter. Refer to Figure 5.
The Infinite Zero Detect (IZD) function detects a series of zero value audio samples of 1024
samples long being applied to both channels. After such an event, a latch is set whose output
(AUTOMUTED) is connected through a 10kΩ resistor to the MUTEB pin. Thus if the MUTEB pin
is not being driven, the automute function will assert mute.
If MUTEB is tied high, AUTOMUTED is overridden and will not mute. If MUTEB is driven from a
bi-directional source, then both MUTE and automute functions are available. If MUTEB is not
driven, AUTOMUTED appears as a weak output (10k source impedance) so can be used to drive
external mute circuits. AUTOMUTED will be removed as soon as any channel receives a non-zero
input.
A diagram showing how the various Mute modes interact is shown below in Figure 6.
PD Rev 4.1 June 2006
11
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
