WM8729

Production Data

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PD Rev 4.1 June 2006

11

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

Mute DAC channels

1

Normal Operation

Floating

Enable IZD, MUTEB becomes an output to indicate when IZD occurs.

Table 2 Mute and Automute Control

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

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 10k

Ω 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.