WM8756 datasheet(20/39 Pages) WOLFSON

20 / 39 page

WM8756

Advance Information

AI Rev 1.3 October 2001

With IZD enabled, applying MUTE for 1024 consecutive input samples will cause all outputs to be

connected directly to VCAP. Additionally, if 2048 consecutive zero input samples are applied to all 6

channels, and IZD=0, internal analogue mute will be applied. It will be removed as soon as any channel

receives a non-zero input.

The MUTE pin can be used as an input. In this case it performs the same function as the MUTE register

bit. Driving the MUTE pin high will apply a 'soft' mute. Driving it low again, will remove the MUTE

immediately. Note that this hardware mute feature doesn't require the MODE pin to be set high.

MUTE PIN

DESCRIPTION

Normal Operation

Mute all DAC channels

floating

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

A diagram showing how the various Mute modes interact is shown below in Figure 13.

IZD (Register Bit)

AUTOMUTED

(Internal Signal)

10k

Ω

MU (Register Bit)

SOFTMUTE

(Internal

Signal)

MUTE

Figure 13 Selection Logic for MUTE Modes

The MUTE pin behaves as a bi-directional function, that is, as an input to select MUTE or NOT-MUTE, or

as an output indication of automute operation. MUTE is active high; taking the pin high causes the filters

to soft mute, ramping down the audio signal over a few milliseconds. Taking MUTE low again allows data

into the filter.

The automute function detects a series of zero value audio samples of 1024 samples long being applied

to all 6 channels. After such an event, a latch is set whose output (AUTOMUTED) is wire OR’ed through a

10kohm resistor to the MUTE pin. Thus if the MUTE pin is not being driven, the automute function will

assert MUTE.

If MUTE is tied low, AUTOMUTED is overridden and will not mute. If MUTE is driven from a source

follower, or diode, then both MUTE and automute functions are available. If MUTE is not driven,

AUTOMUTED appears as a weak output (10k source impedance) so can be used to drive external mute

circuits. The automute signal is AND’ed with IZD, this qualified mute signal then being OR’ed into the

SOFTMUTE control. Therefore, in software mode, automute operation may be controlled with IZD control

bit.

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