WM8720

Production Data

WOLFSON MICROELECTRONICS LTD

PD Rev 3.0 November 2000

10

IZD (Register Bit)

AUTOMUTED

(Internal Signal)

10k

Ω

MU (Register Bit)

SOFTMUTE

(Internal Signal)

MUTE

PIN

Figure 6 Mute Circuit Operation

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 both left and right 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, automute 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,

automute 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.

I

In hardware mode, pins 4 and 5 become input controls for selection of input data format type, and

input data word length, see Table 4. I

enough bit clocks are sent.

ML/I

MC/IWL – PIN 5

INPUT DATA MODE

0

0

16-bit normal

0

1

20-bit normal

1

0

24-bit normal

11

I

Table 4 Control of Input Data Format Type and Input Data Word Length

DM DE-EMPHASIS

In hardware mode, pin 6 becomes an input control for selection of de-emphasis filtering to be

applied. See Figure 8.

DM

0

De-emphasis off

DM

1

De-emphasis on

Table 5 De-emphasis Control

PWDN POWERDOWN CONTROL

In both hardware and software modes, this pin selects powerdown of the entire device when taken

high.

PWDN

0

Device powered up

PWDN

1

Device powered down

Table 6 Powerdown Control