STAC9721 datasheet(33/48 Pages) ETC1

33 / 48 page

SigmaTel, Inc.

Data Sheet

STAC9721

04/07/00

8. EXTENDED CODEC FUNCTIONALITY

8.1 Anti-Pop Circuitry

The STAC9721/23 provides an integrated output signal (APOP on pin 34) to aid in low-component-count

anti-pop implementations. An audible speaker "pop" can occur when the main power is applied to, or

removed from, the codec or audio output amplifier. In ac coupled systems, the speaker sided of the ac

coupling capacitor is shunted to ground through a transistor or FET; this prevents audible pops when the

system is powering on and off. A 10

µF capacitor on CAP1 provides a delay to hold-off power to the

output stages on power up. A 22

µF capacitor provides reserve power to sustain the output shunting

action until the power has been fully removed on power down. APOP is active logic high during shunting

operations; APOP is at logic low during normal operations.

9. AC TIMING CHARACTERISTICS (Tambient = 25 °C, AVdd = DVdd = 5.0V or 3.3V ± 5%,

AVss=DVss+0V; 50pF external load)

9.1 Cold Reset

Figure 13. Cold Reset

RESET#

BIT_CLK

Tres_low

Trst2clk

Table 23. Cold Reset

Parameter

Symbol

Min

Typ

Max

Units

RESET# active low pulse width

Tres_low

1.0

RESET# inactive to BIT_CLK startup delay

Trst2clk

162.8

# denotes active low.

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