Rainbow-electronics AT73C246 Bedienungsanleitung PDF herunterladen (Seite 60)

11050A–PMAAC–07-Apr-10

AT73C246

500ms timeout. Contrary to the first point, which has no timeout, the audio power-off time

limit is here fixed to 500ms. Beyond this limit, the codec is hardly reseted as in the following

point.

• PMU Power-fail event. In this case, the PMU finite state machine makes an immediate hard

reset of the audio codec to ensure fast shutdown. This case may generate an audible click /

pop noise.

12.4.1.6 Power-off Time

At power-off, the audio controller needs to perform several controls on audio codec sub-func-

tions and to discharge the output coupling capacitors. Therefore, the codec’s power-off time is

divided into:

• a digital power-off time and,

• an analogue one.

During this power-off phase, the codec‘s master clock and supply must be present. See “Audio

Codec Power-off Waveforms” on page 60.

Figure 12-6. Audio Codec Power-off Waveforms

The digital power-off time depends on the number of controls (power-off, gain steps ramping, ...)

to perform and for this reason strongly varies according to:

• the master clock frequency,

• the current path,

• the current gains and

• the current Automatic Soft Ramping time (ASR_TIME in AUDIO_CONTROL(0x11)).

In worst case conditions (slowest clock, maximum ASR_TIME, maximum complexity audio path,

maximum gains everywhere), the power-off time reaches 3 seconds. During this period, the

VDD4

VMID

AUDIO

SIGNAL

ENAC

digital

power-o

time

analog

power-o

time

MCLK

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Rainbow-electronics AT73C246 Bedienungsanleitung Seite 60