Rainbow Electronics AT73C246 - Manual (Page 60)

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-off
time
analog
power-off
time
MCLK