Datasheet
www.ti.com
SYSTEM CLOCK
SCKI
0.8 V
SCKI
2 V
t
w(SCKL)
t
w(SCKH)
T0005B07
FADE-IN AND FADE-OUT FUNCTIONS
PCM1808
SLES177A – APRIL 2006 – REVISED AUGUST 2006
The PCM1808 supports 256 f
S
, 384 f
S
and 512 f
S
as system clock, where f
S
is the audio sampling frequency.
The system clock must be supplied on SCKI (pin 6).
The PCM1808 has a system clock detection circuit which automatically senses if the system clock is operating
at 256 f
S
, 384 f
S
, or 512 f
S
in slave mode. In master mode, the system clock frequency must be controlled
through the serial control port, which uses MD1 (pin 111) and MD0 (pin 10). The system clock is divided down
automatically to generate frequencies of 128 f
S
and 64 f
S
, which are used to operate the digital filter and the
delta-sigma modulator, respectively.
Table 1 shows some typical relationships between sampling frequency and system clock frequency, and
Figure 17 shows system clock timing.
Table 1. Sampling Frequency and System Clock Frequency
SAMPLING FREQUENCY (kHz) SYSTEM CLOCK FREQUENCY (f
SCLK
) (MHz)
256 f
S
384 f
S
512 f
S
8 2.048 3.072 4.096
16 4.096 6.144 8.192
32 8.192 12.288 16.384
44.1 11.2896 16.9344 22.5792
48 12.288 18.432 24.576
64 16.384 24.576 32.768
88.2 22.5792 33.8688 45.1584
96 24.576 36.864 49.152
SYMBOL PARAMETER MIN MAX UNIT
t
w(SCKH)
System clock pulse duration, HIGH 8 ns
t
w(SCKL)
System clock pulse duration, LOW 8 ns
System clock duty cycle 40% 60%
Figure 17. System Clock Timing
The PCM1808 has fade-in and fade-out functions on DOUT (pin 9) to avoid pop noise, and the functions come
into operation in some cases as described in several following sections. The level changes from 0 dB to mute or
mute to 0 dB are performed using calculated pseudo S-shaped characteristics with zero-cross detection.
Because of the zero-cross detection, the time needed for the fade in and fade out depends on the analog input
frequency (f
in
). It takes 48/f
in
until processing is completed. If there is no zero cross during 8192/f
S
, DOUT is
faded in or out by force during 48/f
S
(TIME OUT). Figure 18 illustrates the fade-in and fade-out operation
processing.
11
Submit Documentation Feedback