Datasheet

GENERAL DESCRIPTION
SYSTEM CLOCK AND RESET FUNCTIONS
System Clock Input
t
(SCKH)
SystemClock
(SCK)
t
(SCKL)
2V
0.8V
High
Low
t
(SCY)
PCM1795
www.ti.com ........................................................................................................................................................................................................ SLES248 – MAY 2009
The PCM1795 requires a system clock to operate the digital interpolation filters and advanced segment DAC
modulators. The system clock is applied at the SCK input (pin 7). The PCM1795 has a system clock detection
circuit that automatically senses the frequency at which the system clock is operating. Table 2 shows examples
of system clock frequencies for common audio sampling rates. If the oversampling rate of the delta-sigma ( Δ Σ )
modulator is selected as 128 f
S
, the system clock frequency is required to be greater than 256 f
S
.
Figure 34 and Table 3 show the timing requirements for the system clock input. For optimal performance, it is
important to use a clock source with low phase jitter and noise. The Texas Instruments PLL1700 family of
multiclock generators is an excellent choice to provide the PCM1795 system clock.
Table 2. System Clock Rates for Common Audio Sampling Frequencies
SYSTEM CLOCK FREQUENCY (f
SCK
) (MHz)
SAMPLING FREQUENCY
(kHz) 128 f
S
192 f
S
256 f
S
384 f
S
512 f
S
768 f
S
32 4.096
(1)
6.144
(1)
8.192 12.288 16.384 24.576
44.1 5.6488
(1)
8.4672 11.2896 16.9344 22.5792 33.8688
48 6.144
(1)
9.216 12.288 18.432 24.576 36.864
96 12.288 18.432 24.576 36.864 49.152
(1)
73.728
(1)
192 24.576 36.864 49.152
(1)
73.728
(1)
X
(2)
X
(2)
(1) This system clock rate is not supported in I
2
C fast mode.
(2) This system clock rate is not supported for the given sampling frequency.
Figure 34. System Clock Input Timing
Table 3. Timing Characteristics for Figure 34
PARAMETER MIN MAX UNIT
t
(SCY)
System clock pulse cycle time 13 ns
t
(SCKH)
System clock pulse duration, high 0.4t
(SCY)
ns
t
(SCKL)
System clock pulse duration, low 0.4t
(SCY)
ns
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Product Folder Link(s): PCM1795