Cirrus Logic CS8422 - Manual (Page 38)

38 DS692F2
CS8422
7.3 SRC Muting
The SDOUT pin sourced by the SRC (SDOUT1 or SDOUT2 in Software Mode, SDOUT1 in Hardware
Mode) is set to all zero output (full mute) immediately after the RST pin is set high. While the output from
the SRC becomes valid, SDOUT will be soft unmuted over a period of approximately 27488/Fsi while in in-
terpolation mode (Fsi < Fso) or 54976/Fso while in decimation mode (Fsi > Fso). When the output becomes
invalid the SRC’s SDOUT is immediately set to all zero output (hard muted). After all invalid states have
been cleared, the SRC will soft unmute SDOUT.
7.4 SRC Master Clock
The CS8422 can use the clock signal supplied through XTI-XTO, the PLL, or an internal ring oscillator as
its master clock (MCLK). If the SRC MCLK source is selected as being XTI-XTO, care must be taken to en-
sure that the SRC MCLK source does not exceed 33 MHz. If the SRC MCLK source exceeds 33 MHz, an
internal clock divider can be enabled to divide the SRC MCLK source by 2, allowing the use of higher fre-
quency clocks. See
Section 7.4.1 and Section 7.4.2 for more details.
If the SRC MCLK is applied through XTI then it can be supplied from a digital clock source, a crystal oscil-
lator, or a fundamental mode crystal. If XTO is not used, such as with a digital clock source or crystal oscil-
lator, XTO should be left unconnected or pulled low through a 20 k
 resistor to GND.
If a crystal in conjunction with the internal oscillator is used to supply the SRC MCLK, the crystal circuit
should be connected as shown in
Figure 20 . If VL < 2.5 Volts, it is recommended that the crystal attached
across XTI and XTO should be specified as operating with a load capacitance of 10pF (capacitors in
Figure 20 should be 20 pF). If VL
 2.5 Volts, it is recommended that the crystal attached across XTI and
XTO should be specified as operating with a series capacitance of at 20pF (capacitors in Figure 20 should
be at 40 pF). Please refer to the crystal manufacturer’s specifications for more information about external
capacitor recommendations.
If the PLL clock is selected as the SRC MCLK, the SRC MCLK will be synchronous to incoming AES3-com-
patible data or ISCLK. Unlike RMCK, the user does not control PLL clock’s relationship to the sampling rate
of incoming AES3-compatible data (Fsi), or ISCLK. See
Table 2 for the relationship between the Fsi or IS-
CLK/64, and the PLL clock.
The CS8422 has the ability to operate without a master clock input through XTI. This benefits the design by
not requiring extra external clock components (lowering production cost) and not requiring a master clock
to be routed to the CS8422, resulting in lowered noise contribution in the system. In this mode, an internal
Fsi (or ISCLK/64) PLL/Fsi
Fsi
 49 kHz
512
60 kHz
 Fsi  98 kHz 256
120 kHz
 Fsi
128
Table 2. PLL Clock Ratios
XTI XTO
C C
Figure 20. Typical Connection Diagram for Crystal Circuit