DS1113F1
31
CS4399
4.6 Clock Output and Fractional-N PLL
Further restrictions are listed in
Figure 4-13. MCLK Source Switching
A source to MCLK_INT, either the XTAL (or external MCLK), the PLL, or the RCO, must be provided as long as the
CS4399 is operating; otherwise, the CS4399 enters a nonresponsive state, and I
2
C SDA signal can be held low. The only
way to recover from this nonresponsive state is either through a reset or a POR event. Switching MCLK sources during
DAC operation causes audible artifacts, but does not put the device in an unrecoverable state. In an MCLK
source-switching event, the intended clock source must be present and ready before switching occurs.
After POR or reset event, RCO is selected as default source of MCLK_INT.
4.5.1.1 Internal RC Oscillator
As described in
, the CS4399 includes an internal RC oscillator that can be used as a clock source for
peripheral circuit such as control port or charge pump.
4.6 Clock Output and Fractional-N PLL
The CS4399 clock output can be used as a master clock for other data-conversion or signal-processing components,
which requires synchronous timing to the CS4399.
Table 4-3. MCLK Source Restrictions
Internal
MCLK
Source
MCLK_SRC_SEL MCLK_INT
Restrictions
Direct MCLK
or XTAL
00
0
• Nominal MCLK_INT frequency = 24.576 MHz
• All specified CLKOUT frequencies (generated by PLL or XTAL) are supported
• CLKOUT outputs (/2, /3, /4, /8 divide) optionally
1
• Nominal MCLK_INT frequency = 22.5792 MHz
• All specified CLKOUT frequencies (generated by PLL or XTAL) are supported
• CLKOUT outputs (/2, /3, /4, /8 divide) optionally
PLL
01
0
• Nominal MCLK_INT frequency = 24.576 MHz
• PDN_PLL = 0 and PLL properly configured to generate 24.576 MHz given reference input
frequency on XTI/MCLK pin
• Only MCLK_INT on CLKOUT is supported on CLKOUT pin
• CLKOUT outputs (/2, /3, /4, /8 divide) optionally
1
• Nominal MCLK_INT frequency = 22.5792MHz
• PDN_PLL = 0 and PLL properly configured to generate 22.5792 MHz given reference input
frequency on XTI/MCLK pin
• Only MCLK_INT on CLKOUT is supported on CLKOUT pin
• CLKOUT outputs (/2, /3, /4, /8 divide) optionally
Internal
PLL
XTI/MCLK
Internal MCLK
CLKOUT
÷