Texas Instruments PCM4222EVM, User Manual

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2.5 Master Clock Source
Hardware Configuration
The PCM4222 and the DIT4192 transmitters require a master clock source for operation. The master
clock can be generated using one of two crystal oscillators (designated as X1 or X2), or from an external
clock source connected at the BNC input connector J11. The clock generated by the crystal oscillators or
external source is used directly by the DIT4192 transmitters. However, this clock must be divided by two
when used by the PCM4222. A D-type flip-flop (U21) performs this function.
Oscillator X1 is fixed at 22.5792MHz, and may provide the master clock for 44.1kHz and related sampling
rates, including 88.2kHz and 176.4kHz. Oscillator X2 is fixed at 24.576MHz, and may provide the master
clock for 48kHz and related sampling rates, including 96kHz and 192kHz.
An external clock source (EXT CLOCK), may be input at BNC connector J11 and is buffered by U19. The
buffer includes a tri-state output, so that it may be disabled when one of the crystal oscillators is used as
the master clock source. Buffer U19 is always operated from the +3.3V supply generated by voltage
regulator U22, and is tolerant to +5V input logic levels. The maximum external master clock frequency is
27.648MHz.
Table 3 summarizes the master clock source selection using switch SW6. Note that the user should not
enable oscillators X1 and X2 simultaneously, because it will result in output contention and improper
operation.
Table 4 lists the master clock rate requirements for commonly used digital audio sampling
rates.
Table 3. Master Clock Source Selection
Switch SW6,
EXTCLK Switch SW6, X2 Switch SW6, X1 Master Clock Selection
LO LO LO External Clock connected at BNC input J11
HI LO HI Oscillator X1, 22.5792MHz
±
50ppm
HI HI LO Oscillator X2, 24.576MHz
±
50ppm
HI HI HI Not allowed due to oscillator output contention
Table 4. Master Clock Frequencies for Common Output Sampling and Data Rates
EVM Master Clock Rate PCM4222 MCKI Clock Rate
PCM4222 Output Mode Output Rate (MHz) (MHz)
8kHz 4.096 2.048
32kHz 16.384 8.192
PCM Normal
44.1kHz 22.5792 11.2896
48kHz 24.576 12.288
88.2kHz 22.5792 11.2896
PCM Double Speed
96kHz 24.576 12.288
176.4kHz 22.5792 11.2896
PCM Quad Speed
192kHz 24.576 12.288
DSD, 64x Oversampling 2.8224MHz 22.5792 11.2896
DSD, 128x Oversampling 5.6448MHz 22.5792 11.2896
Multi-Bit Modulator 6.144MHz 24.576 12.288
SBAU124 – December 2006 PCM4222EVM User's Guide 9
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