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PCM1807PW Datasheet(PDF) 11 Page - Texas Instruments |
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PCM1807PW Datasheet(HTML) 11 Page - Texas Instruments |
11 / 33 page www.ti.com SYSTEM CLOCK SCKI 0.8 V SCKI 2 V tw(SCKL) tw(SCKH) T0005B07 FADE-IN AND FADE-OUT FUNCTIONS PCM1807 SLES147 – SEPTEMBER 2005 The PCM1807 supports 256 fS, 384 fS and 512 fS as system clock, where fS is the audio sampling frequency. The system clock must be supplied on SCKI (pin 6). The PCM1807 has a system clock detection circuit which automatically senses if the system clock is operating at 256 fS, 384 fS, or 512 fS in slave mode. In master mode, the system clock frequency must be controlled through the serial control port, which uses MD (pin 10), MC (pin 11), and MS (pin 12). The system clock is divided down automatically to generate frequencies of 128 fS and 64 fS, 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 (fSCLK) (MHz) 256 fS 384 fS 512 fS 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 tw(SCKH) System clock pulse duration, HIGH 8 ns tw(SCKL) System clock pulse duration, LOW 8 ns Figure 17. System Clock Timing The PCM1807 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 (fin). It takes 48/fin until processing is completed. If there is no zero cross during 8192/fS, DOUT is faded in or out by force during 48/fS (TIME OUT). Figure 18 illustrates the fade-in and fade-out operation processing. 11 |
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