PCM1774 datasheet(12/49 Pages) TI

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DESCRIPTION OF OPERATION

System Clock Input

w(SCKH)

SCKI

w(SCKL)

0.7V

0.3V

T0005-12

Power-On Reset and System Reset

Power On/Off Sequence

PCM1774

SLAS551 – JULY 2007

The PCM1774 can accept clocks of various frequencies without a PLL. They are used for clocking the digital

filters and automatic level control and delta-sigma modulators and are classified as common-audio and

application-specific clocks. Table 2 shows frequencies of the common-audio clock and application-specific clock.

Figure 13 shows the timing requirements for system clock inputs. The sampling rate and frequency of the

system clocks are determined by the settings of register 86 (MSR[2:0]) and register 85 (NPR[5:0]). Note that the

sampling rate of the application-specific clock has a little sampling error. The details are shown in Table 9.

Table 2. System Clock Frequencies

CLOCK

FREQUENCIES

Common-audio clock

11.2896, 12.288, 16.9344, 18.432 MHz

Application-specific clock

12, 13, 13.5, 24, 26, 27, 19.2, 19.68, 38.4, 39.36 MHz

PARAMETERS

SYMBOL

MIN

UNITS

System-clock pulse duration, high

tw(SCKH)

System-clock pulse duration, low

tw(SCKL)

Figure 13. System Clock Timing

The power-on-reset circuit outputs a reset signal, typically at VDD = 1.2 V, and this circuit does not depend on

the voltage of other power supplies (VCC, VPA, and VIO). Internal circuits are cleared to default status, then all

analog and digital outputs have no signal. The PCM1774 does not require any power supply sequencing. Set

System reset is enabled by setting register 85 (SRST = 1). After the reset sequence, the register data is reset to

SRST = 0 automatically. All circuits are cleared to their default status at once by the system reset. Note that the

PCM1774 has audible pop noise on the analog outputs when enabling SRST.

To reduce audible pop noise, a sequence of register settings is required after turning all power supplies on when

powering up, or before turning the power supplies off when powering down. If some modules are not required for

a particular application or operation, they should be placed in the power-down state after performing the

power-on sequence. The recommended power-on and power-off sequences are shown in Table 3 and Table 4,

respectively.

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