Datasheet
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DESCRIPTION OF OPERATION
System Clock Input
t
w(SCKH)
SCKI
t
w(SCKL)
0.7V
IO
0.3V
IO
T0005-12
Power-On Reset and System Reset
Power On/Off Sequence
PCM1870
SLAS544A – MAY 2007 – REVISED SEPTEMBER 2007
The PCM1870 can accept input clocks of various frequencies without a PLL. The clocks are used for clocking of
the digital filters, auto level control, and delta-sigma modulators, and classified into common-audio and
application-specific clocks. Table 2 shows frequencies of the common audio clock and the application-specific
clock. Figure 13 shows timing requirements for system clock inputs. The sampling rate and frequency of the
system clock are determined by settings in 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 8 .
Table 2. Frequency of Common Audio Clock
FREQUENCY
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 UNIT
System clock pulse duration, high t
w(SCKH)
14 ns
System clock pulse duration, low t
w(SCKL)
14 ns
Figure 13. System Clock Timing
The power-on-reset circuit outputs reset signal, typically at V
DD
= 1.2 V, and this circuit does not depend on the
voltage of other power-supplies (V
CC
, V
PA
, and V
IO
). Internal circuits are cleared to default status, then signals
are removed from all analog and digital outputs. The PCM1870 does not require any power supply sequencing.
Register data must be written after turning all power supplies on.
System reset is enabled by setting register 85 (SRST), and all registers are cleared automatically. All circuits are
reset to their default status at once. Note that the PCM1870 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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