Datasheet
®
12
PCM3501
SYSTEM CLOCK AND RESET/
POWER DOWN
SYSTEM CLOCK INPUT AND OUTPUT
The PCM3501 requires a system clock for operating the
digital filters and delta-sigma data converters.
The system clock may be supplied from an external master
clock or generated using the on-chip crystal oscillator cir-
cuit. Figure 1 shows the required connections for external
and crystal clock operation. The system clock must operate
at 512 times the sampling frequency, f
S
, with sampling
frequencies from 7.2kHz to 26kHz. This gives an effective
system clock frequency range of 3.6864MHz to 13.312MHz.
Table I shows system clock frequencies for common sam-
pling frequencies.
For external clock operation, XTI (pin 17) or SCKIO (pin 15)
is driven by a master clock source. If SCKIO is used as the
system clock input, then XTI must be connected to ground.
SAMPLING FREQUENCY (kHz) SYSTEM CLOCK FREQUENCY (MHz)
8 4.096
11.025 5.6448
16 8.192
22.05 11.2896
24 12.288
TABLE I. System Clock Frequencies for Common Sam-
pling Frequencies.
FIGURE 1. System Clock Generation.
For either case, XTO (pin 16) should be left open. The system
clock source should be free of noise and exhibit low phase
jitter in order to obtain optimal dynamic performance from
the PCM3501. Figure 2 shows the system clock timing
requirements associated with an external master clock.
For crystal oscillator operation, a crystal is connected be-
tween XTI (pin 17) and XTO (pin 16), along with the
necessary load capacitors (10pF to 33pF per pin, as shown
in Figure 1). A fundamental-mode, parallel resonant crystal
is required.
FIGURE 2. External System Clock Timing Requirements.
System Clock Pulse Width HIGH t
CLKIH
20ns (min)
System Clock Pulse Width LOW t
CLKIL
20ns (min)
t
CLKIH
t
CLKIL
1/512f
S
0.7V
DD
"H"
XTI
or
SCKIO
"L"
0.3V
DD
C
1
C
2
C
1
, C
2
= 10pF to 33pF
XTI
R
Crystal
XTO
PCM3501
SCKIO
CRYSTAL RESONATOR
CONNECTION
External
Clock
External
Clock
XTI
XTO
R
PCM3501
EXTERNAL CLOCK INPUT-XTI
(XTO must be open)
SCKIO
XTI
XTO
R
PCM3501
EXTERNAL CLOCK INPUT-SCKIO
(XTO must be open)
SCKIO