PCM3500ESLASH2K datasheet(12/26 Pages) TI

12 / 26 page

PCM3500

SYSTEM CLOCK AND RESET/

POWER DOWN

SYSTEM CLOCK INPUT AND OUTPUT

The PCM3500 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, fS, 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)

4.096

11.025

5.6448

8.192

22.05

11.2896

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 PCM3500. 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.

1, C2 = 10pF to 33pF

XTI

Crystal

XTO

PCM3500

SCKIO

CRYSTAL RESONATOR

CONNECTION

External

Clock

External

Clock

XTI

XTO

PCM3500

EXTERNAL CLOCK INPUT-XTI

(XTO must be open)

SCKIO

XTI

XTO

PCM3500

EXTERNAL CLOCK INPUT-SCKIO

(XTO must be open)

SCKIO

System Clock Pulse Width HIGH t

CLKIH

20ns (min)

System Clock Pulse Width LOW

CLKIL

20ns (min)

CLKIH

CLKIL

1/512f

0.7V

"H"

XTI

SCKIO

"L"

0.3V

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