CS4525 datasheet(27/98 Pages) CIRRUS

27 / 98 page

DS726PP1

CS4525

6.1.1.2

Crystal Oscillator Mode

To use an external crystal in conjunction with the internal crystal driver, a 20 pF fundamental mode par-

allel resonant crystal must be connected between the XTI and XTO pins. This crystal must oscillate within

the frequency ranges specified in the XTI switching specifications table on page 23. Nothing other than

the crystal and its load capacitors should be connected to XTI and XTO. The SYS_CLK pin should be

connected to ground through a 22 k

Ω pull-down resistor to prevent the CS4525 from recognizing system

noise on the SYS_CLK pin as a valid clocking signal.

In this mode, the CS4525 will automatically drive the generated internal clock out of the SYS_CLK pin.

This can be disabled with the EnSysClk bit which will cause the SYS_CLK pin to become high-impedance.

Also, the DivSysClk bit allows the frequency of the generated internal clock to be divided by 2 prior to be-

ing driven out of the SYS_CLK.

It should be noted that the internal oscillator driver is disabled when the CS4525 is in reset (RST is low).

Any external devices connected to the SYS_CLK output will not receive a clock signal until the CS4525

is taken out of reset.

If an external crystal is connected to the XTI/XTO pins while an input clock signal is present on the

SYS_CLK pin following the release of RST, then the CS4525 will automatically use the SYS_CLK pin for

its internal clock. Refer to Section 6.1.1.1 for a details about this mode of operation.

Figure 13 below demonstrates a typical clocking configuration using the crystal oscillator.

Referenced Control

EnSysClk............................. “SYS_CLK Output Enable (EnSysClk)” on page 69

DivSysClk............................ “SYS_CLK Output Divider (DivSysClk)” on page 69

DSP

RST

Reset

SYS_CLK

Clock_In

XTI

XTO

Figure 13. Typical Crystal Oscillator Clocking Configuration

CS4525

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