ST72774 datasheet(19/144 Pages) STMICROELECTRONICS

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ST72774/ST727754/ST72734

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CLOCK SYSTEM (Cont’d)

3.1.2 Crystal Resonator

The internal oscillator is designed to operate with

AT-cut

parallel

resonant

quartz

crystal

resonator in the frequency range specified for fosc.

The circuit shown in Figure 8 is recommended

when

using

crystal,

and

Table 4,

“.

Recommended Crystal Values,” on page 19 lists

the recommended capacitance and feedback

resistance values. The crystal and associated

components should be mounted as close as

possible to the input pins in order to minimize

output distortion and start-up stabilization time.

Figure 8. Crystal/Ceramic Resonator

Table 4

. Recommended Crystal Values

Legend:

CL1, CL2 = Maximum total capacitance on pins

OSCIN and OSCOUT (the value includes the

external capacitance tied to the pin plus the

parasitic capacitance of the board and of the

device).

RSMAX = Maximum series parasitic resistance of

the quartz allowed.

Note: The tables are relative to the quartz crystal

only (not ceramic resonator).

3.1.3 External Clock

An external clock should be applied to the OSCIN

input with the OSCOUT pin not connected as

shown in Figure 9. The Crystal clock specifications

do not apply when using an external clock input.

The equivalent specification of the external clock

source should be used.

Figure 9. External Clock Source Connections

OSCIN

OSCOUT

CL1

CL2

CRYSTAL CLOCK

1M*

*Recommended for oscillator stability

24 Mhz

Unit

RSMAX

Ohms

CL1

CL2

OSCIN

OSCOUT

EXTERNAL

CLOCK

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