VSC8221 datasheet(116/138 Pages) MICROSEMI

116 / 138 page

VSC8221

Data Sheet

VMDS-10106 Revision 4.1

December 2006

116 of 123

123

26 CLOCKING SPECIFICATIONS

26.1 Reference Clock Option

The following component specifications should be used to select a clock reference for use with the VSC8221. For more

information about clocking and frequency offset tolerance specifications when jumbo packet support is required, see the

application note Using Jumbo Packets with SimpliPHYs, available from the Microsemi Web site.

26.2 Crystal Option

The following component specifications should be used to select a crystal for use with the VSC8221. For more information

about clocking and frequency offset tolerance specifications when jumbo packet support is required, see the application note

Using Jumbo Packets with SimpliPHYs

, available from the Microsemi Web site.

Table 50. Reference Clock Option Specifications

Symbol

Min

Typ

Max

Unit

Parameter Description & Conditions

FTOL-25MHZ

-100 ppm

+100 ppm

MHz

Total frequency offset tolerance (25 MHz clock

option), including, initial offset, stability over

temperature.

TR1, TF1

4ns

Rise and fall time (20% to 80%), 25 MHz clock

option.

TR2, TF2

0.8

Rise and fall time (20% to 80%), 125 MHz clock

option.

DUTY

Duty cycle (25 MHz and 125 MHz clock

options).

Table 51. Crystal Option Specifications

Symbol

Min

Typ

Max

Unit

Parameter Description & Conditions

FREF

MHz

Fundamental mode, AT-cut type, parallel

resonant crystal reference frequency.

FTOL(TOTAL)

-50

+50

ppm

Fundamental mode, AT-cut type, parallel

resonant crystal total frequency offset, including,

initial offset, stability over temperature, aging

and capacitive loading.

Crystal parallel load capacitance.

CL-EXT

Crystal external load capacitors to GND.1

1 These values can depend on board parasitics.

ESR

Ω

Equivalent series resistance of crystal.

0.5

Crystal oscillator drive level.

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