LAN7430 datasheet(68/77 Pages) MICROCHIP

68 / 77 page

LAN7430/LAN7431

DS00002631D-page 68

 2018-2019 Microchip Technology Inc.

7.7

Clock Circuit

The device can accept either a 25MHz crystal (preferred) or a 25 MHz single-ended clock oscillator (+/- 50ppm) input.

If the single-ended clock oscillator method is implemented, XO should be left unconnected and XI should be driven with

a nominal 0-3.3V clock signal. The input clock duty cycle is 40% minimum, 50% typical and 60% maximum.

It is recommended that a crystal utilizing matching parallel load capacitors be used for the crystal input/output signals

(XI/XO). See Table 7-23 for the recommended crystal specifications.

Note 7-44

The maximum allowable values for Frequency Tolerance and Frequency Stability are application

dependent. Since any particular application must meet the IEEE +/-50 PPM Total PPM Budget, the

combination of these two values must be approximately +/-45 PPM (allowing for aging).

Note 7-45

Frequency Deviation Over Time is also referred to as Aging.

Note 7-46

The total deviation for the Transmitter Clock Frequency is specified by IEEE 802.3u as +/- 50 PPM.

Note 7-47

0oC for commercial version, -40oC for industrial and automotive versions.

Note 7-48

+70oC for commercial version, +85oC for industrial version, +105°C for automotive version.

Note 7-49

This number includes the pad, the bond wire and the lead frame. PCB capacitance is not included

in this value. The XO/XI pin and PCB capacitance values are required to accurately calculate the

value of the two external load capacitors. These two external load capacitors determine the accuracy

of the 25.000 MHz frequency.

TABLE 7-23:

CRYSTAL SPECIFICATIONS

Parameter

Symbol

Min

Nom

Max

Units

Notes

Crystal Cut

AT, typ

Crystal Oscillation Mode

Fundamental Mode

Crystal Calibration Mode

Parallel Resonant Mode

Frequency

Ffund

25.000

MHz

Frequency Tolerance @ 25oCFtol

+/-50

PPM

Note 7-44

Frequency Stability Over Temp

Ftemp

+/-50

PPM

Note 7-44

Frequency Deviation Over Time

Fage

+/-3 to 5

PPM

Note 7-45

Total Allowable PPM Budget

+/-50

PPM

Note 7-46

Shunt Capacitance

Load Capacitance

Motional Inductance

Drive Level

100

Equivalent Series Resistance

Ohm

Operating Temperature Range

Note 7-47

Note 7-48

XI Pin Capacitance

2 typ

Note 7-49

XO Pin Capacitance

2 typ

Note 7-49

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