LAN9500AI datasheet(204/213 Pages) MICROCHIP

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LAN950x

DS00001875A-page 204

 2010 - 2015 Microchip Technology Inc.

8.6

Clock Circuit

The device can accept either a 25MHz crystal (preferred) or a 25MHz 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). For the LAN9500A/LAN9500Ai, either a 300uW or 100uW 25MHz crystal may be utilized. For the

LAN9500/LAN9500i, only a 300uW 25MHz crystal may be utilized. The 300uW 25MHz crystal specifications are

detailed in Section 8.6.1, "300uW 25MHz Crystal Specifications," on page 204. The 100uW 25MHz crystal specifications

are detailed in Section 8.6.2, "100uW 25MHz Crystal Specifications (LAN9500A/LAN9500Ai Only)," on page 205.

8.6.1

300UW 25MHZ CRYSTAL SPECIFICATIONS

When utilizing a 300uW 25MHz crystal, the following circuit design (Figure 8-10) and specifications (Table 8-23) are

required to ensure proper operation.

Note 8-18

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).

FIGURE 8-10:

300UW 25MHZ CRYSTAL CIRCUIT

TABLE 8-23:

300UW 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 8-18

Frequency Stability Over Temp

Ftemp

+/-50

PPM

Note 8-18

Frequency Deviation Over Time

Fage

+/-3 to 5

PPM

Note 8-19

Total Allowable PPM Budget

+/-50

PPM

Note 8-20

Shunt Capacitance

-7 typ-

Load Capacitance

20 typ

Drive Level

300

Equivalent Series Resistance

Ohm

Operating Temperature Range

Note 8-21

Note 8-22

XI Pin Capacitance

3 typ

Note 8-23

XO Pin Capacitance

3 typ

Note 8-23

LAN950x

56-PIN QFN

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