LAN9500AI datasheet(63/66 Pages) SMSC

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USB 2.0 to 10/100 Ethernet Controller

Datasheet

SMSC LAN950x Family

Revision 1.1 (04-18-13)

DATASHEET

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). See Table 8.23 for the recommended crystal specifications.

Note 8.18 The maximum allowable values for Frequency Tolerance and Frequency Stability are

application dependant. 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 8.19 Frequency Deviation Over Time is also referred to as Aging.

Note 8.20 The total deviation for the Transmitter Clock Frequency is specified by IEEE 802.3u as

+/- 50 PPM.

Note 8.21 0oC for commercial version, -40oC for industrial version.

Note 8.22 +70oC for commercial version, +85oC for industrial version.

Note 8.23 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 8.23 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 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

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