LAN9312 datasheet(454/458 Pages) SMSC

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High Performance Two Port 10/100 Managed Ethernet Switch with 32-Bit Non-PCI CPU Interface

Datasheet

Revision 1.2 (04-08-08)

454

SMSC LAN9312

DATASHEET

15.6

Clock Circuit

The LAN9312 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 15.15 for crystal specifications.

Note 15.11

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 15.12

Frequency Deviation Over Time is also referred to as Aging.

Note 15.13

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

+/- 50 PPM.

Note 15.14

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 15.15 LAN9312Crystal 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 15.11

Frequency Stability Over Temp

Ftemp

+/-50

PPM

Note 15.11

Frequency Deviation Over Time

Fage

+/-3 to 5

PPM

Note 15.12

Total Allowable PPM Budget

+/-50

PPM

Note 15.13

Shunt Capacitance

-7 typ-

Load Capacitance

20 typ

Drive Level

0.5

Equivalent Series Resistance

Ohm

Operating Temperature Range

+70

n/a XI Pin Capacitance

3 typ

Note 15.14

n/a XO Pin Capacitance

3 typ

Note 15.14

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