Справочник Пользователя для SMSC LAN9500i

Hi-Speed USB 2.0 to 10/100 Ethernet Controller

SMSC LAN9500/LAN9500i

39

Revision 1.7 (10-02-08)

 

LAN9500/LAN9500i 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 

 for the recommended crystal specifications.

Note 4.15 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 4.16 Frequency Deviation Over Time is also referred to as Aging.

Note 4.17 The total deviation for the Transmitter Clock Frequency is specified by IEEE 802.3u as 

+/- 50 PPM.

Note 4.18 0

o

C for commercial version, -40

o

C for industrial version.

Note 4.19 +70

o

C for commercial version, +85

o

C for industrial version.

Note 4.20 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.

Crystal Cut

AT, typ

Crystal Oscillation Mode

Fundamental Mode

Crystal Calibration Mode

Parallel Resonant Mode

Frequency

F

fund

-

25.000

-

MHz

Frequency Tolerance @ 25

o

C

F

tol

-

-

+/-50

PPM

Frequency Stability Over Temp

F

temp

-

-

+/-50

PPM

Frequency Deviation Over Time

F

age

-

+/-3 to 5

-

PPM

Total Allowable PPM Budget

-

-

+/-50

PPM

Shunt Capacitance

C

O

-

7  typ

-

pF

Load Capacitance

C

L

-

20 typ

-

pF

Drive Level

P

W

300

-

-

uW

Equivalent Series Resistance

R

1

-

-

50

Ohm

Operating Temperature Range

-

o

C

LAN9500/LAN9500i XI Pin 
Capacitance

-

3  typ

-

pF

LAN9500/LAN9500i XO Pin 
Capacitance

-

3  typ

-

pF