Hi-Speed USB 2.0 to 10/100/1000 Ethernet Controller
Datasheet
7.6
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 7.20 for the recommended crystal specifications.
Table 7.20 LAN7500/LAN7500i Crystal Specifications
PARAMETER
SYMBOL
MIN
NOM
AT, typ
Fundamental Mode
Parallel Resonant Mode
MAX
UNITS
NOTES
Crystal Cut
Crystal Oscillation Mode
Crystal Calibration Mode
Frequency
Ffund
Ftol
-
25.000
-
MHz
PPM
PPM
PPM
PPM
pF
Frequency Tolerance @ 25oC
Frequency Stability Over Temp
Frequency Deviation Over Time
Total Allowable PPM Budget
Shunt Capacitance
-
-
+/-50
Note 7.15
Note 7.15
Note 7.16
Note 7.17
Ftemp
Fage
-
-
+/-50
-
+/-3 to 5
-
-
-
+/-50
CO
CL
-
7 typ
-
Load Capacitance
-
20 typ
-
pF
Drive Level
PW
R1
300
-
-
uW
Equivalent Series Resistance
Operating Temperature Range
-
-
-
50
Ohm
oC
Note 7.18
-
Note 7.19
-
LAN7500/LAN7500i XI Pin
Capacitance
3 typ
pF
Note 7.20
Note 7.20
LAN7500/LAN7500i XO Pin
Capacitance
-
3 typ
-
pF
Note 7.15 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 7.16 Frequency Deviation Over Time is also referred to as Aging.
Note 7.17 The total deviation for the Transmitter Clock Frequency is specified by IEEE 802.3u as
+/- 50 PPM.
Note 7.18 0oC for commercial version, -40oC for industrial version.
Note 7.19 +70oC for commercial version, +85oC for industrial version.
Note 7.20 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.
SMSC LAN7500/LAN7500i
Revision 1.0 (11-01-10)
DATA5S3HEET
SMSC [ SMSC CORPORATION ]
