LAN9420 Datasheet, PDF (167/171 Pages) SMSC Corporation – Single-Chip Ethernet Controller with HP Auto-MDIX Support and PCI Interface

Single-Chip Ethernet Controller with HP Auto-MDIX Support and PCI Interface
Datasheet
5.9
Clock Circuit
LAN9420/LAN9420i 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 5.13 for the recommended crystal specifications.
Table 5.13 LAN9420/LAN9420i Crystal Specifications
PARAMETER
Crystal Cut
Crystal Oscillation Mode
Crystal Calibration Mode
Frequency
Frequency Tolerance @ 25^oC
Frequency Stability Over Temp
Frequency Deviation Over Time
Total Allowable PPM Budget
Shunt Capacitance
Load Capacitance
Drive Level
Equivalent Series Resistance
Operating Temperature Range
LAN9420/LAN9420i XI Pin
Capacitance
LAN9420/LAN9420i XO Pin
Capacitance
SYMBOL
F_fund
F_tol
F_temp
F_age
C_O
C_L
P_W
R₁
MIN
NOM
MAX
AT, typ
Fundamental Mode
Parallel Resonant Mode
-
25.000
-
-
-
+/-50
-
-
+/-50
-
+/-3 to 5
-
-
-
+/-50
-
7 typ
-
-
20 typ
-
0.5
-
-
-
-
50
Note 5.20
-
Note 5.21
-
3 typ
-
UNITS
MHz
PPM
PPM
PPM
PPM
pF
pF
mW
Ohm
o_C
pF
NOTES
Note 5.17
Note 5.17
Note 5.18
Note 5.19
Note 5.22
-
3 typ
-
pF
Note 5.22
Note 5.17
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 5.18 Frequency Deviation Over Time is also referred to as Aging.
Note 5.19 The total deviation for the Transmitter Clock Frequency is specified by IEEE 802.3u as
+/- 50 PPM.
Note 5.20 0^oC for commercial version, -40^oC for industrial version.
Note 5.21 +70^oC for commercial version, +85^oC for industrial version.
Note 5.22
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 LAN9420/LAN9420i
167
DATASHEET
Revision 1.6 (07-18-11)