LAN9312 Datasheet, PDF (454/458 Pages) SMSC Corporation – High Performance Two Port 10/100 Managed Ethernet Switch with 32-Bit Non-PCI CPU Interface

15.6
High Performance Two Port 10/100 Managed Ethernet Switch with 32-Bit Non-PCI CPU Interface
Datasheet
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.
Table 15.15 LAN9312Crystal 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
n/a XI Pin Capacitance
n/a 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
-
-
-
-
30
0
-
+70
-
3 typ
-
-
3 typ
-
UNITS NOTES
MHz
PPM
PPM
PPM
PPM
pF
pF
mW
Ohm
o_C
pF
pF
Note 15.11
Note 15.11
Note 15.12
Note 15.13
Note 15.14
Note 15.14
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.
Revision 1.2 (04-08-08)
454
DATASHEET
SMSC LAN9312