LAN8810 Datasheet, PDF (75/83 Pages) Microchip Technology – GMII 10/100/1000 Ethernet Transceiver

LAN8810/LAN8810I
5.6 Clock Circuit
The device can accept either a 25MHz crystal (preferred) or a 25 MHz 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 0V-VDDVARIO 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 5-20 for the recommended crystal specifications.
TABLE 5-20: 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
XI Pin Capacitance
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
-
18
300
-
-
-
-
50
Note 5-24
-
Note 5-25
-
3 typ
-
-
3 typ
-
Units
MHz
PPM
PPM
PPM
PPM
pF
pF
uW
Ohm
o_C
pF
pF
Notes
Note 5-21
Note 5-21
Note 5-22
Note 5-23
Note 5-26
Note 5-26
Note 5-7
Note 5-8
Note 5-9
Note 5-10
Note 5-11
Note 5-12
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).
Frequency Deviation Over Time is also referred to as Aging.
The total deviation for the Transmitter Clock Frequency is specified by IEEE 802.3u as
+/- 50 PPM.
0^oC for commercial version, -40^oC for industrial version.
+70^oC for commercial version, +85^oC for industrial version.
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.
DS00001870B-page 75
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