LAN9500 Datasheet, PDF (204/213 Pages) SMSC Corporation – USB 2.0 to 10/100 Ethernet Controller Promiscuous mode

LAN950x
8.6 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). For the LAN9500A/LAN9500Ai, either a 300uW or 100uW 25MHz crystal may be utilized. For the
LAN9500/LAN9500i, only a 300uW 25MHz crystal may be utilized. The 300uW 25MHz crystal specifications are
detailed in Section 8.6.1, "300uW 25MHz Crystal Specifications," on page 204. The 100uW 25MHz crystal specifications
are detailed in Section 8.6.2, "100uW 25MHz Crystal Specifications (LAN9500A/LAN9500Ai Only)," on page 205.
8.6.1 300UW 25MHZ CRYSTAL SPECIFICATIONS
When utilizing a 300uW 25MHz crystal, the following circuit design (Figure 8-10) and specifications (Table 8-23) are
required to ensure proper operation.
FIGURE 8-10:
300UW 25MHZ CRYSTAL CIRCUIT
LAN950x
56-PIN QFN
XO
XI
Y1
C₁
C₂
TABLE 8-23: 300UW CRYSTAL SPECIFICATIONS
Parameter
Symbol
MIN
NOM
MAX
Units
Notes
Crystal Cut
AT, typ
Crystal Oscillation Mode
Fundamental Mode
Crystal Calibration Mode
Parallel Resonant Mode
Frequency
Frequency Tolerance @ 25^oC
Frequency Stability Over Temp
Frequency Deviation Over Time
Total Allowable PPM Budget
F_fund
F_tol
F_temp
F_age
-
25.000
-
MHz
-
-
+/-50
PPM Note 8-18
-
-
+/-50
PPM Note 8-18
-
+/-3 to 5
-
PPM Note 8-19
-
-
+/-50
PPM Note 8-20
Shunt Capacitance
Load Capacitance
Drive Level
Equivalent Series Resistance
Operating Temperature Range
C_O
-
7 typ
-
pF
C_L
-
20 typ
-
pF
P_W
300
-
-
uW
R₁
-
-
50
Ohm
Note 8-21
-
Note 8-22
o_C
XI Pin Capacitance
-
3 typ
-
pF
Note 8-23
XO Pin Capacitance
-
3 typ
-
pF
Note 8-23
Note 8-18 The maximum allowable values for Frequency Tolerance and Frequency Stability are application
dependent. 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).
DS00001875A-page 204
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