Datasheet

High Performance Single-Chip 10/100 Non-PCI Ethernet Controller
Datasheet
Revision 1.5 (07-11-08) 130 SMSC LAN9118
DATASHEET
7.6 Clock Circuit
The LAN9118 can accept either a 25MHz crystal (preferred) or a 25 MHz clock oscillator (±50 PPM)
input. The LAN9118 shares the 25MHz clock oscillator input (CLKIN) with the crystal input XTAL1 (pin
6). If the single-ended clock oscillator method is implemented, XTAL2 should be left unconnected and
CLKIN 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 LAN9118
crystal input/output signals (XTAL1, XTAL2). See Table 7.6, "LAN9118 Crystal Specifications" for crystal
specifications. Refer to SMSC Application Note AN10.7 - “Parallel Crystal Circuit Input Voltage Control”
and the LAN9118 Reference Schematic for additional information.
Note 7.11 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 7.12 Frequency Deviation Over Time is also reffered to as Aging.
Note 7.13 The total deviation for the Transmitter Clock Frequency is specified by IEEE 802.3u as
+/- 50 PPM.
Note 7.14 This number includes the pad, the bond wire and the lead frame. PCB capacitance is not
included in this value. The XTAL1 and XTAL2 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.
Table 7.6 LAN9118 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 F
fund
- 25.000 - MHz
Frequency Tolerance @ 25
o
CF
tol
- - +/-50 PPM Note 7.11
Frequency Stability Over Temp F
temp
- - +/-50 PPM Note 7.11
Frequency Deviation Over Time F
age
- +/-3 to 5 - PPM Note 7.12
Total Allowable PPM Budget - - +/-50 PPM Note 7.13
Shunt Capacitance C
O
-7 typ-pF
Load Capacitance C
L
- 20 typ - pF
Drive Level P
W
0.5 - - mW
Equivalent Series Resistance R
1
--30Ohm
Operating Temperature Range 0 - +70
o
C
LAN9118 XTAL1 Pin
Capacitance
-3 typ-pFNote 7.14
LAN9118 XTAL2 Pin
Capacitance
-3 typ-pFNote 7.14