LAN8700 Datasheet, PDF (57/74 Pages) SMSC Corporation – ±15kV ESD Protected MII/RMII Fast-Ethernet PHY with HP Auto-MDIX and SMSC flexPWR TM in a Small Footprint

LAN8700/LAN8700i
6.6 Clock Circuit
LAN8700/LAN8700i can accept either a 25MHz crystal or a 25MHz single-ended clock oscillator (±50ppm) input for
operation in MII mode. If the single-ended clock oscillator method is implemented, XTAL2 should be left unconnected
and XTAL1/CLKIN should be driven with a nominal 0-3.3V clock signal. The user is required to supply a 50MHz single-
ended clock for RMII operation. The input clock duty cycle is 40% minimum, 50% typical and 60% maximum. See
Table 6-12 for the recommended crystal specifications.
TABLE 6-12: LAN8700/LAN8700I 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
LAN8700/LAN8700i
XTAL1/CLKIN Pin Capacitance
LAN8700/LAN8700i XTAL2 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
-
-
0.5
-
Note 6-4
-
7 typ
20 typ
-
-
-
3 typ
-
-
-
30
Note 6-5
-
-
3 typ
-
Units
MHz
PPM
PPM
PPM
PPM
pF
pF
mW
Ohm
o_C
pF
pF
Notes
Note 6-1
Note 6-1
Note 6-2
Note 6-3
Note 6-6
Note 6-6
Note 6-6
Note 6-1
Note 6-2
Note 6-3
Note 6-4
Note 6-5
Note 6-6
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
±100 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 XTAL1/CLKIN pin, XTAL2 pin and PCB capacitance values are required to
accurately calculate the value of the two external load capacitors. The total load capacitance must
be equivalent to what the crystal expects to see in the circuit so that the crystal oscillator will operate
at 25.000 MHz.
 2007-2016 Microchip Technology Inc.
DS00002260A-page 57