Datasheet

 2007-2016 Microchip Technology Inc. DS00002260A-page 57
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.
Note 6-1 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 6-2 Frequency Deviation Over Time is also referred to as Aging.
Note 6-3 The total deviation for the Transmitter Clock Frequency is specified by IEEE 802.3u as
±100 PPM.
Note 6-4 0
o
C for commercial version, -40
o
C for industrial version.
Note 6-5 +70
o
C for commercial version, +85
o
C for industrial version.
Note 6-6 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.
TABLE 6-12: LAN8700/LAN8700I 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 6-1
Frequency Stability Over Temp F
temp
- - ±50 PPM Note 6-1
Frequency Deviation Over Time F
age
- +/-3 to 5 - PPM Note 6-2
Total Allowable PPM Budget - - ±50 PPM Note 6-3
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 Note 6-4 - Note 6-5
o
C Note 6-6
LAN8700/LAN8700i
XTAL1/CLKIN Pin Capacitance
-3 typ-pFNote 6-6
LAN8700/LAN8700i XTAL2 Pin
Capacitance
-3 typ-pFNote 6-6