LAN8740A Datasheet, PDF (124/136 Pages) Microchip Technology – Small Footprint MII/RMII 10/100 Energy Efficient Ethernet Transceiver with HP Auto-MDIX and flexPWR® Technology

LAN8740A/LAN8740Ai
5.7 Clock Circuit
The device can accept either a 25 MHz crystal or a 25 MHz single-ended clock oscillator (±50ppm) input. If the single-
ended clock oscillator method is implemented, XTAL2 should be left unconnected and XTAL1/CLKIN should be driven
with a nominal 0-3.3 V 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
(XTAL1/XTAL2). Either a 300 µW or 100 µW 25 MHz crystal may be utilized. The 300 µW 25 MHz crystal specifications
are detailed in Section 5.7.1, "300 µW 25 MHz Crystal Specifications". The 100 µW 25 MHz crystal specifications are
detailed in Section 5.7.2, "100 µW 25 MHz Crystal Specifications".
5.7.1 300 µW 25 MHZ CRYSTAL SPECIFICATIONS
When utilizing a 300 µW 25 MHz crystal, the following circuit design (Figure 5-8) and specifications (Table 5-15) are
required to ensure proper operation.
FIGURE 5-8:
300 µW 25 MHZ CRYSTAL CIRCUIT
LAN8740
XTAL2
XTAL1
Y1
C₁
C₂
TABLE 5-15: 300 µW CRYSTAL SPECIFICATIONS
Parameter
Symbol
Min.
Nom.
Max.
Unit
Note
Crystal Cut
Crystal Oscillation Mode
Crystal Calibration Mode
Frequency
Frequency Tolerance at 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
XTAL1/CLKIN Pin Capacitance
XTAL2 Pin Capacitance
AT, typ
Fundamental Mode
Parallel Resonant Mode
F_fund
-
F_tol
-
F_temp
-
F_age
-
-
C_O
-
C_L
-
P_W
300
R₁
-
(see Note 4)
-
-
25.000
-
-
±3 to 5
-
7 typ
20 typ
-
-
-
3 typ
3 typ
-
MHz
±50
ppm
±50
ppm
-
ppm
±50
ppm
-
pF
-
pF
-
µW
50
Ω
(see Note 5) ^oC
-
pF
-
pF
(see Note 1)
(see Note 1)
(see Note 2)
(see Note 3)
(see Note 6)
(see Note 6)
Note 1: 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).
2: Frequency Deviation Over Time is also referred to as Aging.
DS00001987A-page 124
 2013-2015 Microchip Technology Inc.