Datasheet

 2013-2015 Microchip Technology Inc. DS00001987A-page 125
LAN8740A/LAN8740Ai
3: The total deviation for the Transmitter Clock Frequency is specified by IEEE 802.3u as
±50 ppm.
4: 0°C for commercial version, -40°C for industrial version
5: +70°C for commercial version, +85°C for industrial version
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. These two external load capacitors determine the accuracy of
the 25.000 MHz frequency.
5.7.2 100 µW 25 MHZ CRYSTAL SPECIFICATIONS
When utilizing a 100 µW 25 MHz crystal, the following circuit design (Figure 5-9) and specifications (Table 5-16) are
required to ensure proper operation.
FIGURE 5-9: 100 µW 25 MHZ CRYSTAL CIRCUIT
TABLE 5-16: 100 µW CRYSTAL SPECIFICATIONS
Parameter Symbol Min. Nom. Max. Unit Note
Crystal Cut AT, typ
Crystal Oscillation Mode Fundamental Mode
Crystal Calibration Mode Parallel Resonant Mode
Frequency F
fund
- 25.000 - MHz
Frequency Tolerance at 25
o
CF
tol
- - ±50 ppm (see Note 1)
Frequency Stability Over Temp F
temp
- - ±50 ppm (see Note 1)
Frequency Deviation Over Time F
age
- ±3 to 5 - ppm (see Note 2)
Total Allowable PPM Budget - - ±50 ppm (see Note 3)
Shunt Capacitance C
O
--5pF
Load Capacitance C
L
8- 12pF
Drive Level P
W
- 100 - µW (see Note 4)
Equivalent Series Resistance R
1
--80Ω
XTAL2 Series Resistor R
S
495 500 505 Ohm
Operating Temperature Range (see Note 5)- (see Note 6)
o
C
XTAL1/CLKIN Pin Capacitance - 3 typ - pF (see Note 7)
XTAL2 Pin Capacitance - 3 typ - pF (see Note 7)
LAN8740
XTAL2
XTAL1
R
S
Y1
C
1
C
2