LAN8741AI-EN datasheet(94/106 Pages) MICROCHIP

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LAN8741A/LAN8741Ai

DS00001988A-page 94

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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.

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.

FIGURE 5-8:

300 µW 25 MHZ CRYSTAL CIRCUIT

TABLE 5-15:

300 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

Ffund

25.000

MHz

Frequency Tolerance at 25oCFtol

±50

ppm

(see Note 1)

Frequency Stability Over Temp

Ftemp

±50

ppm

(see Note 1)

Frequency Deviation Over Time

Fage

±3 to 5

ppm

(see Note 2)

Total Allowable PPM Budget

±50

ppm

(see Note 3)

Shunt Capacitance

-7 typ

Load Capacitance

20 typ

Drive Level

300

µW

Equivalent Series Resistance

--50

Ω

Operating Temperature Range

(see Note 4)-

(see Note 5) oC

XTAL1/CLKIN Pin Capacitance

3 typ

(see Note 6)

XTAL2 Pin Capacitance

3 typ

(see Note 6)

LAN8741

XTAL2

XTAL1

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