LAN88730 datasheet(71/82 Pages) MICROCHIP

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DS60001256B-page 71

LAN88730

3: The total deviation for the Transmitter Clock Frequency is specified by IEEE 802.3u as

±50 ppm.

4: +85oC for grade A temperature range, +105oC for grade B temperature range

5: 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.

5.8.2

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.

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 5-9:

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

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

--5

Load Capacitance

Drive Level

100

µW

(see Note 4)

Equivalent Series Resistance

--80

Ω

XTAL2 Series Resistor

495

500

505

Ohm

Operating Temperature Range

-40

(see Note 5) oC

XTAL1/CLKIN Pin Capacitance

3 typ

(see Note 6)

XTAL2 Pin Capacitance

3 typ

(see Note 6)

LAN88730

XTAL2

XTAL1

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