DP83849IFVSSLASHNOPB datasheet(61/108 Pages) TI2

номер детали	DP83849IFVS/NOPB

подробное описание детали	DP83849IF PHYTER™ DUAL Industrial Temperature with Fiber Support (FX) and Flexible Port Switching Dual Port 10/100 Mb/s Ethernet Physical Layer Tranceiver

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CL2

CL1

DP83849IF

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SNOSAX8D – JUNE 2009 – REVISED APRIL 2013

8.4

CLOCK IN (X1) REQUIREMENTS

The DP83849IF supports an external CMOS level oscillator source or a crystal resonator device.

Oscillator

If an external clock source is used, X1 should be tied to the clock source and X2 should be left floating.

Specifications for CMOS oscillators: 25 MHz in MII Mode and 50 MHz in RMII Mode are listed in Table 8-1

and Table 8-2.

Crystal

A 25 MHz, parallel, 20 pF load crystal resonator should be used if a crystal source is desired. Figure 8-3

shows a typical connection for a crystal resonator circuit. The load capacitor values will vary with the

crystal vendors; check with the vendor for the recommended loads.

The oscillator circuit is designed to drive a parallel resonance AT cut crystal with a minimum drive level of

100mW and a maximum of 500 µW. If a crystal is specified for a lower drive level, a current limiting

resistor should be placed in series between X2 and the crystal.

As a starting point for evaluating an oscillator circuit, if the requirements for the crystal are not known, CL1

and CL2 should be set at 33 pF, and R1 should be set at 0Ω.

Specification for 25 MHz crystal are listed in Table 8-3.

Figure 8-3. Crystal Oscillator Circuit

Design Guidelines

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