DP83848JSQSLASHNOPB datasheet(65/84 Pages) TI1

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1:1

RJ45

NOTE: CENTER TAP IS PULLED TO VDD

*PLACE CAPACITORS CLOSE TO THE

TRANSFORMER CENTER TAPS

RD-

RD+

TD-

TD+

0.1 PF*

COMMON MODE CHOKES

MAY BE REQUIRED

0.1 PF

Vdd

All values are typical and are +/- 1%

49.9 :

PLACE RESISTORS AND

CAPACITORS CLOSE TO

THE DEVICE

TPRDM

TDRDP

TPTDM

TPTDP

DP83848H, DP83848J, DP83848K, DP83848M, DP83848T

www.ti.com

SNLS250E – MAY 2008 – REVISED APRIL 2015

Figure 7-2. 10/100 Mb/s Twisted Pair Interface

7.2.1.2

Clock IN (X1) Recommendations

The DP83848x supports an external CMOS level oscillator source or a crystal resonator device.

7.2.1.2.1 Oscillator

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

The CMOS oscillator specifications for MII Mode are listed in Table 7-1. For RMII Mode, the CMOS

oscillator specifications are listed in Table 7-2. For RMII mode, it is not recommended that the system

clock out, Pin 21 of DP83848H, DP83848M, or DP83848T devices, be used as the reference clock to the

MAC without first verifying the interface timing. See AN-1405 for more details.

7.2.1.2.2 Crystal

A 25-MHz, parallel, 20-pF load crystal resonator should be used if a crystal source is desired. Figure 7-3

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

100 µW 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 0

Ω.

Specification for 25-MHz crystal are listed in Table 7-3.

Application, Implementation, and Layout

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Product Folder Links: DP83848H DP83848J DP83848K DP83848M DP83848T

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