LXT971ABC datasheet(48/90 Pages) INTEL

48 / 90 page

LXT971A 3.3V Dual-Speed Fast Ethernet Transceiver

Datasheet

Document #: 249414

Revision #: 002

Rev. Date: August 7, 2002

4.0

Application Information

4.1

Magnetics Information

The LXT971A requires a 1:1 ratio for both the receive and transmit transformers. The transformer

isolation voltage should be rated at 2 kV to protect the circuitry from static voltages across the

connectors and cables. Refer to Table 15 for transformer requirements.

A cross-reference list of magnetic manufacturers and part numbers is available in Magnetic

Manufacturers for Networking Product Applications (document number 248991) and is found on

the Intel web site (www.Intel.com). Before committing to a specific component, contact the

manufacturer for current product specifications and validate the magnetics for the specific

application.

4.2

Typical Twisted-Pair Interface

Table 16 provides a comparison of the RJ-45 connections for NIC and Switch applications in a

typical twisted-pair interface setting.

Figure 22 on page 49 shows a typical twisted-pair interface with the RJ-45 connections crossed

over for a Switch configuration. Figure 23 on page 50 provides a typical twisted-pair interface with

the RJ-45 connections configured for a NIC application.

Table 15. Magnetics Requirements

Parameter

Min

Nom

Max

Units

Test Condition

Rx turns ratio

–

1 : 1

–

Tx turns ratio

–

1 : 1

–

Insertion loss

0.0

0.6

1.1

–

Primary inductance

350

–

µH–

Transformer isolation

–

1.5

–

Differential to common mode rejection

–

.1 to 60 MHz

–

60 to 100 MHz

Return Loss

-16

–

30 MHz

-10

–

80 MHz

Table 16. I/O Pin Comparison of NIC and Switch RJ-45 Setups

Symbol

RJ-45

Switch

NIC

TPIP

TPIN

TPOP

TPON

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