ICS1893 datasheet(32/152 Pages) ICST

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ICS1893 Rev C 6/6/00

June, 2000

Chapter 6

Interface Overviews

ICS1893 Data Sheet - Release

6.5.1

Twisted-Pair Transmitter Interface

The twisted-pair transmitter driver uses an H-bridge configuration, which requires that the transmit

transformer not have a choke on the chip side. ICS suggests any of the following for the H-bridge:

• Halo TG22S012ND transformer

• Transpower HB617-LP transformer

• Pulse 68517 transformer, which can be turned around to move the choke windings to the RJ-45 side

Figure 6-1 shows the design for the ICS1893 twisted-pair transmitter interface.

• Two 61.9

Ω 1% resistors are in series, with a 120-nH 5% inductor between them. These components

form a network that connects across both the transformer and the ICS1893 TP_TXP and TP_TXN pins.

• The ICS1893 supplies the power to the transformer. (No VDD connection is required.)

• The ICS1893 TP_CT pin is connected directly to the transformer transmit center tap connection and is

bypassed to ground with a 100-pF capacitor. The transformer center tap must not connect to the

resistor/inductor network.

Note:

If the transmit transformer has a choke, put a choke on the RJ-45 side. Do not put a choke on the

ICS1893 side of the transformer for the transmit windings.

Keep all TX traces as short as possible.

When making board traces, 50

Ω-characteristic impedance is desirable

Include a 0

Ω resistor in series with TP_CT. (Some systems work better without the TP_CT

connection.)

Figure 6-1.

ICS1893 Transmit Twisted Pair

ICS1893

TP_TXP 5

TP_TXN 6

TP_CT 3

61.9

Ω 1%

120 nH

61.9

Ω 1%

To RJ-45

1:1

System Ground Plane

Chassis Ground Plane

Ω

0.1

µF

Separate Ground Plane

Ideally, for these traces Zo = 50Ω .

Center

Tap

100 pF

Ω

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