ICS1893 Datasheet, PDF (32/152 Pages) Integrated Circuit Systems – 3.3-V 10Base-T/100Base-TX Integrated PHYceiver™

ICS1893 Data Sheet - Release
Chapter 6 Interface Overviews
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 61.9Ω 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:
1. 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.
2. Keep all TX traces as short as possible.
3. When making board traces, 50Ω -characteristic impedance is desirable
4. Include a 0Ω resistor in series with TP_CT. (Some systems work better without the TP_CT
connection.)
Figure 6-1. ICS1893 Transmit Twisted Pair
System Ground Plane Chassis Ground Plane
TP_TXP 5
ICS1893
61.9Ω 1%
120 nH
1:1
Center
Tap
Separate Ground Plane
To RJ-45
61.9Ω 1%
TP_TXN 6
0Ω
TP_CT 3
Ideally, for these traces Z_o = 50Ω .
100 pF
75Ω
0.1 µF
ICS1893 Rev C 6/6/00
Copyright © 2000, Integrated Circuit Systems, Inc.
All rights reserved.
32
June, 2000