
Application Information
Copyright 1999-2002 by LSI Logic Corporation. All rights reserved.
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April, 2002
application, it might be necessary to adjust the value of the output current
to compensate for external loading. The TP output level can be adjusted
by changing the value of the external resistor tied to RXT.
4.4 Transmitter Droop
The IEEE 802.3 specification has a transmitter output droop requirement
for 100BaseTX. Since the L84225 TP output is a current source, it has
no perceptible droop by itself. However, the open circuit inductance of the
transformer added to the device transmitter output as shown in
Figure 11
will cause droop to appear at the transmit interface to the TP wire. If the
transformer connected to the L84225 outputs meets the requirements in
Table 21
, the transmit interface to the TP cable will meet the IEEE 802.3
droop requirements.
4.5 Fiber Interface
4.5.1 General
The L84225 uses a PECL-type driver/receiver to achieve a throughput of
100 Mbps across a differential fiber interface. The interface comprises
four signals: FXOP/ FXON (output) and FXIP/FXIN (input).
Some Fiber transceivers modules that will work with the L84225 are
shown in
Table 23
. The Siemens Fiber Transceiver V23809-C8-C10
operates at 3.3V for use with the L84225. 5V Fiber modules such as the
HP HFBR-5103 will also operate with the proper termination network
described later.
The L84225 fiber interface is enabled for each channel independently if
a valid PECL Fiber signal is tied to the SD_[3:0]/FXEN_[3:0] pins; the
Table 23
Fiber Transceiver Modules
Vendor
3.3V
5V
Siemens
1
1. Siemens part operates at both 3.3V and 5V supply values.
V23809-C8-C10
V23809-C8-C10
HP
Available Soon
HFBR-5103
Amp
Contact Supplier
269040-1