KSZ8091MLX Datasheet, PDF (69/72 Pages) Micrel Semiconductor – 10Base-T/100Base-TX Physical Layer Transceiver

Micrel, Inc.
KSZ8091MLX
Magnetic – Connection and Selection
A 1:1 isolation transformer is required at the line interface. Use one with integrated common-mode chokes for designs
exceeding FCC requirements.
The KSZ8091MLX design incorporates voltage-mode transmit drivers and on-chip terminations.
With the voltage-mode implementation, the transmit drivers supply the common-mode voltages to the two differential
pairs. Therefore, the two transformer center tap pins on the KSZ8091MLX side should not be connected to any power
supply source on the board; instead, the center tap pins should be separated from one another and connected through
separate 0.1µF common-mode capacitors to ground. Separation is required because the common-mode voltage is
different between transmitting and receiving differential pairs.
Figure 24 shows the typical magnetic interface circuit for the KSZ8091MLX.
Figure 24. Typical Magnetic Interface Circuit
August 31, 2015
69
Revision 1.2