Datasheet

Micrel, Inc.
KSZ8081MNX/KSZ8081RNB
August
19, 2015 66
Revision 1.4
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 KSZ8081MNX/RNB 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 KSZ8081MNX/RNB 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 26 shows the typical magnetic interface circuit for the KSZ8081MNX/RNB.
Figure 26. Typical Magnetic Interface Circuit