Datasheet

KSZ8081MNX/RNB
DS00002202C-page 58  2016-2018 Microchip Technology Inc.
7.13 Magnetic – Connection and Selection
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 0.1
µF common-mode capacitors to ground. Separation is required because the common-mode volt-
age is different between transmitting and receiving differential pairs.
Figure 7-16 shows the typical magnetic interface circuit for the KSZ8081MNX/RNB.
FIGURE 7-16: TYPICAL MAGNETIC INTERFACE CIRCUIT
Table 7-13 lists recommended magnetic characteristics.
TABLE 7-13: MAGNETICS SELECTION CRITERIA
Parameter Value Test Condition
Turns ratio 1 CT : 1 CT —
Open-circuit inductance (minimum) 350 µH 100 mV, 100 kHz, 8 mA
Insertion loss (typical) –1.1 dB 100 kHz to 100 MHz
HIPOT (minimum) 1500 V
rms
—
1
2
3
7
8
4
5
6
4 x 75Ω
1000pF/2kV
RJ-45 CONNECTOR
CHASSIS GROUND
(2 x 0.1μF)
TXP
TXM
RXP
RXM
KSZ8081MNX/RNB
SIGNAL GROUND