Datasheet

KSZ9031RNX
DS00002117F-page 67  2016-2017 Microchip Technology Inc.
12.0 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. An optional auto-transformer stage following the chokes provides additional common-
mode noise and signal attenuation.
The KSZ9031RNX 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 four differential
pairs. Therefore, the four transformer center tap pins on the KSZ9031RNX side should not be connected to any power
supply source on the board; rather, 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 voltage could
be different between the four differential pairs, depending on the connected speed mode.
Figure 12-1 shows the typical gigabit magnetic interface circuit for the KSZ9031RNX.
FIGURE 12-1: TYPICAL GIGABIT MAGNETIC INTERFACE CIRCUIT
Table 12-1 lists recommended magnetic characteristics.
Table 12-2 is a list of compatible single-port magnetics with separated transformer center tap pins on the G-PHY chip
side that can be used with the KSZ9031RNX.
TABLE 12-1: MAGNETICS SELECTION CRITERIA
Parameter Value Test Conditions
Turns Ratio 1 CT : 1 CT —
Open-Circuit Inductance (min.) 350 µH 100 mV, 100 kHz, 8 mA
Insertion Loss (max.) 1.0 dB 0 MHz to 100 MHz
HIPOT (min.) 1500 V
RMS
—
TABLE 12-2: COMPATIBLE SINGLE-PORT 10/100/1000 MAGNETICS
Manufacturer Part Number Auto-Transformer Temperature Range Magnetic + RJ-45
Bel Fuse 0826-1G1T-23-F Yes 0°C to 70°C Yes
HALO TG1G-E001NZRL No –40°C to 85°C No
1
2
3
7
8
4
5
6
4x75 Ω
1000 pF / 2kV
R
J
-
45
CONNECTOR
CHASSIS GROUND
(4 x 0.1µF)
TXRXP_A
TXRXM_A
KSZ9031RNX
SIGNAL GROUND
TXRXP_B
TXRXM_B
TXRXP_C
TXRXM_C
TXRXP_D
TXRXM_D