
Micrel, Inc.
KSZ8041NL/RNL
September 2010
53
M9999-090910-1.4
Selection of Isolation Transformer
A 1:1 isolation transformer is required at the line interface. An isolation transformer with integrated common-mode chokes
is recommended for exceeding FCC requirements.
The Table 17 gives recommended transformer characteristics.
Parameter
Value
Test Condition
Turns ratio
1 CT : 1 CT
Open-circuit inductance (min.)
350
μH
100mV, 100kHz, 8mA
Leakage inductance (max.)
0.4
μH
1MHz (min.)
Inter-winding capacitance (typ.)
12pF
D.C. resistance (typ.)
0.9
Ω
Insertion loss (max.)
-1.0dB
0MHz – 65MHz
HIPOT (min.)
1500Vrms
Table 17. Transformer Selection Criteria
Magnetic Manufacturer
Part Number
Auto MDI-X
Number of Port
Bel Fuse
S558-5999-U7
Yes
1
Bel Fuse (Mag Jack)
SI-46001
Yes
1
Bel Fuse (Mag Jack)
SI-50170
Yes
1
Delta
LF8505
Yes
1
LanKom
LF-H41S
Yes
1
Pulse
H1102
Yes
1
Pulse (low cost)
H1260
Yes
1
Transpower
HB726
Yes
1
TDK (Mag Jack)
TLA-6T718
Yes
1
Table 18. Qualified Single Port Magnetics
Selection of Reference Crystal
Characteristics
Value
Units
Frequency
25
MHz
Frequency tolerance (max)
±50
ppm
Load capacitance
20
pF
Series resistance
40
Ω
Table 19. Typical Reference Crystal Characteristics