Datasheet

 2018 Microchip Technology Inc. DS00002813A-page 35
KSZ8721BL/SL
7.7 Selection of Isolation Transformers
One simple 1:1 isolation transformer is needed at the line interface. An isolation transformer with integrated common-
mode choke is recommended for exceeding FCC requirements. The following table gives recommended transformer
characteristics.
Note 7-1 The IEEE 802.3u standard for 100BASE-TX assumes a transformer loss of 0.5dB. For the transmit
line transformer, insertion loss of up to 1.3 dB can be compensated or by increasing the line drive
current by means of reducing the I
SET
resistor value. Please select the transformer that supports
auto-MDI/MDI-X.
7.8 Selection of Reference Crystal
An oscillator or crystal with the following typical characteristics is recommended.
TABLE 7-7: SELECTION OF ISOLATION TRANSFORMERS (Note 7-1)
Parameter Value Test Condition
Turns ratio 1 CT : 1 CT —
Open-circuit inductance (min) 350 µH 100 mV, 100 kHz, 8 mA
Leakage inductance (max) 0.4 µH 1 MHz (min)
Inter-winding capacitance (max) 12 pF —
D.C. resistance (max) 0.9Ω —
Insertion loss (max) 1.0 dB 0 MHz - 65 MHz
HIPOT (min) 1500V
rms
—
TABLE 7-8: SELECTION OF ISOLATION TRANSFORMERS
Characteristics Value
Frequency 25 MHz
Frequency tolerance (max) ±100 ppm
Load capacitance (max) 20 pF
Series resistance (max) 40Ω
TABLE 7-9: QUALIFIED SINGLE PORT TRANSFORMER LISTS
Single Port Magnetic Manufacturer Part Number Auto MDIX
Pulse H1102 Yes
Bel Fuse S558-5999-U7 Yes
YCL PT163020 Yes
Transpower HB726 Yes
Delta LF8505 Yes
LanKom LF-H41S Yes
Integrated Transformers
Pulse J0011D21 Yes
Pulse J00-0061 Yes