KS8721CL Micrel, Inc.
M9999-041405 32 April 2005
Single Port Number
Magnetic Manufacturer Part Number Auto-MDI-X of Ports
Pulse H1102 Yes 1
Bel Fuse S558-5999-U7 Yes 1
YCL PH163112 Yes 1
Transpower HB726 Yes 1
Delta LF8505 Yes 1
LanKom LF-H41S Yes 1
Intergrated Transformers
Pulse J0011D21 Yes 1
Pulse J00-0061 Yes 1
Table 8. Qualified Transformer List
Selection of Isolation Transformer
(1)
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.
Characteristic Value Test Condition
Turns Ratio 1 CT : 1 CT
Open-Circuit Inductance (min.) 350µH 100mV, 100kHz, 8mA
Leakage Inductance (max.) 0.4µH 1MHz (min.)
Inter-Winding Capacitance (max.) 12pF
D.C. Resistance (max.) 0.9Ω
Insertion Loss (max.) 1.0dB 0MHz to 65MHz
HIPOT (min.) 1500Vrms
Note:
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 1.3dB can
be compensated or by increasing the line drive current by means of reducing the ISET resistor value. Please select the transformer that supports
auto-MDI/MDI-X.
Selection of Reference Crystal
An oscillator or crystal with the following typical characteristics is recommended.
Characteristic Value Units
Frequency 25.00000 MHz
Frequency Tolerance (max.) ±100 ppm
Load Capacitance (max.) 20 pF
Series Resistance (max.) 40 Ω
