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Micrel, Inc.
KSZ9021GQ
September 2010
57
M9999-091010-1.2
Reference Clock – Connection & Selection
A crystal or external clock source, such as an oscillator, is used to provide the reference clock for the KSZ9021GQ. The
reference clock is 25 MHz for all operating modes of the KSZ9021GQ.
The following figure and table shows the reference clock connection to XI (pin 124) and XO (pin 123) of the KSZ9021GQ,
and the reference clock selection criteria.
25MHz OSC
+/-50ppm
NC
XI
XO
XI
XO
22pF
25MHz XTAL
+/-50ppm
Figure 16. 25MHz Crystal / Oscillator Reference Clock Connection
Characteristics
Value
Units
Frequency
25
MHz
Frequency tolerance (max)
±50
ppm
Table 17. Reference Crystal/Clock Selection Criteria
Magnetics Specification
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 following tables provide recommended magnetic characteristics and a list of qualified magnetics for the KSZ9021GQ.
Parameter
Value
Test Condition
Turns ratio
1 CT : 1 CT
Open-circuit inductance (min.)
350
μH
100mV, 100kHz, 8mA
Insertion loss (max.)
1.0dB
0MHz – 100MHz
HIPOT (min.)
1500Vrms
Table 18. Magnetics Selection Criteria
Magnetic Manufacturer
Part Number
Auto MDI-X
Number of Port
Pulse
H5007NL
Yes
1
TDK
TLA-7T101LF
Yes
1
Table 19. Qualified Single Port 10/100/1000 Magnetics