DS_8430_001
78Q8430 Data Sheet
8 Isolation Transformers
Table 35: Isolation Transformers
Name
Value
Condition
Turns Ratio
1 CT : 1 CT ± 5%
350 µH (min)
0.40 µH (max)
12 pF (max)
0.9 Ω (max)
0.4 dB (typ)
1500 Vrms
Open-Circuit Inductance
Leakage Inductance
Inter-Winding Capacitance
D.C. Resistance
Insertion Loss
@ 10 mV, 10 kHz
@ 1 MHz (min)
0 - 65 MHz
HIPOT
Two simple 1:1 isolation transformers are all that are required at the line interface, but transformers
with integrated common-mode choke are recommended for exceeding FCC requirements. Table 35
gives the recommended line transformer characteristics. The 100Base-TX amplitude specifications
assume a transformer loss of 0.4 dB. For the transmit line transformer with higher insertion losses, up to
1.2 dB of insertion loss can be compensated by selecting the appropriate setting in the Transmit
Amplitude Selection bits in register MR19[11:10].
9 Reference Crystal
If the internal crystal oscillator is to be used, a crystal with the characteristics given in Table 36 should be
chosen.
Table 36: Reference Crystal
Name
Value
Units
MHz
pF
Frequency
25.00000
Load Capacitance*
Frequency Tolerance
Oscillation Mode
Parameters at 25 oC ± 2 oC ; Drive Level = 0.5 mW
4**
PPM
≤ ±50 per IEEE 802.3 requirement
Parallel Resonance, Fundamental Mode
Shunt Capacitance (max)
Motional Capacitance (min)
Series Resistance (max)
Spurious Response (max)
10
pF
pF
Ω
10
60
> 5 dB below main within 500 kHz
* Equivalent differential capacitance across the XTLP/XTLN pins.
** If a crystal with a larger load is used, external shunt capacitors to ground should be added to
make up the equivalent capacitance difference.
*** System vendors need to select the proper crystal according to their applications, such as
operating environment, product lifetime, and etc since crystal aging, operating temperature, and
other factors can affect the crystal frequency tolerance.
Rev. 1.2
83
TERIDIAN [ TERIDIAN SEMICONDUCTOR CORPORATION ]
