78q8430-100igt Maxim Integrated Products, Inc., 78q8430-100igt Datasheet - Page 83

• Manufacturer Part Number: 78q8430-100igt
• Description: 10/100 Ethernet Mac And Phy
• Manufacturer: Maxim Integrated Products, Inc.

DS_8430_001
8 Isolation Transformers
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.
Rev. 1.2
Name
Turns Ratio
Open-Circuit Inductance
Leakage Inductance
Inter-Winding Capacitance
D.C. Resistance
Insertion Loss
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
* 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
*** 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.
Name
Frequency
Load Capacitance*
Frequency Tolerance
Oscillation Mode
Parameters at 25
Shunt Capacitance (max)
Motional Capacitance (min)
Series Resistance (max)
Spurious Response (max)
make up the equivalent capacitance difference.
o
C ± 2
o
C ; Drive Level = 0.5 mW
Table 35: Isolation Transformers
Value
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
Table 36: Reference Crystal
Value
25.00000
4**
≤ ±50 per IEEE 802.3 requirement
Parallel Resonance, Fundamental Mode
10
10
60
> 5 dB below main within 500 kHz
Condition
@ 10 mV, 10 kHz
@ 1 MHz (min)
0 - 65 MHz
78Q8430 Data Sheet
Units
MHz
pF
PPM
pF
pF
Ω
83