78Q2123/78Q2133 MicroPHY™
10/100BASE-TX Transceiver
ISOLATION TRANSFORMERS
Two simple 1:1 isolation transformers are required at the line interface. Transformers with integrated common-
mode chokes are recommended for exceeding FCC requirements. This table gives the recommended line
transformer characteristics:
NAME
Turns Ratio
VALUE
1 CT : 1 CT ± 5%
350 µH (min)
0.40 µH (max)
25 pF (max)
0.9 Ω (max)
0.4 dB (typ)
CONDITION
Open-Circuit Inductance
Leakage Inductance
Inter-Winding Capacitance
D.C. Resistance
Insertion Loss
@ 10 mV, 10 kHz
@ 1 MHz (min)
0 - 65 MHz
HIPOT
1500 Vrms
Note: 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 MR19.15:14.
REFERENCE CRYSTAL
If the internal crystal oscillator is to be used, a crystal with the following characteristics should be chosen:
NAME
Frequency
VALUE
25.00000
UNITS
MHz
Load Capacitance*
Frequency Tolerance
Aging
4**
±50
±2
±5
pF
PPM
PPM/yr
PPM
Temperature Stability ( 0 - 70oC)
Oscillation Mode
Parallel Resonance, Fundamental Mode
Parameters at 25oC ± 2oC ; Drive Level = 0.5 mW
Drive Level (typ)
50-100
10
10
µW
pF
pF
Ω
Shunt Capacitance (max)
Motional Capacitance (min)
Series Resistance (max)
60
Spurious Response (max)
> 5 dB below main within 500 kHz
* Equivalent differential capacitance across the XTLP/XTLN pins.
** If crystal with a larger load is used, external shunt capacitors to ground should be added to make up the
equivalent capacitance difference.
Page: 34 of 42
© 2009 Teridian Semiconductor Corporation
Rev 1.5
TERIDIAN [ TERIDIAN SEMICONDUCTOR CORPORATION ]
