RTL8208 Ver la hoja de datos (PDF) - Realtek Semiconductor
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RTL8208 Datasheet PDF : 40 Pages
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RTL8208
7.10 Polarity Detection and Auto Correction
For better noise immunity and lower interference to ambient devices, the Ethernet electrical signal on a twisted pair cable is
transmitted in differential forms. That is, the signal is transmitted on two wires for each direction with inverse polarities (+/-). If
wiring on the connector is faulty or a faulty transformer is used, the two inputs to a transceiver may carry signals with opposite
but incorrect polarities. As a direct consequence, the transceiver will not work properly.
When the RTL8208 operates in 10Base-T mode, it automatically reverses the polarity of its two receiver input pins if it detects
that the polarities of the incoming signals on the pins are incorrect. However, this feature is unnecessary when the RTL8208 is
operating in 100Base-TX mode.
7.11 2.5V Power Generation
The RTL8208 uses a PNP transistor to generate 2.5V from the 3.3V power supply. This 2.5V provides for digital core and analog
receive circuits. Once your system needs more than one RTL8208 chip (greater than 8 ports), do not use one PNP transistor for
all of the RTL8208 chips even if the rating is enough. Instead, use one transistor for each RTL8208.
Do not connect any beads directly between the collector of PNP transistor and VDDAL. This will affect the stability of the 2.5V
power significantly if the bead exists.
3.3V
3.3V
2SB1197K
Ic(max.)=800mA
47uF
2.5V
RTL8208 VDDAH
VCTRL
VDDAL
0.1uF
VDDAH: 3.3V
VDDAL: 2.5V
Using a PNP Transistor to Produce 2.5V
The power transistor is a 2SB1197K, and follows the following specifications.
Absolute maximum ratings (Ta=25°C)
Parameter
Symbol
Collector-base voltage
VCBO
Collector-emitter voltage
VCEO
Emitter-base voltage
VEBO
Collector current
IC
Collector power dissipation
PC
Limits
-40
-32
-5
-0.8
0.2
Unit
V
V
V
A(DC)
W
Junction temperature
Tj
150
°C
Storage temperature
Tstg
-55~+150 °C
For more information, refer to http://www.rohm.com
2003/04/04
31
Rev.1.97
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