RTL8208B-LF/RTL8208BF-LF
Datasheet
7.12. 1.8V Power Generation
The RTL8208B(F)-LF uses a PNP power transistor to generate 1.8V from the 3.3V power supply. This
1.8V provides for digital core and analog circuits. The 1.8V power generation circuit also uses an external
diode (1N4001) to reduce the voltage drop between the Emitter and Collector of the power transistor. If
your system needs more than one RTL8208B(F)-LF chip (greater than 8 ports), do not use one PNP
transistor for all of the RTL8208B(F)-LF chips, even if the rating is enough. Instead, use one transistor
for each RTL8208B(F)-LF.
Do not connect any beads directly between the collector of the PNP transistor and VDDA. This will affect
the stability of the 1.8V power significantly.
Figure 20. Using a PNP Transistor to Transform 3.3V Into 1.8V
Table 35. An Example Using Power Transistor 2SB1182
Parameter
Symbol
VCBO
VCEO
VEBO
IC
Limits
-40
-32
-5
-2
10
Unit
V
V
Collector-Base Voltage
Collector-Emitter Voltage
Emitter-Base Voltage
Collector Current
Collector Power
V
A (DC)
W
PC
Dissipation
Junction Temperature
Storage Temperature
Tj
Tstg
150
-55~+150
°C
°C
Note: Absolute maximum ratings (Ta=25°C).
For more information, refer to http://www.rohm.com
7.13. Cable Tester
The cable tester (UTP cable only) determines the quality of the cables, connectors, and terminations.
Some of the possible problems that can be diagnosed include open/short faults. The fault location can also
be identified.
The RTL8208B(F)-LF’s cable tester transmits a signal of known amplitude to one pair of an attached
cable. The transmitted signal will continue down the cable until it reflects off a cable imperfection. The
magnitude of the reflection and the time it takes for the reflection to come back are shown in registers.
Using the information in the registers, the distance to the problem location and the type of problem can be
determined.
Single-Chip Octal 10/100-TX/FX PHY Transceiver
47
Track ID: JATR-1076-21 Rev. 1.3
REALTEK [ Realtek Semiconductor Corp. ]
