APPLICATION NOTES AND REFERENCE DIAGRAMS
S2070
needed for edge rate control or on long lines. These
43Ω resistors should be placed as close to the MAC
TBC output as possible.
Reference Designs
Figure 6 shows a reference design with a 5V MAC.
The TBC output of the MAC swings from 0-5 V. The
TBC input to the S2070 will not tolerate signals
above it’s VCC voltage rail, so the TBC signal swing
is reduced by using the voltage divider shown in Fig-
ure 7. The 43Ω series resistors on the TX and TBC
outputs of the MAC provide 50Ω termination (43Ω +
~7Ω output impedance) to dampen any reflections
coming from the S2070 inputs. Placing these resis-
tors on TX[0-9] is optional; they should be included if
Figure 7 shows the 3.3V reference design. Note that
there is no TBC voltage divider. Also, the Fiber Optic
transmitter and receiver may be either dc or AC
coupled.
Termination into the Fiber Optic transmitter is shown
as 100Ω line-line. Refer to the data sheet or applica-
tion notes of your FO transmitter of choice for input
connection recommendations.
Figure 6. Fibre Channel Application, 5.0V MAC
optional
S2070
(3.3V)
24
EN_CDET
/LCK_REF
EN_CDET
27
0.01µF
-LCK_REF
TX[0-9]
Fiber Optic
10
62
61
43Ω
43Ω
Transmitter
(5.0V PECL
Inputs)
TXP
TXN
TX[0-9]
150Ω
0.01µF
19
22
100Ω
EWRAP
EWRAP
180Ω
330Ω
TBC
TBC
150Ω
MAC
(5.0V)
10
RX[0-9]
RBCP
RX[0-9]
RBC1
30
31
47
0.01µF
Fiber Optic
54
52
RBCN
RBC0
RXP
RXN
Receiver
(5.0V PECL
Outputs)
330Ω
0.01µF
COM_DET
COM_DET
100Ω
14
RATEN
10K Ω
330Ω
July 8, 1999
5
AMCC [ APPLIED MICRO CIRCUITS CORPORATION ]
