Datasheet

DS2155
156 of 238
24.8 Recommended Circuits
Figure 24-3. Software-Selected Termination, Metallic Protection
T2
2:1
75/100/110/120 Ω
S2
F1
60 Ω60 Ω
1:1
S1
0.1 µF
S3
T1
1.0 µF
F2
S4
T3
1
T4
1
TTIP
DV SS
Dallas Semiconductor
T1/E1/J1 SCT or LIU
TRING
DV DD
TV SS
TV DD
RV SS
RV DD
0.01 µF
2
0.1 µF
2
0.1 µF
2
0.1 µF
2
VCC
68 µF
2
VCC
RTIP
RRING
VCC
1
Choke is optional but should be included when necessary f or common mode noise reduction.
2
Decoupling capacitors need to be placed near dev ice power pins
Design Notes:
Tw isted Pair/Coax
75/100/110/120 Ω
Tw isted Pair/Coax
Table 24-A. Component List (Software-Selected Termination, Metallic
Protection)
NAME DESCRIPTION
F1 and F2 1.25A slow blow fuse
S1 and S2 25V (max) transient suppressor
S3 andS4 77V (max) transient suppressor
T1 and T2 Transformer 1:1CT and 1:2CT (3.3V, SMT)
T3 and T4 Dual common-mode choke (SMT)
Note 1:
T3 and T4 are optional. For more information, contact the Telecom Support Group at
[e-mail]
.
Note 2:
The layout from the transformers to the network interface is critical. Traces should be at least 25
mils wide and separated from other circuit lines by at least 150 mils. The area under this portion
of the circuit should not contain power planes.
Note 3:
Some T1 (never in E1) applications source or sink power from the network-side center taps of
the Rx/Tx transformers.
Note 4:
A list of transformer part numbers and manufacturers is available by contacting
[e-mail]
.