cx28250 Mindspeed Technologies, cx28250 Datasheet - Page 195

• Manufacturer Part Number: cx28250
• Description: Cx28250 Atm Physical Interface Phy Devices
• Manufacturer: Mindspeed Technologies

CX28250
ATM Physical Interface (PHY) Devices
28250-DSH-002-C
A.2 CX28250 to 5 V PMD Inputs
When connecting the CX28250 3.3 V PECL outputs to 5 V PECL inputs, ensure
that the lines are properly terminated. In addition, the input voltage levels must be
shifted. Both can be accomplished by the circuits in
differential for the PMD.
The termination impedance is given by:
The outputs of the CX28250 need to be biased near V
Furthermore, V
where: V
Using the values:
R
R
R
V
results in:
V
V
V
These values are well within the desired ranges and provide adequate voltage
oh
3
4
5
ih
il
ref
= 75 Ω
= 52 Ω
= 82.5 Ω
= 3.03 V
= 3.52 V
= 2.5 V
= 1.968 V
Mindspeed Technologies
oh
is the high level output from the CX28250 and:
ih
and V
V
il
ih
going to the PMD are given by:
V
V
Z
=
ref
il
0
(
---------------------------------------- -
=
=
V
=
cc
(
------------------------------------- -
(
(
----------------------------------- -
(
(
----------------------------------- -
(
R
R
R
R
R
–
R
3
3
3
3
3
V
3
V
+
+
+
+
™
+
oh
+
cc
R
R
R
R
R
R
)
4
4
4
4
4
×
×
4
)
)
)
+
+
R
+
×
×
R
R
5
R
R
4
V
R
5
5
cc
5
+
5
)
)
)
V
Appendix A PECL Applications
Figure
oh
A.2 CX28250 to 5 V PMD Inputs
ref
A-3.
(2.0 V). Therefore:
A-3