ATTL7554BP Agere Systems, ATTL7554BP Datasheet - Page 26

• Manufacturer Part Number: ATTL7554BP
• Description: L7554 Low-Power SLIC
• Manufacturer: Agere Systems

L7554 Low-Power SLIC
Applications
ac Design
Example 1, Real Termination
The following design equations refer to the circuit in
Figure 32. Use these to synthesize real termination
impedance.
Termination Impedance:
Receive Gain:
Transmit Gain:
Hybrid Balance:
To optimize the hybrid balance, the sum of the currents
at the VFX input of the codec op amp should be set to
0. The following expressions assume that the test net-
work is the same as the termination impedance.
26
26
g
h
rcv
g
g
z
b a l
z
rcv
tx
g
t
t
t x
=
=
=
=
=
=
(continued)
=
v
--------- -
v
--------- -
--------- -
v
–
2R
v
v
20
T R
------------------------------------------------------------------ -
T R
T R
------- -
R
f r
g s x
i
R
1
t r
hbal = 20log
log
T 2
P
X
+
(continued)
+
R
-----------
R
80
-------- -
R
R CV
--------- -
Z
R
400
T 1
T R
H B
X
+
+
–
R
----------- -
---------------------------------- -
1
R
gtx g
8
R C V
+
G P
V
------------
Vfr
-------- -
R
R
gsx
3200
G P
T 1
r c v
1
+
+
----------- -
R
R
--------- -
Z
R C V
z
T R
T 1
t
Example 2, Complex Termination:
For complex termination, the spare op amp is used
(see Figure 33).
The hybrid balance equation is the same as in
Example 1.
PCB Layout Information
Make the leads to BGND and V
for thermal and electrical reasons. Also, maximize the
amount of PCB copper in the area of—and specifically
on—the leads connected to this device for the lowest
operating temperature.
When powering the device, ensure that no external
potential creates a voltage on any pin of the device that
exceeds the device ratings. In this application, some of
the conditions that cause such potentials during pow-
erup are the following: 1) an inductor connected to PT
and PR (this can force an overvoltage on V
the protection devices if the V
and 2) inductance in the V
with the V
overvoltage).
This device is normally used on a circuit card that is
subjected to hot plug-in, meaning the card is plugged
into a biased backplane connector. In order to prevent
damage to the IC, all ground connections must be
applied before, and removed after, all other connec-
tions.
gtx
grcv
z
t
=
R
=
=
=
H B
BAT
–
---------- -
R
2R
2R
R
--------------------------------------------------------------------------- -
T6
1
X
=
filter capacitor to cause a destructive
P
P
+
--------------------
gtx g
+
+
R
------------- -
----------
Z
400
R
80
80
T/R
RCV
R
T3
X
+
+
rcv
+
---------
R
Z
R
------------- -
---------------------------------- -
1
T5
k Z
T4
R
8
BAT
RCV
+
GN
-------- -
R
T5
R
BAT
lead (this could resonate
Lucent Technologies Inc.
3200
G N
T 3
BAT
1
connection chatters)
+
+
as wide as possible
----------- -
R
----------
Z
R
z
R C V
T/R
T 3
t
March 1997
Data Sheet
---------
R
Z
BAT
T5
T4
through