Data Sheet
March 1997
L7554 Low-Power SLIC
Example 2, Complex Termination:
Applications (continued)
ac Design (continued)
For complex termination, the spare op amp is used
(see Figure 33).
Example 1, Real Termination
3200
Z T5
---------
RT4
zt = 2RP + 80 Ω+
(
)
-----------------------------------
1 +
RT3
R T3
The following design equations refer to the circuit in
Figure 32. Use these to synthesize real termination
impedance.
+
-------- -----------
RGN RRCV
= 2RP + 80 Ω+ k(ZT5)
Termination Impedance:
8
v
–itr
T ⁄ R
grcv = ---------------------------------------------------------------------------
zt =
----------
RRCV R RCV
zt
RX
1 + ------------- + ------------- 1 + ----------
RHB =
--------------------
gtRxT×3grcvRGN
ZT/R
3200
z t = 2RP + 80 Ω+
----------------------------------
1 +
–RX 400 Z T5
RT1
R T1
gtx =
×
×
---------- ---------- ---------
+
-------- -----------
RT6
ZT/R RT4
RGP RRCV
The hybrid balance equation is the same as in
Example 1.
Receive Gain:
v
T ⁄ R
----------
vfr
grcv =
PCB Layout Information
8
g rcv =
------------------------------------------------------------------
RRCV R RCV
zt
Make the leads to BGND and VBAT as wide as possible
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.
1 +
+
1 +
----------- -----------
----------
ZT ⁄ R
RT1
RGP
Transmit Gain:
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 VBAT through
the protection devices if the VBAT connection chatters)
and 2) inductance in the VBAT lead (this could resonate
with the VBAT filter capacitor to cause a destructive
overvoltage).
vgsx
g tx =
----------
v
T ⁄ R
RX
400
g tx =
×
------- ----------
RT2 ZT ⁄ R
Hybrid Balance:
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.
V gsx
Vfr
------------
hbal = 20log
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.
RX
hbal = 20log
– gtx × grcv
--------
RHB
26
Lucent Technologies Inc.
AGERE [ AGERE SYSTEMS ]
