LUCL8576BP-D AGERE [Agere Systems], LUCL8576BP-D Datasheet - Page 24

• Manufacturer Part Number: LUCL8576BP-D
• Description: Dual Ringing SLIC
• Manufacturer: AGERE [Agere Systems]

L8576B Dual Ringing SLIC
Applications
ac Design
Typically, values of 0.1 F to 0.47 F capacitors are
used for dc blocking. The addition of blocking capaci-
tors will cause a shift in the return loss and hybrid bal-
ance frequency response toward higher frequencies,
degrading the lower-frequency response. The lower
the value of the blocking capacitor, the more pro-
nounced the effect is, but the cost of the capacitor is
lower. It may be necessary to scale resistor values
higher to compensate for the low-frequency response.
This effect is best evaluated via simulation. A PSPICE *
model for the L8576B is available.
Design equation calculations seldom yield standard
component values. Conversion from the calculated
value to standard value may have an effect on the ac
parameters. This effect should be evaluated and opti-
mized via simulation.
Use of an Auxiliary Battery Supply
A second lower-voltage battery supply can be used
with the L8576B in order to lower the overall power
consumption on a short-loop design. For long loops,
any power savings will be negated, since long loops
are supplied by the main battery voltage. The auxiliary
battery would be connected to pins 9 and 37 in lieu of
the R
are removed, more power will be dissipated in the SLIC
so internal SLIC power dissipation must be examined.
First, determine the auxiliary battery voltage:
The auxiliary battery should be set 8 V greater than the
maximum tip/ring loop voltage on the longest allowed
loop, when both channels are off-hook and in current
limit.
Aux Bat
Where:
I
R
V
TOL
For example, using the recommended 24 mA current
limit, an overhead voltage of 8 V, and a maximum loop
length of 550 , the maximum auxiliary battery voltage
is 23.3 V.
24
24
LIM
OH
LOOP
= dc current limit set by R
VBAT
= overhead voltage.
PWR
= maximum loop resistance supported (tele-
(MAX)
phone plus line resistance plus protection
resistors).
= battery tolerance, for a battery tolerance of
resistors. When the external R
±5%, use 1.1.
= [(I
(continued)
LIM
(continued)
x R
LOOP
) + V
PROG
OH
(usually 0.024).
] TOL
PWR
VBAT
resistors
* PSPICE is a registered trademark of Cadence Design Systems, Inc.
Next, calculate the power dissipated in the SLIC:
Components of the SLIC power dissipation are quies-
cent power of V
ated with V
as follows:
W
W
nels.
W
nels.
W
x 2 channels.
Where:
4 V is the minimum overhead voltage, and 3 mA is
V
For example, substituting values from the data sheet:
V
I
V
I
Aux Bat
I
The following powers are calculated:
W
W
W
W
0.8106
The sum of the four powers is 1.822 W.
Finally, calculate the maximum ambient tempera-
ture allowed for the calculated power dissipation:
T
The L8576’s 44-pin PLCC exhibits a 43 °C/W thermal
resistance if in an enclosure with natural airflow. The
maximum operating temperature of the SLIC is 150 °C.
Thermal shutdown occurs typically at 160 °C.
For example:
T
The above scenario would allow operation up to 70 °C.
CC(Max)(quiescent)
BAT(Max)(quiescent)
LIM
A(max)
A(max)
BAT
CC
BAT(Max)
Aux Bat(loop current)
Aux Bat(loop current)
VCC(quiescent)
VBAT(quiescent)
VBAT(loop current)
VCC(quiescent)
VBAT(quiescent)
VBAT(loop current)
= 24 mA
’s contribution to loop current.
= 5 V
= T
= 150 – (43 x 1.822)
= 150 – 78.4
= 71.7 °C
(Max)
= –70 V
j
BAT
– (R
= –23.3 V
= V
= 5 x 0.0055 x 2 = 0.055
= |V
= |–70| x 0.004 x 2 = 0.56
and Aux Bat. These can be calculated
= 5.5 mA
CC
= (|V
= 4 mA
= (|–70| – 4) x 0.003 x 2 = 0.396
JA
CC
= (|Aux Bat
= (|–23.3| – 4) x (0.024 – 0.003) x 2 =
and V
BAT(Max)
x P
x I
BAT(Max)
DISS SLIC(max)
CC(Max)(quiescent)
BAT
| x I
| – 4 V) x 3 mA x 2 chan-
and loop current associ-
(Max)
BAT(Max)(quiescent)
| – 4 V) x (I
)
Agere Systems Inc.
x 2 channels.
May 2001
LIM
x 2 chan-
– 3 mA)