LUCL9312AP-D AGERE [Agere Systems], LUCL9312AP-D Datasheet - Page 25

• Manufacturer Part Number: LUCL9312AP-D
• Description: Line Interface and Line Access Circuit Forward Battery SLIC and Ringing Relay for TR-57 Applications
• Manufacturer: AGERE [Agere Systems]

July 2001
Applications
dc Characteristics
Power Control Resistor (continued)
Again assume:
T
150 C – 85 C = 65 C
Allowed thermal rise =
package thermal impedance x SLIC power dissipation
65 C = 38 C/W x SLIC power dissipation
Allowed SLIC power dissipation (P
This time, assume a maximum ambient operating tem-
perature of 85 C, a maximum current limit of 45 mA
(including tolerance), and a maximum battery of –56 V.
Again, assume a (worst-case) minimum dc loop of 0
and that 50
the handset is 200 :
Total P
Total P
Total P
Again, the power dissipated in the SLIC is the total
power dissipation less the power that is dissipated in
the loop.
SLIC P
Loop power = (I
Loop power = (45 mA)
Loop power = 0.6075 W
SLIC power = 2.4375 W – 0.6075 W
SLIC power = 1.83 W > 1.5 W
Under these extreme conditions, thermal margin is
increased via an external power control resistor.
The power dissipated in the power control resistor is
calculated by:
P
where in this example:
P
V
V
V
Agere Systems Inc.
TSD
BAT
LOOP
ROH
PRW
PRW
= –52 V
– T
is the ring-side overhead voltage of the SLIC.
=
is power in the resistor
= I
D
D
D
D
AMBIENT(max)
= (56 V x 45 mA) + 0.100 W
= 2.34 W + 0.100 W
= 2.4375 W
= total power – loop power
LIM
----------------------------------------------------------------------
V
* (R
BAT
protection resistors are used. Assume
LIM
LOOP
–
)
(continued)
V
2
R
= allowed thermal rise
ROH
x (R
PWR
+ R
2
(continued)
x (0
–
LOOPdcmin
PROT
V
LOOP
)
+ 100
Forward Battery SLIC and Ringing Relay for TR-57 Applications
2
+ 2R
D
) = 1.71 W
P
+ 200
+ R
HANDSET
)
)
Since this device is dc unbalanced, the tip side over-
head will remain typically at –2 V and the ring side over-
head will vary with the voltage at V
ring default overhead of 5.5 V, the ring overhead is typi-
cally 3.5 V.
Overhead Voltage
Overhead is programmable in the active mode via an
applied voltage source at the device’s OVH control
input. The voltage source may be an external voltage
source or derived via a resistor divider network from
the V
programmable external voltage source may be used to
provide software control of the overhead voltage.
The overhead voltage (V
age by:
V
Overall accuracy is determined by the accuracy of the
voltage source and the accuracy of any external resis-
tor divider network used and voltage offsets due to the
specified input bias current. If a resistor divider from
V
accurate result due to a lower offset associated with
the input bias current; however, lower value resistors
will also draw more power from V
gramming resistors should be between 75 k and
200 k .
Note that a default overhead voltage of 5.5 V is
achieved by shorting input pin OVH to analog ground.
Internally, the SLIC needs typically 2 V from each sup-
ply rail to bias the amplifier circuitry. This can be
thought of as an internal saturation voltage.
The default overhead provides sufficient headroom for
on-hook transmission of a 3.14 dBm signal into 900
3.14 = 10 log
V = 1.36 V, which is required over and above the inter-
nal saturation voltage for signal swing.
1.36 V + 4 V = 5.36 V < 5.5 V default overhead; thus, a
3.14 dBm into 900
distortion.
The overhead voltage accuracy achieved will not only
be affected by the accuracy of the internal SLIC cir-
cuitry, but also by the accuracy of the voltage source
and the accuracy of any external resistor divider net-
work used.
OH
REF
= 5.5 V + 5 x V
REF
is used, lower magnitude resistor will give a more
SLIC output or an external voltage source. A
-------- -
0.9
V
2
OVH
signal is passed without clipping
(V)
OH
) is related to the OVH volt-
REF
OH
. The sum of pro-
. For the total tip/
25
.