LUCL9218AAR-D AGERE [Agere Systems], LUCL9218AAR-D Datasheet - Page 19

• Manufacturer Part Number: LUCL9218AAR-D
• Description: Low-Cost Line Interface
• Manufacturer: AGERE [Agere Systems]

Data Sheet
November 2001
Agere Systems Inc.
Applications
dc Applications
Battery Feed
The dc feed characteristic can be described by:
where:
I
V
|
V
R
R
R
The design begins by drawing the desired dc template.
An example is shown in Figure 13.
Notes:
V
I
R
L
LIM
V
BAT
dc1
T/R
OH
L
P
dc
= dc loop current.
BAT
= loop resistance, not including protection resistors.
= protection resistor value.
= 22 mA.
= SLIC internal dc feed resistance.
= 115 .
= –48 V.
= overhead voltage. This is the difference between
= dc loop voltage.
|
Figure 13. Loop Current vs. Loop Voltage
the battery voltage and the open loop tip/ring
voltage.
= battery voltage magnitude.
50
40
30
20
10
0
0
I
LIM
V
T/R
TESTED
I
10
L
(continued)
=
12.5 k
=
-------------------------------------------- -
1
--------------------------------- -
R
LOOP VOLTAGE (V)
V
R
L
V
B A T
20
L
+
B AT
+
2R
2R
–
–
P
V
P
V
+
O H
+
O H
R
30
R
dc
I
LIM
dc
R
ONSET
R
–1
dc1
L
40
12-3050 (F).i
50
Starting from the on-hook condition and going through
to a short circuit, the curve passes through the follow-
ing two regions:
Region 1: On-hook and low-loop currents. The slope
Region 2: Current limit. The dc current is limited to a
Current Limit
With the B0/B1 logic inputs set to 11 (low current limit),
current limit with a 100
equation:
0.637 R
The relationship between low current limit (B0 = 1,
B1 = 1) and high current limit (B0 = 1, B1 = 0) is
Overhead Voltage
In order to drive an on-hook ac signal, the SLIC must
set up the tip and ring voltage to a value less than the
battery voltage. The amount that the open loop voltage
is decreased relative to the battery is referred to as the
overhead voltage, expressed as the following equation:
Without this buffer voltage, amplifier saturation will
occur and the signal will be clipped. The L9218 is auto-
matically set at the factory to allow undistorted on-hook
transmission of a 3.14 dBm signal into a 900
impedance.
--------------------------------- -
I
I
LIMIT
LIMIT
High
Low
PROG
corresponds to the dc resistance of the
SLIC, R
voltage is the battery voltage minus the over-
head voltage of the device, V
cal). These values are suitable for most
applications but can be adjusted if needed.
starting value determined by external resis-
tor R
the gain from tip/ring to pin DCOUT.
L9218A/G Low-Cost Line Interface
= 0.7
(k ) + 2 mA= I
V
PROG
OH
dc1
= |V
, an internal current source, and
(70
BAT
load is given by the following
| – (V
typical). The open circuit
LIM
x (mA)
PT
– V
PR
OH
)
(6.5 V typi-
loop
19