ATTL7554BP Agere Systems, ATTL7554BP Datasheet - Page 22

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

L7554 Low-Power SLIC
Applications
dc Applications
Adjusting dc Feed Resistance
The dc feed resistance may be adjusted with the help of
Figure 28.
Figure 28. Equivalent Circuit for Adjusting the dc
Adjusting Overhead Voltage and dc Feed
Resistance Simultaneously
The following paragraphs describe the independent set-
ting of the overhead voltage and the dc feed resistance.
If both need to be set to customized values, combine
the two circuits as shown in Figure 29.
Figure 29. Adjusting Both Overhead Voltage and dc
22
22
–5 V
Rdc
R2
R1
R3
Feed Resistance
=
Feed Resistance
=
113
113
R1
R3
(continued)
DCOUT
DCR
25 k
+
(continued)
+
DCOUT
500
DCR
500
25 k
30%
--------------------
--------------------------------- -
R
V
30%
3
V
D C O U T
R
+
D C R
1
R
1
25 k
25 k
12-2560 (C)
12-2561 (C)
This is an equivalent circuit for adjusting both the dc
feed resistance and overhead voltage together.
The adjustments can be made by the simple superposi-
tion of the overhead and dc feed equations:
When selecting external components, select R1 on the
order of 5 k to minimize the programming inaccuracy
caused by the internal 25 k resistor. Lower values can
be used; the only disadvantage is the power consump-
tion of the external resistors.
Loop Range
The equation below can be rearranged to provide the
loop range for a required loop current:
Off-Hook Detection
The loop closure comparator has built-in longitudinal
rejection, eliminating the need for an external 60 Hz fil-
ter. This applies in both powerup and low-power scan
states. The loop-closure detection threshold is set by
resistor R
on-hook condition (I
V
goes low when V
ative:
R
LCTH
L
Rdc
= 0.05 mA x R
ITR
Figure 30. Off-Hook Detection Circuit
R
V
V
R
R
P
P
O H
LCTH
LCTH
LCTH
R
=
L
=
. Referring to Figure 30, NLC is high in an
(k ) = 2.5 x I
PR
PT
113
=
= 0.05 mA x R
= 0.05 x R
6.5
LCTH
--------------------------- -
V
+
B A T
TR
–
LCTH
+
20
crosses zero and then goes neg-
+
= 0, V
I
0.05 mA
500
L
–
--------------------------------------------- -
R
. The off-hook comparator
V
LCTH
–0.125 V/mA
2
TR
R
O H
+
DCOUT
(mA)
1
Lucent Technologies Inc.
R
---------------------------------- -
R
LCTH
– 0.125 V/mA x I
–
1
25 k
3
2R
R
+
= 0), and
25 k
1
+ V
R
P
1
+
–
–
25 k
DCOUT
Rdc
March 1997
25 k
R
Data Sheet
3
R
3
LCTH
NLC
DCOUT
TR
12-2553.a (C)
R
LCTH