Preliminary Data Sheet
October 2001
Low-Cost Ringing SLIC
L9214A/G
28
Agere Systems Inc.
Supervision
(continued)
Power Ring
(continued)
The ring signal will appear balanced on tip and ring.
That is, the ring signal is applied on both tip and ring,
with the signal on tip 180
°
out of phase from the signal
on ring. This operation is shown in Figure 12 below.
Ringing loop range is calculated as follows:
V
RINGLOAD
= {(V
BATTERY
–
4)/Crest Factor} *
{R
LOAD
/(R
LOAD
+ R
LOOP
+ 2 x R
PROTECTION
)}
As a practical example, calculate the maximum dc loop
length, assuming the following conditions:
Minimum required ring voltage = 40 Vrms
V
BATTERY
=
–
67 V
Trapezoidal ringing, crest factor = 1.2
Protection resistors = 30
each
Ring Load = 2 North American REN = 3500
+ 16
μ
F
Ringing frequency = 25 Hz
First, calculate the equivalent ringing load resistance at
25 Hz.
R
LOAD
= {(3500
)
2
+ (2 *
π
* 25 * 16E
–
6)
–
2
}
0.5
R
LOAD
= 3522
40 Vrms = {(67
–
4)/1.2)} {3522
/(R
LOOP
+ 3522
+
60
)}
R
LOOP
= 1040
Effects such as power supply tolerance and crest factor
tolerance can affect this calculation.
Crest factor is estimated by the formula:
Where:
f = ringing frequency; C
FB
= (C
FB1
+ C
FB2
)/2;
Ics = 30
μ
A with B3 = 1 and 90
μ
A with B3 = 0;
V
OHH
= 4 V
1
I
CS
×
-----------------------------------------------------------------------------------------
3
–
-------------------------------------------------------------------------------------------------------
=
12-3532.B (F)
Figure 12. Ring Operation
GND
V
BAT
RING
LOAD
1/2 R
LOOP
+ R
PROTECTION
1/2 R
LOOP
+ R
PROTECTION
PT
+1
PR
B1
SQUARE WAVE OR
PWM SIGNAL
L9214
V
TIP
V
RING
–
1
3 V
1 V