L9214A/G
Low-Cost Ringing SLIC
Preliminary Data Sheet
October 2001
First, calculate the equivalent ringing load resistance at
25 Hz.
Supervision (continued)
Power Ring (continued)
RLOAD = {(3500 Ω)2 + (2 * π * 25 * 16E–6)–2}0.5
RLOAD = 3522 Ω
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.
40 Vrms = {(67 – 4)/1.2)} {3522 Ω/(RLOOP + 3522 Ω +
60 Ω)}
RLOOP = 1040 Ω
Ringing loop range is calculated as follows:
Effects such as power supply tolerance and crest factor
tolerance can affect this calculation.
VRINGLOAD = {(VBATTERY – 4)/Crest Factor} *
{RLOAD/(RLOAD + RLOOP + 2 x RPROTECTION)}
Crest factor is estimated by the formula:
1
As a practical example, calculate the maximum dc loop
length, assuming the following conditions:
-------------------------------------------------------------------------------------------------------
=
(4 × f × CFB × VBAT1 – VOHH )
-----------------------------------------------------------------------------------------
1 –
3 × ICS
Minimum required ring voltage = 40 Vrms
VBATTERY = –67 V
Where:
Trapezoidal ringing, crest factor = 1.2
Protection resistors = 30 Ω each
Ring Load = 2 North American REN = 3500 Ω + 16 µF
Ringing frequency = 25 Hz
f = ringing frequency; CFB = (CFB1 + CFB2)/2;
Ics = 30 µA with B3 = 1 and 90 µA with B3 = 0;
VOHH = 4 V
L9214
1/2 RLOOP + RPROTECTION
PT
PR
GND
1 V
+1
RING
SQUARE WAVE OR
PWM SIGNAL
VTIP
B1
VRING
LOAD
3 V
–1
VBAT
1/2 RLOOP + RPROTECTION
12-3532.B (F)
Figure 12. Ring Operation
28
Agere Systems Inc.
AGERE [ AGERE SYSTEMS ]
