L9217A Datasheet, PDF (21/30 Pages) Agere Systems – Low-Cost Line Interface with Reverse Battery and PPM

Data Sheet
November 2001
L9217A/G Low-Cost Line Interface
with Reverse Battery and PPM
Applications (continued)
dc Applications (continued)
Ring Trip Detection
The ring trip circuit is a comparator that has a special input section optimized for this application. The equivalent
circuit is shown in Figure 15, along with its use in an application using unbalanced, battery-backed ringing.
PHONE
HOOK SWITCH
RLOOP
RTSP
RTSP +
RC PHONE
VBAT VRING
2.94 MΩ
RS
402 Ω/510 Ω
RTSN
NSTAT
IP = IN
CRTS1
+ 8.6 V
0.015 µF
IN ^–
–
3.32 MΩ/3.40 MΩ ^{RTSN 15 kΩ}
Figure 15. Ring Trip Equivalent Circuit and Equivalent Application
2799 (F)
Ring trip detection threshold is given by the following equation:
ITH (mA) = ^[---^R-----^T-----^S----^N------⁽--^M------^Ω-----⁾----⁺-----⁰-_[---^.R-⁰----_T1----^5S-----^–_N-----^R₍---_M--^T----_Ω^S-----^P₎----₊-⁽--^M--₀----_.^Ω-₀----₁-⁾--^]-₅---^×-_]---_×-^[---^V-_R----^B-_S---^A---^T------^–----⁸----^.--⁶----^]----^×----¹----⁰----⁰----⁰--
Longitudinal Balance
The SLIC is graded to certain longitudinal balance specifications. The numbers are guaranteed by testing (Figure 5
and Figure 8). However, for specific applications, the longitudinal balance may also be determined by termination
impedance, protection resistance, and especially by the mismatch between protection resistors at tip and ring. This
can be illustrated by the following equation:
LB
=
20
x
log
----⁽--³----⁶---⁸------⁺----^R------^P-----⁾---^×-----⁽--³----⁶----⁸-----⁺-----^Z----^T------^–----^R------^P-----⁾---
368 × (2 × [ZT – 2 × RP] × ∆ + ε)
where:
LB: longitudinal balance.
RP: protection resistor value in Ω.
ZT: magnitude of the termination impedance in Ω.
ε: protection resistor mismatch in Ω.
∆: SLIC internal tip/ring sensing mismatch.
The ∆ can be calculated using the above equation with these exceptions: ε = 0, ZT = 600 Ω, RP = 100 Ω, and the
longitudinal balance specification on a specific code.
Now with ∆ available, the equation will predict the actual longitudinal balance for RP, ZT, and ε.
Be aware that ZT may vary with frequency for complex impedance applications.
Agere Systems Inc.
21