Obsolete Product(s) - Obsolete Product(s)
Concerning AC characteristic the STLC30R80 al-
lows to set 2W termination impedance by means of
one external scaled impedance that may be com-
plex. Two to four wire conversion is provided by an
external network. Such network can be avoided in
case of application with COMBOII, in this case the
two to four wire conversion is implemented inside
the COMBOII by means of the programmable Hy-
bal filter.
When in ACTIVE mode it is also possible to per-
form battery reversal in soft mode (with program-
mable transition time) without affecting the AC sig-
nal transmission.
Ringing
When ringing mode is selected, by toggling the
D2 pin is possible to insert the ringing signal on
the line: the ringing frequency is equal to the one
applied to the D2 pin. The ringing signal is a bal-
anced trapezoidal wave form where the TIP and
RING voltages switch continuously between GND
and VREG: VREG is obtained directly from VB1
(VREG = VB1 - 1.8V). The slope of the trapezoi-
dal wave form is set by the external Crev capaci-
tor and it allows to obtain ringing signal with dis-
tortion less than 10%: with a fine tuning of this
capacitor is possible to obtain distortion value
less than 5% (crest factor from 1.25 to 1.35).
The VB1 value must be higher enough (~70V) in
order to obtain ringing signals with more than
40Vrms. The VB2 battery is used only when the
line is in off hook and its value can be reduced
(typ. 24V) in order to minimize the power con-
sumption.
The ring trip detection is performed sensing the
variation of the AC line impedance from on-hook
(relatively high) to off-hook (relatively low). This
particularly ring trip method allows to operate
without DC off-set superimposed on the ringing
signal and therefore obtaining the maximum pos-
sible ring level on the load starting from a given
negative battery.
It should be noted that such a meted is optimized
for operation on short loop applications and may
not operate properly in presence of long loop
(>500 Ohm).
As the ring trip is detected the logic indicator
DET
is set low and the ringing is automatically discon-
nected without waiting for the card controller com-
mand (auto ring trip).
Ringing with high REN number
When ringing high number of REN, for example
5REN, or short loops, it could happen that the line
AC current, trigger the ring trip circuit producing
false ring trip.
If this happens, a proper SW resistor (Rswitch)
can be inserted between RLIM and the pin.
The effect of this resistor is to improve the AC
current capability in Ring mode avoiding false ring
trip in presence of high REN numbers (typ.
5REN) and short loop.
One side effect of Rswitch is to reduce ring trip
sensitivity in presence of long loops; therefore it is
recommended to adjust Rswitch properly check-
ing the correct behaviour of the device in the two
worst-case conditions:
- 0
Ω
loop, Max REN#
- Max loop length, 1 REN
The lower is the Rswitch value; the higher is the
immunity to false Ring trip, producing as side ef-
fect a lower Ring trip sensitivity on long loops.
The typical value of Rswitch is shown in the Ex-
ternal Components Table (pag.7.13)
High Impedance Feeding.
As Stand-By, this mode is set in On-Hook condi-
tion, with further reduced power consumption.
Higher power efficiency turns back a lower immu-
nity of the Off-Hook detector to line common
mode currents. The DC feeding shows a constant
current characteristic (I
lim
= 17mA) followed by a
resistive range with an equivalent series resis-
tance R
FEED
= 1600
Ω
+ 2Rp.
Thermal protection circuit is still active, preventing
the junction temperature, in case of fault condi-
tion, to exceed 150°C
In High Impedance Feeding most of the circuit is
switched off, only the circuit, dedicated to Off-
Hook detection, is powered. This allows to reduce
17mA
R
FEED
= 1600Ω +2R
P
D98TL373
V
BAT
-0.8V
I
V
Figure d. STLC30R80 DC Characteristic in
High Impedance Feeding
GND
TIP
RING
dV/dT set
by CREV
3V typ.
60V
typ.
VREG
3V typ.
Figure c. Typical ringing wave form.
STLC30R80
5/13
