
4) AUTOMATICSTAND - BY (ASB) MODE
This is an operating mode similar to the Power
Down Mode, but with the software procedure to
detect off-hook condition integrated in hardware
on chip.
Fig. 5 shows the functionalcircuit activated in this
mode.
When the off-hook condition occurs RING wire
voltage goes high (from - 48V to - 24V).
The output of the comparatorC1 will go high set-
tingthe output of the flip- flop FF high.
Therefore L3092 will set L3000S in Stand-bypro-
viding a ground signal at pin PDO.
At the same time the external capacitor CINT will
be slowly charged.
In Stand-by the internal off-hook Detection circuit
will be activated and will check if the off-hookcon-
dition detected by the comparator C1 was true or
not true.
If the off-hook condition is confirmed the SLIC will
be kept in Stand-by Mode and the output ONHK
will go low when CS is low.
If the off-hook condition is not confirmed the SLIC
will be kept in Stand - By only for a few seconds.
(typ. 5sec). When the voltage at CRT out put will
reach the V
REF
value the C2 comparatorwill reset
the FF Flip - Flop and therefore the SLIC will be
set again in Power Down.
The Automatic Stand-by (ASBY) Mode combine
the key characteristics of Power Down (PD) and
Stand-by (SBY) Modes in particular it is charac-
terized by a very low power consumption (as the
Power Down mode) and a sophisticated off hook
detection circuit (as the Stand-Bymode).
The card controller will receive the off-hook infor-
mation from the pin ONHK only after that it is
checked and confirmed by the internal off-hook
detector that is not sensitive to spikes and com-
mon mode line signal. Therefore the software re-
quired to manage the SLIC will be very simple.
5) TEST (TS)MODE
When this mode is activated the SLIC will be set
in conversation mode keeping the initial value of
limiting current.
The GDK output pin of L3092 Digital Interface will
be set to ”0” if the SLIC is operatingin the limiting
current region of the DC characteristic, see fig. 1
and 2. GDK output will be set to 1 if the SLIC is
operatingin the resistive region.
The SLIC will work in one of the two region de-
pending on the loop resistance and the pro-
grammedlimiting currentvalue.
By changing the liming current value selected in
conversation mode it is possible to measure the
Loop Resistance and therefore the line lenght
connectedto the SLIC.
Thefollowingtableshowsthe rangesof the loopre-
sistance that set the GDK output pin to high and
low level in correspondanceof all the possiblelimit-
ingcurrentvalues(25/40/60mA)with RFS= 200
.
Figure 5:
Off-hookDetection Circuit in AutomaticStandby Mode
L3000S
L3000S - L3092
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