L3000N datasheet(10/32 Pages) STMICROELECTRONICS

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4) AUTOMATIC STAND - 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 functional circuit activated in this

mode.

When the off-hook condition occurs RING wire

voltage goes high (from - 48V to - 24V).

The output of the comparator C1 will go high set-

ting the output of the flip - flop FF high.

Therefore L3092 will set L3000N in Stand-by pro-

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-hook con-

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 VREF value the C2 comparator will 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-By mode).

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 operating in the limiting

current region of the DC characteristic, see fig. 1

and 2. GDK output will be set to 1 if the SLIC is

operating in the resistive region.

The SLIC will work in one of the two region de-

pending on the loop resistance and the pro-

grammed limiting current value.

By changing the liming current value selected in

conversation mode it is possible to measure the

Loop Resistance and therefore the line lenght

connected to the SLIC.

The following table shows the ranges of the loop re-

sistance that set the GDK output pin to high and

low level in correspondance of all the possible limit-

ing current values (25/40/60mA) with RFS = 200

Ω.

Figure 5: Off-hook Detection Circuit in Automatic Standby Mode

L3000N

L3000N - L3092

10/32

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