STLC3080 datasheet(21/23 Pages) STMICROELECTRONICS

21 / 23 page

RS1 must be connected to the positive RR; RR

should be connected directly to the ringing gener-

ator as it is in the figure. The ratio between RS1

and RR must be chosen considering that there is

an offset current in the input stage equal to

7.5

µA. This offset has been introduced to take in

account the leackage current of the line.

In fig.D2 is shown the relation between the CRT

charging current ICRT and the line current ILINE.In

the range -30

µA<ICRT<+30µA ICRT is propor-

tional to ILINE while it remains limited to

±30µA

for higher value of ILINE. Consequently, in case of

short loops, the ring-trip detection time is inde-

pendent on the loop resistance, as the CRT

charging is performed at a fixed current. In case

of long loops the detection time will increase as

the ICRT decreases proportionally to the loop re-

sistance.

ICRT

ILINE

-30uA

+30uA

ILINEth=7.5mA(typ)

ILINEth=IthRS1/RR

(if RR=600

Ω and RS1=RS2=600KΩ)

Figure D2. relation between Icrt and Iline.

Vring=60Vrms @ f=25Hz

VB=-48Volt

DET

RING

wire

CRT

OFF_HOOK

RING-TRIP DETECTION

Figure D3. Ring Trip detection signals.

STLC3080

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