STLC3065 datasheet(10/27 Pages) STMICROELECTRONICS

10 / 27 page

As already mentioned the metering pulse echo

cancellation is obtained by means of two external

components (RTTX and CTTX) that should match

the line impedance at the TTX frequency. This

simple network has a double effect:

Synthesise a low output impedance at the

TIP/RING pins at the TTX frequency.

Cut the eventual TTX echo that will be trans-

ferred from the line to the TX output.

Ringing

DET

DET1

DET2

0/1

@fr

RTrip

line 1+2

disable

0/1

@fr

RTrip

line 2

disable

0/1

@fr

RTrip

line 1

disable

When this mode is selected STLC3065 self gen-

erate an higher negative battery (-70V typ.) in or-

der to allow a balanced ringing signal of typically

62Vpeak.

The SLIC core is set in ring mode via the control

inputs D0 and D1 set respectively to 0 and 1.

In this condition both the DC and AC feedback

loop are disabled and the SLIC core line drivers

operate as voltage buffers.

The ring waveform is obtained toggling the D2 con-

trol bit at the desired ring frequency. This bit in fact

controls the line polarity (0=direct; 1=reverse).

As in the ACTIVE mode the line voltage transition

is performed with a ramp transition, obtaining in

this way a trapezoidal balanced ring waveform

(see fig.6).

The shaping is defined by the CREV external

capacitor.

Selecting the proper capacitor value it is possible

to get different crest fattor values. The following

table shows the crest factor values obtained with

a 20Hz and 25Hz ring frequency and with 1REN.

This value are valid either with European or USA

specification:

CREV

CREST

FACTOR

@20Hz

CREST

FACTOR

@25Hz

22nF

1.2

1.26

27nF

1.25

1.32

33nF

1.33

Not significant (*)

(*)Distorsion already less than 10%.

CTTX1

CTTX2

RLV

SQTTX

BURST

CKTTX

SHAPING

GENERATOR

Square wave pulse metering

Sinusoidal wave

pulse metering

RTTX

FTTX

Low Pass Filter

OP1

CFL

Required external components vs. filter order.

Figure 5. Metering pulse generation circuit.

Order CFL

THD

13%

XXX

GND

TIP

RING

dV/dT set

by CREV

2.5V typ.

65V

typ.

VBAT

2.5V typ.

Figure 6. TIP/RING typical ringing waveform

STLC3065

10/27

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