stlc3075 STMicroelectronics, stlc3075 Datasheet - Page 12

• Manufacturer Part Number: stlc3075
• Description: Integrated Pots Interface For Home Access Gateway And Wll
• Manufacturer: STMicroelectronics

Functional description
3.2.4
12/36
ideal TTX echo cancellation), the metering pulse level on the line equals 1.33 or 2.66 times
the level applied to the RTTX pin.
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:
●
●
Ringing
When this mode is selected, the STLC3075 self generates a higher negative battery
(-70V typ.) in order to allow a balanced ringing signal of typically 65V peak.
In this condition both the DC and AC feedback loops are disabled and the SLIC line drivers
operate as voltage buffers. The ring waveform is obtained by toggling the D2 control 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
CREV external capacitor.
Figure 7.
Selecting the proper capacitor value it is possible to get different crest factor values.
The following table shows the crest factor values obtained with a 20Hz and 25Hz ring
frequency and with 1REN. These value are valid either with European or USA specification:
Table 5.
1. Distortion already less than 10%
The ring trip detection is performed by sensing the variation of the AC line impedance from
on-hook (relatively high) to off-hook (low). This particular ring trip method allows to operate
without DC offset superimposed on the ring signal and therefore obtaining the maximum
possible ring level on the load starting from a given negative battery.
It should be noted that such a method is optimized for operation on short loop applications
and may not operate properly in the case of long loop applications (> 500 ).
it synthesizes a low output impedance at the TIP/RING pins at the TTX frequency
it cuts the eventual TTX echo that would have been transferred from the line to the TX
output
CREV
TIP/RING typical ringing waveform
CREST factor values @ 20 and 25Hz
22nF
27nF
33nF
GND
VBAT
TIP
RING
dV/dT set
by CREV
CREST factor @20Hz
2.5V typ.
2.5V typ.
1.25
1.33
1.2
Figure 7
65V
typ.
). The shaping is defined by the
CREST factor @25Hz
Not
1.26
1.32
(1)
STLC3075