AN2064 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'AN2064' PDF : 14 Pages View PDF
AN2064 - APPLICATION NOTE
Figure 3 shows the classical protection topology used to protect one section of an analog subscriber line
card. A first stage uses both series overcurrent protection devices (fuses or PTCs) and TRISIL protectors
(TRISIL 1, threshold voltage = +/- 270V for US) allowing the ring relay to be protected against full lightning
and power contact surges. A second level (TRISIL 2, threshold voltage = 0/-Vbat) allows the SLIC to be
fine tuned protected. The presence of longitudinal series resistors makes the current capability rate of this
TRISIL to be adjusted.
Figure 4: CO ADSL modem protection circuit
Tip
Ring
Fuse or PTC
ADSL CO Modem
TRISIL 1
TRISIL 1
Fuse or PTC
C
Transformer
TRISIL 2
Secondary protection Fuse or PTC and TRANSIL 1
Figure 4 shows the protection topology generally used to protect the ADSL modem (or line cards when
use of a line transformer). This modem is connected to the analog line card by means of a splitter stage
and then receives the same operating voltages. Please note that series resistors are generally not per-
mitted in such an application. Protection is provided by the TRISIL (TRISIL 1, threshold voltage = +/-
270V), which assumes the full lightning current while the series overcurrent protection devices (fuses or
PTCs) allow the module to be well protected against 50/60Hz power contact.
3. Series protection
As previously mentioned, the use of series overcurrent protection devices is mandatory to protect sub-
scriber line cards against 50/60Hz power contacts. As far as power contact is concerned, standards re-
quire the equipment to withstand several tests with different acceptance criteria. First level criterion for
US standards (or A criterion for European requirements) requires the equipment to be fully operational
after tests while second level (or B criterion) allows the system to be out of order but no fire or smoke is
permitted. Table 2 shows AC power fault requirements of the US Telcordia GR1089 standard.
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