9/17

STLC30R81

Figure 7. Phone detection Diagram

Short Circuit

DET signal pin changes its logical level depending on the presence (or not) of short circuit at the output of the

Line Card (See Tab.5).

Table 5. Short Circuit Detection

Loop back

The test is aimed at cheking detection and feeding circuitry functionalities as described in fig. 8. The external

resistor RLPCK is closed internally between TIP and RING and emulates the phone resistance. Starting from

ACTIVE mode, when loop back mode is selected DET pin will change its level.

If DET pin is low it means that detection and feeding circuits work properly. If DET remains high it means that a

failure has been detected.

Table 6. Loop Back Detection

Figure 8. loop back detection diagram

Protection Mode

Suggested protection circuit is based on programmable LCP1521S Trisil and the surge current is limited by the

in Power-down mode, DET and AL are set Low.

For external applications, two diodes 1N4148 are suggested (Pls. see application diagram).

Control Word

DET

D0

D1

D2

D3

Short Circuit

No Short Circuit

1

111

0

1

Control Word

DET

D0

D1

D2

D3

Good

Fail

0

011

0

1

T>4ms

Active R.P.

HiZ

DET

Phone

T<2ms

DET

No Phone

Loop Back

DET

Active

Active