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STLC30R81

– Selecting Rxin+/Rxin- (first path), the sinusoidal waveform can be applied in differential mode (using

both inputs) or single ended mode (connecting one of the two input pins directly to the GND). This signal

comes from STLC5048 or other Codec

– Selecting Rg+/Rg- (second path), the sinusoidal (or PWM) waveform ringing, can be applied in differ-

ential mode (using both inputs) or single ended mode (connecting one of the two input pins directly to

the GND). The ring source (codec, waveform generators) can be always active and shared by multiple

lines.

Both DC/AC feedback loops are disabled except for the first path (Rxin+/Rxin-) that remains enabled. This func-

tionality will be managed through an "Input Word" that allows the ringing signal, to flow through the line. The

Table 3 shows how to select the proper input word.

Table 3. Control Word

Figure 5. Ringing internal block

In On-Hook condition, Tip and Ring are biased at -VBAT2/2; the input signal is typically amplified at 35dB.

Ring trip detection is performed sensing the variation of the AC line impedance from High (On-Hook) to Low

(Off-Hook). This particular ring trip method, allows to operate without DC offset superimposed on the ring signal

and therefore, obtain the maximum possible load driving capability, from a given negative battery. After Ring/

Trip detection, DET pin is set Low and remains latched keeping the STLC30R81 in Stand-by mode until the op-

erative mode is modified by Input Word.

PWM Ringing Waveform

A pulse-width modulated (PWM) signal may be used to provide the ringing input to Rg inputs. The signal is ap-

plied through a low-pass filter and AC-coupled into Rg+. This approach gives a sine wave output at tip and ring-

ing circuit.

Control Word

Input Selected Mode

D0

D1

D2

D3

1

0

0

1

Rxin+/ Rxin- Input selected

1

0

1

1

Rg+/Rg- Input selected

Logic interface

Rxin+

Rxin-

Rg+

Rg-

D0 D1 D2 D3

DET

OpAmp 1

OpAmp 2

Internal switch

Ring

Gain

Ring Trip

+

-

Ring

Det