STLC3065 查看數據表（PDF） - STMicroelectronics
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STLC3065 Datasheet PDF : 27 Pages
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STLC3065
Moreover the power available at Vbat is control-
led by the DC/DC converter that limits the peak
current drawn from the Vpos supply. The maxi-
mum allowed current peak is set by the RSENSE
resistor and it is typically 900mApk.
AC CHARACTERISTICS
The SLIC core provides the standard SLIC trans-
mission functions:
Input impedance synthesis: can be real or
complex and is set by a scaled (x50) external
ZAC impedance.
Transmit and receive: The AC signal present
on the 2W port (TIP/RING) is transferred to the
TX output with a -6dB gain and from the RX in-
put to the 2W port with a 0dB gain.
2 to 4 wire conversion: The balance imped-
ance can be real or complex, the proper can-
cellation is obtained by means of two external
impedance ZA and ZB.
Once in Active mode (D1=1) the SLIC core can
operate in different states setting properly D0 and
D2 control bits (see also Table3).
D0 D1 D2
Operating state
0 1 0 Active Normal Polarity
0 1 1 Active Reverse Polarity
1 1 0 Active TTX injection (N.P.)
1 1 1 Active TTX injection (R.P.)
POLARITY REVERSAL
The D2 bit controls the line polarity, the transition
between the two polarities is performed in a ”soft”
way. This means that the TIP and RING wire ex-
change their polarities following a ramp transition
(see fig.4). The transition time is controlled by an
external capacitor CREV. This capacitor is also
setting the shape of the ringing trapezoidal wave-
form.
Figure 4. TIP/RING typical transition from
Direct to Reverse Polarity
GND
TIP
4V typ.
dV/dT set
by CREV
RING
40V typ
ON-HOOK
When the control pins set battery reversal the line
polarity is reversed with a proper transition time
set via an external capacitor (CREV).
METERING PULSE INJECTION (TTX)
The metering pulses circuit consist of a burst
shaping generator that gives a square wave
shaped and a low pass filter to reduce the har-
monic distortion of the output signal.
The metering pulse is obtained starting from two
logic signals:
CKTTX: is a square wave at the TTX fre-
quency (12 or 16KHz) and should be perma-
nently applied to the CKTTX pin or at least for
all the duration of the TTX pulse (including ris-
ing and decay phases).
D0: enable the TTX generation circuit and de-
fine the TTX pulse duration.
This two signals are then processed by a dedi-
cated circuitry integrated on chip that generate
the metering pulse as an amplitude modulated
shaped squarewave (SQTTX) (see fig.5).
Both the amplitude and the envelope of the
squarewave (SQTTX) can be programmed by
means of external components. In particular the
amplitude is set by the two resistors RLV and the
shaping by the capacitor CS.
The waveform so generated is then filtered and
injected on the line. The low pass filter can be ob-
tained using the integrated buffer OP1 connected
between pin FTTX (OP1 non inverting input) and
RTTX (OP1 output) (see fig.5) and implementing
a ”Sallen and Key” configuration.
Depending on the external components count it is
possible to build an optimised application de-
pending on the distortion level required. In par-
ticular harmonic distortion levels equal to 13%,
6% and 3% can be obtained respectively with
first, second and third order filters (see fig.5).
The circuit shown in the ”Application diagram” is
related to the simple first order filter.
Once the shaped and filtered signal is obtained at
RTTX buffer output it is injected on the TIP/RING
pins with a +6dB gain.
It should be noted that this is the nominal condi-
tion obtained in presence of ideal TTX echo can-
cellation (obtained via proper setting of RTTX and
CTTX). In addition the effective level obtained on
the line will depend on the line impedance, the
protection resistor value and the series switch
(SW1 or SW2) on resistance.
In the typical application (TTX line impedance
=200Ω , RP=41Ω, SW1,2 on resistance = 9Ω and
ideal TTX echo cancellation) the metering pulse
level on the line will be 1.33 times the level ap-
plied to the RTTX pin.
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