L9310 Datasheet, PDF (42/60 Pages) Agere Systems – Line Interface and Line Access Circuit Full-Feature SLIC,Ringing Relay,and Test Access Device

L9310 Line Interface and Line Access Circuit
Full-Feature SLIC, Ringing Relay, and Test Access Device
Data Sheet
July 2001
Special Functions
Periodic Pulse Metering (PPM)
Periodic pulse metering (PPM), also referred to as
TTX, is input to the PPMIN input of the L9310. Upon
application of appropriate logic control, this signal is
presented to the tip/ring subscriber loop. The state of
the L9310 may be changed while applying PPM sig-
nals. The L9310 assumes that a shaped PPM signal is
applied to the PPMIN input.
Sufficient drive current is available in the tip and ring
drive amplifiers to support 2.5 Vrms PPM signals into a
200 Ω load with a 70 mA dc current limit, and a 5 Vrms
PPM signal into a 200 Ω load with a 45 mA dc current
limit.
PPM input signals may be a maximum 1.25 V at
PPMIN. The gain from PPMIN to tip/ring is 10. Thus,
for 2.5 Vrms at tip and ring, apply a 0.25 Vrms signal at
PPMIN. The PPM signal should be ac coupled to
PPMIN through a 0.01 µF capacitor.
When applied to tip and ring, the PPM signal will also
be returned through the SLIC and will appear at the
SLIC VITR output. The concern is that this high-voltage
signal can overload the codec input and cause distor-
tion of the (desired) ac signal. Therefore, some sort of
PPM rejection scheme must be employed. Refer to
Figure 1, Architecture Diagram. The L9310 outputs pin
PPMOUT, which is the output of the PPM input ampli-
fier. Connecting a resistor, RPPM, from PPMOUT to
node ITR will provide a path for a hybrid reject of the
returned meter pulse signal. The return path from tip
and ring to VITR for the PPM signal is through the
internal AX amplifier. ITR is the input to this amplifier.
Through RPPM, by applying a PPM signal equal in mag-
nitude, but 180 degrees out of phase to the returned
PPM signal at ITR, the PPM signal is cancelled, pre-
venting overload at the codec input. Even if the cancel-
lation is not perfect, the idea is to reduce the PPM
signal so as not to overload the codec. Codecs typi-
cally have a low-pass filter at their input to reject any
residual meter pulse signal.
The value of RPPM is selected by:
RPPM =
[{(VPPMIN x 10)/(RPPMLOAD + Rdc + 2RP)}/324.5]^–1
In the case of very high meter pulse signals, such as
5 Vrms, the cancellation provided by resistor RPPM may
not be sufficient to prevent overload at the codec input.
In this case, additional filtering/rejection may be neces-
sary.
PPM injection can cause false loop closure indication.
Connect a 0.01 µF capacitor from this node LCF to VCC
to filter the loop closure detector. If loop closure filtering
is not required, leave LCF open.
Line Test
The L9310 provides line test capability. Through a
series of integrated analog switches, in the test mode,
an analog voltage proportional to the dc tip to ground
voltage, dc ring to ground voltage, the differential dc tip
to ring voltage may be generated at the SLIC
TESTLEV output. Additionally, an analog voltage pro-
portional to the dc tip to ground current, dc ring to
ground current, the differential dc tip to ring current
may also be generated at the SLIC TESTLEV.
Figure 2 shows the architecture of the integrated test
switches. The test switches are configured via the logic
input table to provide voltage measurements, tip to
ground, ring to ground, and tip to ring. A voltage that is
proportional to the ac tip/ring current appears at the
VITR output; thus, for ac current measurements, the
test switches apply the VITR output to the TESTLEV
output. A voltage that is proportional to the ac plus dc
tip/ring current appears at the VTX output; thus, for dc
current measurements, the test switches apply the VTX
output to the TESTLEV output, with TESTSIG input
grounded.
Differential tip to ring current is achieved via the logic
truth table. Additionally, individual control of the line
break switches allows tip to ground current measure-
ments (tip break switch closed, ring break switch open,
tip amp state) or ring to ground current measurements
(tip break switch open, ring break switch closed, ring
amp state).
An analog ac test tone may also be applied to a test
input TESTSIG. TESTSIG input is active upon entering
a test state and remains active until leaving the test
mode. Using this feature, a voltage proportional to ac
tip to ground voltage, ac ring to ground voltage, the dif-
ferential ac tip to ring, the ac tip to ground current, ac
ring to ground current, the differential ac tip to ring cur-
rent may also be generated at the SLIC TESTLEV. By
varying the frequency of the applied test tone, parame-
ters such as line capacitance may be measured.
If the codec can accommodate self-test features, the
L9310 can be configured to operate in this mode. Dur-
ing the test modes, the L9310 receive path is active;
thus, a test tone may be applied at the RCVN/RCVP
inputs, through the codec, via a PCM input. In this
mode of operation, couple TESTLEV, not VITR, to the
codec.
42
Agere Systems Inc.