HC5517 Intersil Corporation, HC5517 Datasheet - Page 13

• Manufacturer Part Number: HC5517
• Description: 3 REN Ringing SLIC For ISDN Modem/TA and WLL
• Manufacturer: Intersil Corporation

NOTE: During Ringing, the SHD output will be active for both on-hook and off-hook conditions. The AC current, for the on-hook condition, exceeds
the SHD threshold of 12mA. Valid off-hook detection during ringing is provided by the RTD output only.
Operation of the Battery Switch
The battery switch is used to select between the off-hook
battery of -24V and the ringing/standby battery of -80V.
When T
is off and the -24V battery is supplied to the SLIC through
D
flows through the collector of T
When D
respect to the drain (-80V) and T
connects the -80V battery to the SLIC through D
turn reverse biases D
Transhybrid Balance
The purpose of the transhybrid circuit is to remove the
receive signal (V-REC) from the transmit signal (V-XMIT),
thereby preventing an echo on the transmit side. This is
accomplished by using an external op amp (usually part of
the CODEC) and by the inversion of the signal from the
SLIC’s 4-wire receive port (V
transmit port (OUT1).
The external transhybrid circuit is shown in Figure 10. The
effects of capacitors C
fore omitted from the analysis. The input signal (V-REC) will
be subtracted from the output signal (V-XMIT) if I
are equal and opposite in phase. A node analysis yields the
following equation:
The value of R
Given that OUT1 is equal to -1/3 of V-REC (Equation 16) and
V-REC is equal to VTR (A
then R
be achieved by using 1% resistors values.
R
V REC
-------------------- -
10
2
–
R
=
. When T
2
BATTERY
SWITCH
–
2
R
-24V
-24V
-24V
-24V
-80V
-80V
-80V
-80V
1
9
+
= 3R
3
is off (battery switch is logic low) the MOSFET T
OUT1
---------------- -
turns on, the gate of the MOSFET is positive with
R
V REC
-------------------- -
OUT1
3
–
3.
1
2
A transhybrid balance greater than 30dB can
is on (battery switch is logic high) current
is then:
=
0
10
5
F1
, C
0
0
1
1
0
0
1
1
, isolating the two supplies.
7
4-Wire-2-Wire
and C
72
TABLE 2. HC5517 APPLICATION CIRCUIT OPERATING MODES SUMMARY
(Voice Signal)
1
RX
RC
3
8
turning on the zener D
0
1
0
1
0
1
0
1
) to the SLIC’s 4-wire
are negligible and there-
turns on. Turning T
= 1, Equation 15),
On-Hook Standby
Off-Hook Active
1
Power Denial
Power Denial
7
equals I
. This in
(EQ. 36)
(EQ. 37)
Ringing
MODE
Invalid
Invalid
Invalid
3
on
9
3
2
HC5517
.
Transhybrid Balance
Transhybrid balance of the pulse metering signal is
accomplished in 2 stages. The first stage uses the SLIC’s
internal op amp to invert the phase of the pulse metering sig-
nal. The second stage sums the inverted pulse metering sig-
nal with the incoming signal for cancellation in the
transhybrid amplifier. A third network can be added to offset
both tip and ring by the peak amplitude of the pulse metering
signal. This will allow both the maximum voice and pulse
metering signals to occur at the same time with no distortion.
Pulse Metering
Pulse metering or Teletax is used outside the United States
for billing purposes at pay phones. A 12kHz or 16kHz burst
is injected into the 4-wire side of the SLIC and transmitted
across the tip and ring lines from the central office to the pay
phone. For more information about pulse metering than cov-
ered here reference application note AN9608 “Implementing
Pulse Metering for the HC5509 Series of SLICs”.
DETECTORS VALID
FIGURE 10. TRANSHYBRID CIRCUIT (VOICE SIGNAL)
(Note)
SHD
HC5517
SIGNAL
PHASE
OF AC
SHIFT
180
-
+
RTD
SUMMING NODE CANCELS OUT
OUT GOING TRANSMISSION
INCOMING AC TRANSMISSION FROM
OUT1
V
-IN1
RX
C
8
R
R
APPLICATION CIRCUIT VALID
9
8
MTU
TRANSHYBRID CIRCUIT
C
R
I
R
(Pulse Metering)
7
2
3
2
EXTERNAL
C
I
5
1
R
-
+
1
AC TRANSMISSION
INCOMING
AC TRANSMISSION
CENTERING
V-XMIT
OUTGOING
V-REC