hc55183. Intersil Corporation, hc55183. Datasheet - Page 18

• Manufacturer Part Number: hc55183.
• Description: Extended Reach Ringing Slic Family
• Manufacturer: Intersil Corporation

Additional Application Diagrams
Reducing Overhead Voltages
The transmission overhead voltage of the device is internally
set to 4V per side. The overhead voltage may be reduced by
injecting a negative DC voltage on the receive input using a
voltage divider (Fig. 19). Accordingly, the 2-wire port overload
level will decrease the same amount as the injected offset.
The divider shunt resistance is the parallel combination of
the internal 160k resistor and the external R
R
additional power dissipation of the divider. The DC gain
relationship from the divider voltage, V
outputs is shown below.
With a low battery voltage -24V and a divider voltage of
-0.5V, the Tip to Ring voltage is 17V. As a result, the
overhead voltage is reduced from 8V to 7V and the overload
level will decrease from 3.5V
CODEC Ringing Generation
Maximum ringing amplitudes of the device are achieved with
signal levels approximately 2.4V
receive output of the CODEC may serve as the low level ring
generator. The ringing input impedance of 480k minimum
should not interfere with CODEC drive capability. A single
external capacitor is required to AC coupled the ringing
signal from the CODEC. The circuit diagram for CODEC
ringing is shown below.
Implementing Teletax Signalling
A resistor, R
injecting the teletax signal (Figure 20). For most
applications the synthesized device impedance (i.e., 600 )
V
1
T R
and R
–
HC5518X
=
1:1
FIGURE 19. EXTERNAL OVERHEAD CONTROL
1:1
V
2
FIGURE 20. CODEC RINGING INTERFACE
BL
should be greater than 500k to minimize the
T
HC5518X
–
, is required at the -IN input of the device for
8
160 k
–
2 V
480K
160 k
+
-
D
VRX
PEAK
45
VRS
VRX
HC55180, HC55181, HC55182, HC55183, HC55184
VBL
P-P
R
V
R
D
2
1
to 3.0V
. Therefore the low pass
C
RX
D
, to the Tip and Ring
PEAK
2
RX OUT
CODEC
FROM
CODEC
. The sum of
.
(EQ. 38)
will not match the 200 teletax impedance. The gain set by
R
to the teletax injection point. Therefore the device appears
as a low impedance source for teletax. The resistor R
calculated using the following equation.
The signal level across a 200 load will be twice the injected
teletax signal level. As the teletax level at VTX will equal the
injection level, set R
is based on the voice band transhybrid balance
requirements. The connection of the teletax source to the
transhybrid amplifier should be AC coupled to allow proper
biasing of the transhybrid amplifier input
Ringing With DC Offsets
The balanced ringing waveform consists of zero DC offset
between the Tip and Ring terminals. However, the linear
amplifier architecture provides control of the DC offset
during ringing. The DC gain is the same as the AC gain,
40V/V per amplifier. Positive DC offsets applied directly to
the ringing input will shift both Tip and Ring away from half
battery towards ground and battery respectively. A voltage
divider on the ringing input may be used to generate the
offset (Figure 22). The reference voltage, V
either the CODEC 2.4V reference voltage or the 5V supply.
An offset during ringing of 30V, would require a DC shift of
15V at Tip and 15V at Ring. The DC offset would be created
by a +0.375V (V
should be selected to minimize the value of the AC coupling
capacitor C
voltage reference. The ringing input impedance should also
be accounted for in divider resistor calculations.
R
T
T
VFB
cancels the impedance matching feedback with respect
=
HC5518X
------------------------------------------------------------------ -
200
CFB
RT
FIGURE 22. EXTERNAL OVERHEAD CONTROL
+
RS
2 R
TELETAX
SOURCE
FIGURE 21. TELETAX SIGNALLING
-IN
480K
and the loading of the ring generator and
200
D
P
+
-
) at the VRS input. The divider resistors
+
-
+
RS
TA
C
R
S
VTX
= R
400
VRS
B
for cancellation. The value of R
R
V
R
R
REF
S
B
C
R
V
R
D
2
1
R
C
F
RS
REF
+2.4V
, can be
-
+
FROM
RING GEN.
TX IN
CODEC
(EQ. 39)
T
is
B