HC5517 Intersil Corporation, HC5517 Datasheet - Page 9

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

Therefore to match the HC5517, with R
600 load:
and:
To prevent loading of the V
are typically scaled by a factor of 100:
Since the impedance matching is a function of the voltage
gain, scaling of the resistors to achieve a standard value is
recommended.
For complex impedances the above analysis is the same.
Reference application note AN9607 (“Impedance Matching
Design Equations for the HC5509 Series of SLICs”) for the
values of KR
impedances.
Tip-to-Ring Open-Circuit Voltage
The tip-to-ring open-circuit voltage, V
programmable to meet a variety of applications. The design
of the HC5517 defaults the value of V
The HC5517 application circuit overrides the default V
operation when operating from a -80V battery. While operat-
ing from a -80V battery, the SLIC will be in either the ringing
mode or on-hook standby mode. In the ringing mode, V
designed to switch from 0V (centering voltage) to -47V
(Maintenance Termination Unit voltage). The centering volt-
age is active during the ringing portion of the ringing wave-
form and the Maintenance Termination Unit (MTU) voltage is
active during the silent portion of the ringing signal. In the
on-hook standby mode, the application circuit is designed to
maintain V
Centering Voltage Application Circuit Overview
The centering voltage is used during ringing to center the
DC outputs of the tip feed and ring feed amplifiers. Centering
the amplifier outputs allows for the maximum undistorted
voltage swing of the ringing signal. Without centering, the
output of each amplifier would saturate at ground or V
minimizing the ringing capability of the HC5517. The
required centering voltage, V
from a -80V battery.
Centering Voltage Application Circuit Operation
The circuit used to generate the centering voltage is shown
in Figure 5.
R
R
KR
KR
V
OC
9
8
8
9
=
=
=
=
8R
R
V
L
40k
40k
BAT
– R
S
4
OC
=
S
8 50
–
9
at the MTU voltage.
=
8
and KR
600
KR
KR
9
8
=
–
=
=
400
8
200
40k
100 Resistive 200
for several worldwide Typical line
TX
68
C
output, the value of R
=
, is +1.8V
400
OC
OC
–
S
DC
to:
, of the HC5517 is
equal to 50 , to a
when operating
+
Reactive
------------------------- -
100
8
(EQ. 26)
(EQ. 23)
(EQ. 24)
(EQ. 25)
and R
OC
BAT
OC
is
9
HC5517
,
The circuitry within the dotted lines is internal to the
HC5517. The value of the resistor designated as R is 108k
and the resistor R/20 is 5.4k . The tip amplifier gain of
20V/V amplifies the +1.8V
the internal 4V
amplifier output. The -40V
amplifier, adding to the battery voltage, achieving -40V at the
ring amplifier output.
Centering Voltage Design Equations
The centering voltage (V
voltage. A battery voltage of -80V requires a +1.8V
centering voltage. The equation used to calculate the
centering voltage is shown below.
The DC voltage at the outputs of the centered tip and ring
amplifiers can be calculated from Equation 28 and
Equation 29.
The shunt resistor of the divider network, R
determined from a design equation. It is selected based on
the trade-off of power dissipation in the voltage divider (low
value of R
(high value of R
1.0k
used to calculate the value of R
as follows:
V
V
V
C
TC
RC
FIGURE 5. CENTERING VOLTAGE APPLICATION CIRCUIT
TF
RF
=
=
=
and 2.0k . The application circuit design equation
–
V
-------------- -
V
BAT
BAT
20V
2
18
RING FEED
AMPLIFIER
AMPLIFIER
TIP FEED
) and loading affects of the internal R/20 resistor
C
+
–
90k
+
4
20V
18
R
DC
4
+
-
-
+
). The suggested range of R
20
C
offset, generating -40V
+
RC
4
DC
90k
90k
DC
C
R/20
R
R/2
+2V
) is dependent on the battery
24
at V
offset also sums into the ring
+5V
19
+
-
C
V BAT
---------------- -
to +36V
of the divider network is
2
T
TO ZENER
DIODE D
R
2
19
V
RING
DC
V
11
C
DC
18
and adds it to
D
18
is between
at the tip
6
, is not
(EQ. 27)
(EQ. 28)
(EQ. 29)
R
D
18
13
DC