HC5517 Intersil Corporation, HC5517 Datasheet - Page 10

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

where: V
Centering Voltage Logic Control
The pnp transistor T
formed by R
high), +5V
input. When T
age of +0.9V
D
V
MTU Voltage Application Circuit Overview
According to Bellcore specification TR-NWT-000057, an
MTU voltage may be required by some operating
companies. The minimum allowable voltage to meet MTU
requirements is -42.75V, which is used by measurement
equipment to verify an active line. Also, some facsimile and
answering machines use the MTU voltage as an indication
that the telephone is on-hook or not answered. In addition to
the Bellcore specification, FCC Part 68.306 requires that the
maximum tip to ground or ring to ground voltage not exceed
-56.5V for hazardous voltage limitations. These two require-
ments have been combined and the resulting range is
defined as the MTU voltage. The HC5517 application circuit
can be programmed to any voltage within this range using
the zener clamping circuit.
MTU Voltage Application Circuit Operation
The circuit used to generate the MTU voltage is shown in
Figure 6.
The ring feed amplifier DC output voltage, V
function of the internal V
diode D
zener voltage, the zener is off and the input to the ring feed
amplifier is V
greater than the zener voltage, the zener conducts and
clamps the noninverting terminal of the ring amplifier to the
zener voltage.
R
6
RING
FIGURE 6. RING FEED AMPLIFIER CIRCUIT CONNECTIONS
19
RF
, hence reverse biasing the diode (D
=
--------------------------------------------------------------------------------------------------- -
pin.
V
R
R
V
V
RING FEED
AMPLIFIER
V
11
D13
D6
C
CC
18
IN
CC
. When the magnitude of V
DC
is the required centering voltage, 1.8V, V
is the input impedance of V
is the shunt resistor of the divider, 1.1k .
19
forward drop of D
–
is the +5V supply.
DC
forward drop of D
V
V
2
, R
is divided to produce +1.8V
90K
BAT
C
D13
is on (RC is logic low), its emitter base volt-
is divided resulting in +0.2V at the anode of
+
18
+
-
C
/2. When the magnitude of V
V
–
16
D6
, D
V
2
D6
13
is used to defeat the voltage divider
R
V
REF
IN
BAT
–
and D
V
+
C
3
/2 reference and external zener
69
V
90K
90K
6
C
13
, 0.54V.
R
D
6
R
18
11
. When T
18
, 0.63V.
TIP FEED OUTPUT
R
V
---------------- -
BAT
IN
BAT
2
RING
6
2
/2 is less than the
) and floating the
R
DC
is off (RC is logic
19
, 5.4k
at the V
T
+5V
BAT
RDC
2
BAT
(EQ. 30)
= -80V.
R
, is a
RING
24
/2 is
RC
HC5517
Internal to the HC5517 are connections to the tip feed amplifier
output and V
output, V
MTU Voltage Design Equations
The following equations are used to predict the DC output of
the ring feed amplifier, V
Where V
V
and 32, the tip-to-ring open-circuit voltage can be calculated
for any value of zener diode and battery voltage.
Figure 7 plots V
graph illustrates the clamping function of the zener circuitry.
MTU Voltage Logic Control
The same pnp transistor, T
centering voltage is also used to control the MTU voltage.
The application circuit uses T
of the zener diode D
anode of D
base junction of the transistor. Current then flows through
the zener, allowing the ring amplifier input to be clamped.
When RC is a logic high (T
inhibiting the clamping action of the zener.
HC5517 Modes of Operation
The four modes of operation of the HC5517 Ringing SLIC
are ringing, on-hook standby, off-hook active and power
denial. Three control signals select the operating mode of
V
-------------- -
V
-------------- -
V
-------------- -
V
-------------- -
BE
BAT
BAT
BAT
BAT
FIGURE 7. V
2
2
2
2
are the saturation voltages of T
+50
+40
+30
+20
+10
TDC
V
V
V
V
Z
0
-16
Z
Z
Z
Z
is the zener diode voltage of D
11
, is a constant -4V during on-hook standby.
BAT
is referenced to ground through the collector
OC
V
V
V
V
/2 reference. The DC voltage at the tip feed
OC
-28
RDC
RDC
OC
OC
AS A FUNCTION OF BATTERY VOLTAGE
11
as a function of battery voltage. The
=
=
=
=
. When RC is a logic low (T
V
V
RDC
2
2 V
TDC
TDC
-40
–
V
-------------- -
BAT
.
2
2
2
Z
–
–
2
, that is used to control the
2
2 V
off) the anode of D
+
to ground or float the anode
–
V
-------------- -
-52
V
+
BAT
CE
2
4
Z
+
2
–
. Using Equations 31
V
V
–
BE
CE
-58
4
11
–
+
V
and V
BE
4
-68
11
2
–
(EQ. 31)
(EQ. 32)
(EQ. 34)
(EQ. 33)
CE
4
on) the
floats,
and
-80