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參數(shù)資料
| 型號： | HC5517CM |
| 廠商： | HARRIS SEMICONDUCTOR |
| 元件分類： | 模擬傳輸電路 |
| 英文描述： | 3 REN Ringing SLIC For ISDN Modem/TA and WLL |
| 中文描述： | TELECOM-SLIC, PQCC28 |
| 文件頁數(shù)： | 10/18頁 |
| 文件大小： | 175K |
| 代理商： | HC5517CM |
69
where: V
D13
forward drop of D
13
, 0.63V.
V
D6
forward drop of D
6
, 0.54V.
R
18
is the shunt resistor of the divider, 1.1k
.
R
IN
is the input impedance of V
RING
, 5.4k
.
V
C
is the required centering voltage, 1.8V, V
BAT
= -80V.
V
CC
is the +5V supply.
Centering Voltage Logic Control
The pnp transistor T
2
is used to defeat the voltage divider
formed by R
19
, R
18
, D
13
and D
6
. When T
2
is off (RC is logic
high), +5V
DC
is divided to produce +1.8V
DC
at the V
RING
input. When T
2
is on (RC is logic low), its emitter base volt-
age of +0.9V
DC
is divided resulting in +0.2V at the anode of
D
6
, hence reverse biasing the diode (D
6
) and floating the
V
RING
pin.
MTU Voltage Application Circuit Overview
According to Bellcore specification TR-NWT-000057, an
MTU
voltage
may
be
required
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.
by
some
operating
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
RDC
, is a
function of the internal V
BAT
/2 reference and external zener
diode D
11
. When the magnitude of V
BAT
/2 is less than the
zener voltage, the zener is off and the input to the ring feed
amplifier is V
BAT
/2. When the magnitude of V
BAT
/2 is
greater than the zener voltage, the zener conducts and
clamps the noninverting terminal of the ring amplifier to the
zener voltage.
Internal to the HC5517 are connections to the tip feed amplifier
output and V
BAT
/2 reference. The DC voltage at the tip feed
output, V
TDC
, is a constant -4V during on-hook standby.
MTU Voltage Design Equations
The following equations are used to predict the DC output of
the ring feed amplifier, V
RDC
.
Where V
Z
is the zener diode voltage of D
11
and V
CE
and
V
BE
are the saturation voltages of T
2
. Using Equations 31
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
OC
as a function of battery voltage. The
graph illustrates the clamping function of the zener circuitry.
MTU Voltage Logic Control
The same pnp transistor, T
2
, that is used to control the
centering voltage is also used to control the MTU voltage.
The application circuit uses T
2
to ground or float the anode
of the zener diode D
11
. When RC is a logic low (T
2
on) the
anode of D
11
is referenced to ground through the collector
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
2
off) the anode of D
11
floats,
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
R
19
V
-----------------------------+
V
C
V
IN
V
–
–
–
(
)
R
18
V
C
R
18
R
IN
(
)
D6
=
(EQ. 30)
FIGURE 6. RING FEED AMPLIFIER CIRCUIT CONNECTIONS
+
-
TIP FEED OUTPUT
V
REF
3
RING FEED
AMPLIFIER
RF
90K
90K
90K
D
11
C
16
T
2
+5V
RC
V2
R
19
R
24
V
--------------
V
Z
<
V
RDC
2
V
--------------
4
+
=
(EQ. 31)
V
--------------
V
Z
≥
V
RDC
2
V
–
Z
V
CE
V
BE
–
(
)
+
(
)
4
+
=
(EQ. 32)
V
--------------
V
Z
<
V
OC
V
TDC
2
V
--------------
4
–
–
=
(EQ. 33)
V
--------------
V
Z
≥
V
OC
V
TDC
2
V
–
Z
V
CE
V
BE
–
(
)
+
(
)
4
–
–
=
(EQ. 34)
T
O
+50
+40
+30
+20
+10
0
-16
-28
-40
-52
-58
-68
-80
FIGURE 7. V
OC
AS A FUNCTION OF BATTERY VOLTAGE
HC5517
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