HC5517 Intersil Corporation, HC5517 Datasheet - Page 12

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

CENTERING
the HC5517 application circuit meets the hazardous voltage
requirements of FCC Part 68.306 by forcing the MTU volt-
age. Without the zener clamping solution, a programmable
power supply would have to be designed. The intervals listed
in Table 1 would require the power supply to switch voltages
and settle to stable operation well within 100ms. The design
of such a power supply may prove quite a challenge. The
zener solution provides a cost effective, low impact to
meeting a wide variety of tip to ring open circuit voltages.
Ringing Design Equations
The differential tip to ring voltage during ringing, as a
function of REN, can be approximated from Equation 35.
The voltage V
input ringing signal. V
ential output voltage, calculated as V
differential gain of 40V/V. The REN impedance is shown as
R
mum differential tip to ring RMS voltage during ringing. The
maximum ringing signal amplitude herein assumes an infi-
nite source and sink capability of the tip feed and ring feed
amplifiers. Due to the amplifier output design, the HC5517 is
limited to 3 REN ringing capability for this reason.
WAVEFORM
CADENCED
V
L
FIGURE 8. RINGING WAVEFORM AND CONTROL SIGNALS
TR
BATTERY
VOLTAGE
. Figure 9 shows the relationship of REN load to maxi-
SWITCH
R
MTU
L
RC
2
-80V
-24V
RING
V
----------------- -
5.4e3
RING
OFF
ON
is defined as the RMS amplitude of the
–
TRO
---------------------------------------------------
OFF
ON
0.702 200 V
is the open circuit tip to ring differ-
108e3 R
71
OFF
ON
L
OFF
ON
TRO
RING
OFF
ON
108e3
multiplied by the
OFF
ON
(EQ. 35)
OFF
ON
HC5517
ON-HOOK STANDBY MODE
On-hook standby mode is with the phone on-hook (i.e., not
answered) and ready to accept an incoming voice signal or elec-
tronic data. The HC5517 application circuit is designed to main-
tain the MTU voltage during this mode of operation. During this
mode, the SHD output is valid and the RTD output is invalid.
OFF-HOOK ACTIVE MODE
Off-hook active accommodates voice and data communica-
tions, including pulse metering, with a battery voltage of
-24V. The MTU voltage during this mode is defeated by the
zener clamp design regardless of the state of RC. It is
important to have RC low to disable the ringing voltage.
Only the SHD output is valid during this mode.
POWER DENIAL MODE
The HC5517 will enter the power denial mode whenever F1
is a logic low. During power denial, the tip and ring amplifiers
are active. The DC voltages of both amplifiers are near
ground, resulting in a maximum loop current of 7mA. Both
the SHD and the RTD detector output are invalid.
Table 2 summarizes the operating modes of the HC5517
application circuit. The table indicates the valid detectors in
each mode as well as valid application circuit operation.
FIGURE 9. MAXIMUM RINGING OUTPUT VOLTAGE
47.00
46.00
45.00
44.00
43.00
42.00
41.00
40.00
39.00
1 REN
(V
RING
= 1.2V
2 REN
RMS
)
3 REN
4 REN
5 REN