HC5517_00 Datasheet, PDF (12/19 Pages) Intersil Corporation – 3 REN Ringing SLIC For ISDN Modem/TA and WLL

HC5517
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.
CADENCED
WAVEFORM
BATTERY ^-80V
SWITCH
-24V
RC
CENTERING
VOLTAGE
OFF ON OFF ON OFF ON OFF
MTU
ON OFF ON OFF ON OFF ON
FIGURE 8. RINGING WAVEFORM AND CONTROL SIGNALS
Ringing Design Equations
The differential tip to ring voltage during ringing, as a
function of REN, can be approximated from Equation 35.
V_TR(R_L) ≅ 2 × ^V--₅---^R_.--₄--^I--_e^N---₃-^G-- – -⁽--⁰---^.--⁷---⁰₍---₁-²--₀--⁾--₈⁽--²-_e---⁰-₃--⁰--₎--⁾_R--^V---_L--^T---^R----^O--- • 108e3
(EQ. 35)
The voltage V_RING is defined as the RMS amplitude of the
input ringing signal. V_TRO is the open circuit tip to ring
differential output voltage, calculated as V_RING multiplied by
the differential gain of 40V/V. The REN impedance is shown
as R_L. Figure 9 shows the relationship of REN load to
maximum differential tip to ring RMS voltage during ringing.
The maximum ringing signal amplitude herein assumes an
infinite 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.
47.00
46.00
45.00
44.00
43.00
42.00
41.00
40.00
39.00
1 REN
2 REN
3 REN
4 REN
5 REN
FIGURE 9. MAXIMUM RINGING OUTPUT VOLTAGE
(V_RING = 1.2V_RMS)
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
electronic data. The HC5517 application circuit is designed
to maintain 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
communications, 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.
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