CPC5710N Datasheet, PDF (7/9 Pages) Clare, Inc. – Phone Line Monitor (PLM) IC

3. Using CPC5710N
3.1 LIN/CMP Input
The LIN/CMP input selects the active output, either
the comparator output CMPOUT or the linear outputs,
LINOUT- and LINOUT+. Set LIN/CMP low for linear
output and high for comparator output. Note that both
outputs cannot be used at once.
With LIN/CMP at logic low (LIN/CMP = 0), the
amplifier outputs are biased at 1 Vdc and CMPOUT is
held high. With LIN/CMP at logic high (LIN/CMP = 1),
LINOUT+ is 0 V and LINOUT- is 2 V.
Figure 5. LIN/CMP Timing for Caller-ID Signal
Reception
2s 500 ms
3s
475 ms 2s
Caller ID data
LIN/CMP
Signal levels not to scale
3.2 Amplifier Design
Considerations
Amplifier inputs are biased at 1.25 Vdc, the internal
voltage references. The internal common-mode
circuitry maintains the average of the inputs at 1.25
Vdc. For example, if one input reaches 1.3 V, the
common-mode circuit drives the other input to 1.2 V.
3.2.1 Linear Amplifier Gain
Display feature information (caller ID) and voice
signals are coupled through the linear amplifier. In
North America, CID data signals are typically sent
between the first and second ringing signal burst.
Referring to Figure 4, signal gain from tip and ring to
LINOUT+ and LINOUT- is determined by:
CPC5710N
GAIN_CID(dB) = 20log -----------------------------------⁶---^R----^S---^N----^P---^D------------------------------------
(4R_SNP + R_SNPD)² + ₍---_π----_f--_C---¹-_S--_N----_P---₎--₂-
where ƒ is the frequency of the signal.
Clare Application Note AN-117 Customize Caller ID Gain
and Ring Detect Voltage Threshold is a spreadsheet for
trying different component values in this type of circuit.
3.3 Comparator Considerations
3.3.1 Ringing Signal Detection
The CPC5710N comparator is a full-wave
configuration. Ringing signals will assert the output on
positive and negative parts of the ringing waveform.
Hysteresis is employed in the internal comparator
circuit to provide noise immunity. The set-up of the
comparator causes CMPOUT output pulses to remain
low for most of the ringing signal positive and negative
half-cycles. CMPOUT returns high when the ringing
signal is near the zero-voltage crossing.
Figure 6. CMPOUT Relative to Ring Signal
Ring Signal
CMPOUT
3.3.2 Setting Ring Detection Threshold
The ring detection threshold depends on the
component values of the input network. The values for
these components shown in the typical application
circuits are recommended for typical operation.
Referring to Figure 4, the ring detection threshold can
be changed according to the following formula:
V_RINGPK
=


-_R-⁷--_R-⁵---⁰_S--_N-^m---_P--^V-_D--_
(4R_SNP + R_SNPD)² + ₍---_π----_f-_R----_I--_N---_G-¹---_C----_S---_N---_P---₎---₂
Rev. 1.0 12/16/2002
www.clare.com
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