CPC5622 Datasheet, PDF (12/18 Pages) Clare, Inc. – LITELINK® III Phone Line Interface IC (DAA)

CPC5622
The recommended components in the application
circuits yield a gain 0.26 dB at 2000 Hz. Clare
Application Note AN-117 Customize Caller ID Gain and
Ring Detect Voltage Threshold is a spreadsheet for trying
different component values in this circuit. Changing
the CID gain will also change the ringing detection
threshold and the timing of the polarity reversal
detection pulse, if used.
For single-ended receive applications where only one
RX output is used, the snoop circuit gain can be
adjusted back to 0 dB by changing the value of the
snoop series resistors R6, R7, R44 and R45 from
1.8MΩ to 715kΩ. This change results in negligible
modification to the ringing detect threshold.
3.3 Off-Hook Operation: OH=0
3.3.1 Receive Signal Path
Signals to and from the telephone network appear on
the tip and ring connections of the application circuit.
Receive signals are extracted from transmit signals by
the LITELINK two-wire to four-wire hybrid then
converted to infrared light by the receive path LED.
The intensity of the light is modulated by the receive
signal and coupled across the electrical isolation
barrier by a reflective dome.
On the low voltage side of the barrier, the receive
signal is converted by a photodiode into photocurrent.
The photocurrent, a linear representation of the
receive signal, is amplified and converted to a
differential voltage output on RX+ and RX-.
Variations in gain are controlled to within ±0.4 dB by
factory gain trim, which sets the output to unity gain.
To accommodate single-supply operation, LITELINK
includes a small DC bias on the RX+ and RX- outputs
of 1.0 Vdc. Most applications should AC couple the
receive outputs as shown in Figure 5.
LITELINK may be used for differential or single-ended
output as shown in Figure 5. Single-ended use will
produce 6 dB less signal output amplitude. Do not
exceed 0 dBm referenced to 600 Ω (2.2 V_P-P) signal
output level with the standard application circuits. See
application note AN-157, Increased LITELINK III Transmit
Power for more information.
Figure 5. Differential and Single-ended Receive
Path Connections to LITELINK
Low-Voltage Side CODEC
or Voice Circuit
LITELINK
RX+
RX-
0.1μF
RX+
0.1μF
RX-
RX
0.1μF
RX+
3.3.2 Transmit Signal Path
Transmit signals from the CODEC to the TX+ and TX-
pins of LITELINK should be coupled through
capacitors as shown in Figure 6 to minimize dc offset
errors. Differential transmit signals are converted to
single-ended signals within LITELINK then coupled to
the optical transmit amplifier in a manner similar to the
receive path.
The output of the optical amplifier is coupled to a
voltage-to-current converter via a transconductance
stage where the transmit signal modulates the
telephone line loop current. As in the receive path, the
transmit gain is calibrated at the factory, limiting
insertion loss to 0 ±0.4 dB.
Differential and single-ended transmit signals into
LITELINK should not exceed a signal level of 0 dBm
referenced to 600 Ω (or 2.2 V_P-P). For output power
levels above 0dBm consult the application note
AN-157, Increased LITELINK III Transmit Power for more
information.
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