CPC5620 Datasheet, PDF (12/18 Pages) Clare, Inc. – LITELINK III Phone Line Interface IC (DAA)

INTEGRATED CIRCUITS DIVISION
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
1.8M to 715k 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. Next, the
receive signal is converted to infrared light by the
receive photodiode amplifier and 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.
CPC5620/CPC5621
On the equipment’s low voltage side of the barrier, the
receive signal is converted by a photodiode into a
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 outputs of 1.0V_DC.
Most applications should AC couple the RX outputs as
shown in Figure 4.
LITELINK may be used for differential or single-ended
output as shown in Figure 4. Single-ended use will
produce 6 dB less signal output amplitude. Do not
exceed 0 dBm into 600  (2.2 V_P-P) signal input with
the standard application circuit. See application note
AN-157, Increased LITELINK III Transmit Power for more
information.
Figure 4. Differential and Single-ended Receive Path Connections to LITELINK
Low-Voltage Side CODEC
or Voice Circuit
LITELINK
RX+
RX-
0.1µF
0.1µF
RX+
RX-
RX
0.1µF
RX+
3.3.2 Transmit Signal Path
Connect transmit signals from the low-voltage side
equipment to the TX+ and TX- pins of LITELINK. Do
not exceed a signal level of 0 dBm in 600  (or 2.2
V_P-P). Differential transmit signals are converted to
single-ended signals in LITELINK. The signal is
coupled to the transmit photodiode amplifier in a
similar manner to the receive path. See application
note AN-157, Increased LITELINK III Transmit Power for
more information.
The output of the photodiode 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,
gain is set to unity at the factory, limiting insertion loss
variation to ±0.4 dB.
Differential and single-ended transmit signals into
LITELINK should not exceed a signal level of 0 dBm
referenced to 600  (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.
12
www.ixysic.com
R05