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CPC5620_1 Datasheet, PDF (12/17 Pages) Clare, Inc. – LITELINK® III Phone Line Interface IC (DAA)
CPC5620/CPC5621
signal and coupled across the electrical isolation
barrier by a reflective dome.
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 1.0VDC.
Most applications should AC couple the RX 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 into 600 Ω (2.2 VP-P) signal input with
the standard application circuit. 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 Ω (or 2.2 VP-P). For output power
levels above 0dBm consult the application note
AN-157, Increased LITELINK III Transmit Power for more
information.
Figure 6. Differential and Single-ended Transmit
Path Connections to LITELINK
Low-Voltage Side CODEC or
Transmit Circuit
LITELINK
TXA1
TXA2
0.1µf TX-
-
0.1µf TX+
+
Figure 5. 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 Ω (or 2.2
VP-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.
Low-Voltage Side CODEC or
Transmit Circuit
LITELINK
TXA1
0.1µf TX-
-
0.1µf TX+
+
3.4 Start-up Requirements
OH must be de-asserted (set logic high) once after
power-up for at least 50ms to transfer internal gain
trim values within LITELINK. This would be normal
operation in most applications. Failure to comply with
this requirement will result in transmission gain errors
and possibly distortion.
3.5 DC Characteristics
The CPC5620 and CPC5621 are designed for
worldwide application, including use under the
requirements of TBR-21. The ZDC, DCS1, and DCS2
pins control the VI slope characteristics of LITELINK.
Selecting appropriate resistor values for RZDC (R16)
and RDCS (R15) in the provided application circuits
assure compliance with DC requirements.
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