PCT2303N DATA SHEET
FUNCTIONAL DESCRIPTION
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functionality of the external components. In local analog
loopback mode, the AC’97 controller provides a digital
test waveform on SDATA_IN. This data is passed
across the isolation barrier, converted to analog,
internally looped to the receive path, converted to digital,
passed back across the isolation barrier, and presented
to the AC’97 controller. To enable local and analog
loopback, set L1B2:0 (L2B2:0) = 010. External analog
loopback mode allows the system to test external
components by passing converted data (from
SDATA_IN) to the transmit pin, which is looped
externally to the receive pin. To enable external analog
loopback, set L1B2:0 (L2B2:0) = 110. Both analog
loopback modes require power, which is typically
supplied by the loop current from Tip and Ring.
Charge Pump
The PCT303A has an integrated charge pump for 3.3 V-
only operation. The ISOcap requires a 5 V supply that
can come from either the VA pin or the internal charge
pump. For 3.3 V-only operation, R3 must not be
installed. The charge pump by default is set to be the 5 V
supply after the sample rate register is programmed. To
use a separate 5 V supply, connect 5 V through R3 and
set register 5Eh, bit 10 (PDC) to 1. The PDC must be set
before the sample rate register is written.
In-Circuit Testing
The PCT2303N’s advanced design provides the modem
manufacturer with increased ability to determine system
functionality during production line tests, as well as user
diagnostics. Several loopback modes exist allowing
increased coverage of system components.
The loopback mode allows the data pump to provide a
digital input test pattern on SDATA_IN and receive that
digital test pattern back on SDATA_OUT. To enable this
mode, set L1B2:0(L2B2:0)=101 in register 56h. In this
mode, the isolation barrier is actually being tested. The
digital stream is delivered across the isolation
capacitors, C1 and C2 to the line-side device and
returned across the same barrier.
The digital DAC loopback mode allows data to be sent
on the digital path from SDATA_IN to the digital section
of DAC to ADC to SDATA_OUT. This loopback mode is
used when the line-side chip is in power-down mode. To
enable this mode, set L1B2:0(L2B2:0) = 011 in
register 56h.
The remote analog loopback mode allows an external
device to drive the receive pins of the line-side chip and
receive the signal from the transmit pins. This mode
allows testing of external components connecting the
RJ-11 jack (Tip and Ring) to the line side of the
PCT303L. To enable this mode, set L1B2:0(L2B2:0) =
100 in register 56h.
The ADC loopback mode allows an external device to
drive the receive pins of the PCT303L. The signal is then
digitized on the PCT303L and sent to the PCT303A,
which sends the data back to the PCT303L. The signal
is then converted back to analog. The external device
receives the signal on the transmit pins. This mode
allows testing of the PCT2303N’s converters and
external devices between the PCT303L and RJ-11 jack.
To enable this mode, set the L1B2:0(L2B2:0) = 001.
The final two testing modes, local analog loopback and
external analog loopback, allow the system to test the
basic operation of the converters on the line side and the
PC-TEL, Inc.
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2303N0DOCDAT10A-0899
ETC [ ETC ]
