CS8403A-CS CIRRUS [Cirrus Logic], CS8403A-CS Datasheet - Page 30

• Manufacturer Part Number: CS8403A-CS
• Description: 96KHZ DIGITAL AUDIO TRANSMITTER
• Manufacturer: CIRRUS [Cirrus Logic]

APPENDIX A: RS422 DRIVER
INFORMATION
The RS422 drivers on the CS8403A and CS8404A
are designed to drive both the professional and con-
sumer interfaces. The AES/EBU specification for
professional/broadcast use calls for a 110
impedance and a balanced drive capability. Since
the transmitter impedance is very low, a 110
sistor should be placed in series with one of the
transmit pins. (A 110
transformer would, with the receiver impedance of
110 , provide a 55
low.) The specifications call for a balanced output
drive of 2-7 volts peak-to-peak into a 110
with no cable attached. Using the circuit in Figure
A1, the output of the transformer is short-circuit
protected, has the proper source impedance, and
provides a 5 volt peak-to-peak signal into a 110
load. Lastly, the two output pins should be attached
to an XLR connector with male pins and a female
shell, and with pin 1 of the connector grounded.
In the case of consumer use, the specifications call
for an unbalanced drive circuit with an output im-
pedance of 75
0.5 volts peak-to-peak ±20% when measured
across a 75
shown in Figure A2 only uses the TXP pin and pro-
vides the proper output impedance and drive level
using standard 1% resistors. The connector for con-
sumer would be an RCA phono socket. This circuit
is also short circuit protected.
The TXP pin may be used to drive TTL or CMOS
gates as shown in Figure A3. This circuit may be
30
CS8403A/4A
Figure A1. Professional Output Circuit
TXP
TXN
load using no cable. The circuit
110
and a output drive level of
load to the part which is too
resistor in parallel with the
1
source
XLR
load
re-
used for optical connectors for digital audio since
they are usually TTL compatible. This circuit is
also useful when driving multiple digital audio out-
puts since RS422 line drivers have TTL interfaces.
The transformer should be capable of operating
from 1.5 to 14 MHz, which is the audio data rate of
25 kHz to 108 kHz after biphase-mark encoding.
Transformers provide isolation from ground loops,
60Hz noise, and common mode noise and interfer-
ence. One of the important considerations when
choosing transformers is minimizing shunt capaci-
tance between primary and secondary windings.
The higher the shunt capacitance, the lower the iso-
lation between primary and secondary, and the
more coupling of high frequency energy. This en-
ergy appears in the form of common mode noise on
the receive side ground and has the potential to de-
grade analog performance. Therefore, for best per-
formance, shielded transformers optimized for
minimum shunt capacitance should be used. The
following are a few typical transformers:
Pulse Engineering
Telecom Products Group
7250 Convoy Ct.
San Diego, CA 92111
CS8403A/4A
CS8403A/4A
Figure A3. TTL/CMOS Output Circuit
Figure A2. Consumer Output Circuit
TXN
TXP
TXN
TXP
374
90.9
CS8403A CS8404A
TTL or
CMOS Gate
DS239PP1
RCA
Phono