CS8401A-IP ETC [List of Unclassifed Manufacturers], CS8401A-IP Datasheet - Page 28

• Manufacturer Part Number: CS8401A-IP
• Description: Digital Audio Interface Transmitter
• Manufacturer: ETC [List of Unclassifed Manufacturers]

Appendix A: RS422 Driver Information
The RS422 drivers on the CS8401A and CS8402A
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
should be placed in series with one of the transmit
pins. (A 110
former would, with the receiver impedance of 110 ,
provide a 55
The specifications call for a balanced output drive of
2-7 volts peak-to-peak into a 110 load with no ca-
ble 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
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 out-
put impedance of 75
of 0.5 volts peak-to-peak 20% when measured
across a 75
28
CS8401/2A
CS8401/2A
Figure A1. Professional Output Circuit
TXP
TXN
Figure A2. Consumer Output Circuit
TXP
TXN
load to the part which is too low.)
load using no cable. The circuit
resistor in parallel with the trans-
374
90.9
110
and a output drive level
load. Lastly,
1
RCA
Phono
XLR
resistor
source
shown in Figure A2 only uses the TXP pin and
provides the proper output impedance and drive
level using standard 1% resistors. The connector
for consumer 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 used for optical connectors for digital
audio since they are usually TTL compatible.
This circuit is also useful when driving multiple
digital audio outputs since RS422 line drivers
have TTL interfaces.
The transformer should be capable of operating
from 1.5 to 7 MHz, which is the audio data rate
of 25 kHz to 55 kHz after biphase-mark encod-
ing. Transformers provide isolation from ground
loops, 60 Hz noise, and common mode noise
and interference. One of the important considera-
tions when choosing transformers is minimizing
shunt capacitance between primary and secon-
dary windings. The higher the shunt capacitance,
the lower the isolation between primary and sec-
ondary, and the more coupling of high frequency
energy. This energy appears in the form of com-
mon mode noise on the receive side ground and
has the potential to degrade analog performance.
Therefore, for best performance, shielded trans-
formers optimized for min imum shunt
capacitance should be used. The following are a
few typical transformers:
Pulse Engineering
Telecom Products Group
7250 Convoy Ct.
San Diego, CA 92111
CS8401/2A
Figure A3. TTL/CMOS Output Circuit
TXP
TXN
CS8401A CS8402A
CMOS Gate
TTL or
DS60F1