CS8405A Cirrus Logic, CS8405A Datasheet - Page 33

• Manufacturer Part Number: CS8405A
• Description: 96 KHZ DIGITAL AUDIO INTERFACE TRANSMITTER
• Manufacturer: Cirrus Logic

14. APPENDIX A: EXTERNAL
This section details the external components re-
quired to interface the AES3 transmitter to cables
and fiber-optic components.
14.1 AES3 Transmitter External
The output drivers on the CS8405A are designed to
drive both the professional and consumer interfac-
es. The AES3 specification for professional/broad-
cast use calls for a 110 Ω source impedance and a
balanced drive capability. Since the transmitter
output impedance is very low, a 110 Ω resistor
should be placed in series with one of the transmit
pins. The specifications call for a balanced output
drive of 2-7 volts peak-to-peak into a 110 Ω load
with no cable attached. Using the circuit in
Figure 11, 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 Ω 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.
DS469PP4
AES3/SPDIF/IEC60958
TRANSMITTER COMPONENTS
Components
Figure 11. Professional Output Circuit
CS8405A
TXP
TXN
110 Ω
CS8405A
Figure 13. TTL/CMOS Output Circuit
TXN
TXP
1
XLR
In the case of consumer use, the IEC60958 specifi-
cations call for an unbalanced drive circuit with an
output impedance of 75 Ω and a output drive level
of 0.5 volts peak-to-peak ±20% when measured
across a 75 Ω load using no cable. The circuit
shown in Figure 12 only uses the TXP pin and pro-
vides the proper output impedance and drive level
using standard 1% resistors. If VL+ is driven from
+3.3 V, use resistor values of 243 Ohms and
107 Ohms. The connector for a consumer applica-
tion 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 13. This circuit may be
used for optical connectors for digital audio since
they usually have TTL or CMOS compatible in-
puts. This circuit is also useful when driving multi-
ple digital audio outputs since RS422 line drivers
have TTL compatible inputs.
14.2 Isolating Transformer Requirements
Please refer to the application note AN134: AES
and SPDIF Recommended Transformers for re-
sources on transformer selection.
Figure 12. Consumer Output Circuit
CS8405A
TTL or
CMOS Gate
TXN
TXP
374 Ω
90.9 Ω
CS8405A
RCA
Phono
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