Cirrus Logic CS8406 - Manual (Page 35)

DS580F6 35
CS8406
15.APPENDIX A: EXTERNAL AES3/SPDIF/IEC60958 TRANSMITTER
COMPONENTS
This section details the external components required to interface the AES3 transmitter to cables and fiber-optic
components.
15.1 AES3 Transmitter External Components
The output drivers on the CS8406 are designed to drive both the professional and consumer interfaces. The
AES3 and IEC60958-4 specifications call for a balanced output drive of 2-7 V peak-to-peak into a 110  ±
20% load with no cable attached. Using the circuit in Figure 14 , the output of the transformer is short-circuit
protected, has the p roper source impedance, and provides a 5 V 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 IEC60958-3 specification calls for an unbalanced drive circuit with an out-
put impedance of 75  ± 20% and a output drive level of 0.5 V peak-to-peak ± 20% when measured across
a 75  load using no cable. The circuit shown in Figure 15 only uses the TXP pin and provides the proper
output impedance and drive level using standard 1% resistors. If VL is set to +3.3 V, change 374 to 243 
and change 90.9  to 107 . The connector for a consumer application 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 16 . This circuit may be used for
optical connectors for digital audio since they usually have TTL or CMOS compatible inputs. This circuit is
also useful when driving multiple digital audio outputs since RS422 line drivers have TTL compatible inputs.
15.2 Isolating Transformer Requirements
Please refer to the application note AN134: AES and SPDIF Recommended Transformers for resources on
transformer selection.
374-R
TXP
90.9 
TXP
TXN
RCA
Phono
CS8406
110-(R
TXP
+R
TXN
)
TXP
TXN
XLR
Pin 1
CS8406
Figure 14. Professional Output Circuit Figure 15. Consumer Output Circuit (VL = 5.0 V)
TXP
TXN
TTL or
CMOS Gate
CS8406
Figure 16. TTL/CMOS Output Circuit