CS8405A-CS datasheet(33/36 Pages) CIRRUS

33 / 36 page

CS8405A

DS469PP4

14. APPENDIX A: EXTERNAL

AES3/SPDIF/IEC60958

TRANSMITTER COMPONENTS

This section details the external components re-

quired to interface the AES3 transmitter to cables

and fiber-optic components.

14.1

AES3 Transmitter External

Components

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.

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.

374

Ω

90.9

Ω

TXP

TXN

RCA

Phono

CS8405A

110

Ω

TXP

TXN

XLR

CS8405A

Figure 11. Professional Output Circuit

Figure 12. Consumer Output Circuit

TXP

TXN

TTL or

CMOS Gate

CS8405A

Figure 13. TTL/CMOS Output Circuit

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