CS8405A-CS datasheet(34/37 Pages) CIRRUS

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CS8405A

DS469F2

14. APPENDIX A: EXTERNAL

AES3/SPDIF/IEC60958 TRANSMITTER

AND RECEIVER COMPONENTS

This section details the external components re-

quired to interface the AES3 transmitter and re-

ceiver 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 inter-

faces. The AES3 specification for profession-

al/broadcast

use

calls

for

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 V peak-to-peak into a

110

Ω load with no cable attached. Using the cir-

cuit in Figure 11, the output of the transformer is

short-circuit protected, has the proper source im-

pedance, and provides a 5 V 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 con-

nector grounded.

In the case of consumer use, the IEC60958 speci-

fications call for an unbalanced drive circuit with an

output impedance of 75

Ω and a output drive level

of 0.5 V 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

Ω and 107 Ω.

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 13. 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 dig-

ital 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.

110-(R

TXP+RTXN)

TXP

TXN

XLR

CS8405A

Figure 11. Professional Output Circuit

Figure 12. Consumer Output Circuit

374 - R

TX P

90. 9

Ω

TX P

TX N

C S 8405A

Figure 13. TTL/CMOS Output Circuit

TXP

TXN

TTL or

CMOS Gate

CS8405A

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