CS8427-CSZ datasheet(49/59 Pages) CIRRUS

49 / 59 page

CS8427

DS477F3

17. 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.

17.1

AES3 Transmitter External

Components

The output drivers on the CS8427 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 V peak-to-peak into a 110

Ω load with

no cable attached. Using the circuit in Figure 20,

the output of the transformer is short-circuit pro-

tected, has the proper source impedance, and pro-

vides 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 connector 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 21 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 22. 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.

17.2

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

CS8427

Figure 20. Professional Output Circuit

Figure 21. Consumer Output Circuit

374-R

TXP

90.9

Ω

TXP

TXN

RCA

Phono

CS8427

Figure 22. TTL/CMOS Output Circuit

TXP

TXN

TTL or

CMOS Gate

CS8427

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