Cirrus Logic CS4265 - Manual (Page 52)

52 DS657F3
CS4265
10.EXTERNAL IEC60958-3 TRANSMITTER COMPONENTS
This section details the external components required to interface the IEC60958-3 transmitter to cables and fiber-
optic components.
10.1 IEC60958-3 Transmitter External Components
The IEC60958-3 specifications call for an unbalanced drive circuit with an output impedance of 75  
and an output drive level of 0.5 volts peak-to-peak ±20% when measured across a 75  load using no cable.
The circuit shown in Figure 42 provides the proper output impedance and drive level using standard 1% re-
sistors. If VD is driven from +3.3 V, use resistor values of 243  in place of the 374  resistor and a 107 
resistor in place of the 90.9  resistor. The standard connector for a consumer application is an RCA phono
socket.
The TXOUT pin may be used to drive TTL or CMOS gates as shown in Figure 43 . This circuit may be used
for optical connectors for digital audio as they typically implement TTL or CMOS compatible inputs. This cir-
cuit is also useful when driving multiple digital audio outputs as RS422 line drivers typically implement TTL
compatible inputs.
10.2 Isolating Transformer Requirements
Please refer to Cirrus application note AN134: AES and SPDIF Recommended Transformers for resources
on transformer selection.
374-R
TXP
90.9 
TXOUT
RCA
Phono
Figure 42. Consumer Output Circuit (VD = 5 V)
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TXOUT
TTL or
CMOS Gate
Figure 43. TTL/CMOS Output Circuit
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