CS4265_07 Datasheet, PDF (51/56 Pages) Cirrus Logic – 104 dB, 24-Bit, 192 kHz Stereo Audio CODEC

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 Ω ± 20%
and an 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 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 Ω in place of the 374 Ω resistor and a 107 Ω
resistor in place of the 90.9 Ω 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.
TXOUT
CS4265
374-R_TXP
90.9 Ω
RCA
Phono
Figure 42. Consumer Output Circuit (VD = 5 V)
TXOUT
CS4265
TTL or
CMOS Gate
Figure 43. TTL/CMOS Output Circuit
10.2 Isolating Transformer Requirements
Please refer to Cirrus application note AN134: AES and SPDIF Recommended Transformers for resources
on transformer selection.
DS657F2
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